diff --git a/core/src/main/java/org/bouncycastle/asn1/ASN1BitString.java b/core/src/main/java/org/bouncycastle/asn1/ASN1BitString.java
index b5ada96794..3f1d4f5a31 100644
--- a/core/src/main/java/org/bouncycastle/asn1/ASN1BitString.java
+++ b/core/src/main/java/org/bouncycastle/asn1/ASN1BitString.java
@@ -247,7 +247,7 @@ public String getString()
             throw new ASN1ParsingException("Internal error encoding BitString: " + e.getMessage(), e);
         }
 
-        StringBuffer buf = new StringBuffer(1 + string.length * 2);
+        StringBuilder buf = new StringBuilder(1 + string.length * 2);
         buf.append('#');
 
         for (int i = 0; i != string.length; i++)
diff --git a/core/src/main/java/org/bouncycastle/asn1/ASN1Sequence.java b/core/src/main/java/org/bouncycastle/asn1/ASN1Sequence.java
index 66c22ec9f3..39a8992be9 100644
--- a/core/src/main/java/org/bouncycastle/asn1/ASN1Sequence.java
+++ b/core/src/main/java/org/bouncycastle/asn1/ASN1Sequence.java
@@ -383,7 +383,7 @@ public String toString()
             return "[]";
         }
 
-        StringBuffer sb = new StringBuffer();
+        StringBuilder sb = new StringBuilder();
         sb.append('[');
         for (int i = 0;;)
         {
diff --git a/core/src/main/java/org/bouncycastle/asn1/ASN1Set.java b/core/src/main/java/org/bouncycastle/asn1/ASN1Set.java
index 8cd3ad583b..516f98a2a5 100644
--- a/core/src/main/java/org/bouncycastle/asn1/ASN1Set.java
+++ b/core/src/main/java/org/bouncycastle/asn1/ASN1Set.java
@@ -423,7 +423,7 @@ public String toString()
             return "[]";
         }
 
-        StringBuffer sb = new StringBuffer();
+        StringBuilder sb = new StringBuilder();
         sb.append('[');
         for (int i = 0;;)
         {
diff --git a/core/src/main/java/org/bouncycastle/asn1/x500/style/IETFUtils.java b/core/src/main/java/org/bouncycastle/asn1/x500/style/IETFUtils.java
index 958de0c2ad..03726cd51b 100644
--- a/core/src/main/java/org/bouncycastle/asn1/x500/style/IETFUtils.java
+++ b/core/src/main/java/org/bouncycastle/asn1/x500/style/IETFUtils.java
@@ -33,7 +33,7 @@ private static String unescape(String elt)
 
         boolean escaped = false;
         boolean quoted = false;
-        StringBuffer buf = new StringBuffer(elt.length());
+        StringBuilder buf = new StringBuilder(elt.length());
         int start = 0;
 
         // if it's an escaped hash string and not an actual encoding in string form
@@ -367,7 +367,7 @@ public static void appendTypeAndValue(
 
     public static String valueToString(ASN1Encodable value)
     {
-        StringBuffer vBuf = new StringBuffer();
+        StringBuilder vBuf = new StringBuilder();
 
         if (value instanceof ASN1String && !(value instanceof ASN1UniversalString))
         {
@@ -507,12 +507,12 @@ private static ASN1Primitive decodeObject(String oValue)
     public static String stripInternalSpaces(
         String str)
     {
-        if (str.indexOf("  ") < 0)
+        if (!str.contains("  "))
         {
             return str;
         }
 
-        StringBuffer res = new StringBuffer();
+        StringBuilder res = new StringBuilder();
 
         char c1 = str.charAt(0);
         res.append(c1);
diff --git a/core/src/main/java/org/bouncycastle/asn1/x509/CRLDistPoint.java b/core/src/main/java/org/bouncycastle/asn1/x509/CRLDistPoint.java
index 1aa3f38d04..4c1425a18c 100644
--- a/core/src/main/java/org/bouncycastle/asn1/x509/CRLDistPoint.java
+++ b/core/src/main/java/org/bouncycastle/asn1/x509/CRLDistPoint.java
@@ -81,7 +81,7 @@ public ASN1Primitive toASN1Primitive()
 
     public String toString()
     {
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         String       sep = Strings.lineSeparator();
 
         buf.append("CRLDistPoint:");
diff --git a/core/src/main/java/org/bouncycastle/asn1/x509/CertificatePolicies.java b/core/src/main/java/org/bouncycastle/asn1/x509/CertificatePolicies.java
index 5b4385a24f..54301ff1b9 100644
--- a/core/src/main/java/org/bouncycastle/asn1/x509/CertificatePolicies.java
+++ b/core/src/main/java/org/bouncycastle/asn1/x509/CertificatePolicies.java
@@ -112,14 +112,12 @@ public ASN1Primitive toASN1Primitive()
 
     public String toString()
     {
-        StringBuffer p = new StringBuffer();
-        for (int i = 0; i < policyInformation.length; i++)
-        {
-            if (p.length() != 0)
-            {
+        StringBuilder p = new StringBuilder();
+        for (PolicyInformation information : policyInformation) {
+            if (p.length() != 0) {
                 p.append(", ");
             }
-            p.append(policyInformation[i]);
+            p.append(information);
         }
 
         return "CertificatePolicies: [" + p + "]";
diff --git a/core/src/main/java/org/bouncycastle/asn1/x509/GeneralName.java b/core/src/main/java/org/bouncycastle/asn1/x509/GeneralName.java
index 20c19100e4..521745562e 100644
--- a/core/src/main/java/org/bouncycastle/asn1/x509/GeneralName.java
+++ b/core/src/main/java/org/bouncycastle/asn1/x509/GeneralName.java
@@ -248,7 +248,7 @@ public ASN1Encodable getName()
 
     public String toString()
     {
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
 
         buf.append(tag);
         buf.append(": ");
diff --git a/core/src/main/java/org/bouncycastle/asn1/x509/GeneralNames.java b/core/src/main/java/org/bouncycastle/asn1/x509/GeneralNames.java
index 5ba472bf84..6308f5f6b2 100644
--- a/core/src/main/java/org/bouncycastle/asn1/x509/GeneralNames.java
+++ b/core/src/main/java/org/bouncycastle/asn1/x509/GeneralNames.java
@@ -95,7 +95,7 @@ public ASN1Primitive toASN1Primitive()
 
     public String toString()
     {
-        StringBuffer  buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         String        sep = Strings.lineSeparator();
 
         buf.append("GeneralNames:");
diff --git a/core/src/main/java/org/bouncycastle/asn1/x509/PKIXNameConstraintValidator.java b/core/src/main/java/org/bouncycastle/asn1/x509/PKIXNameConstraintValidator.java
index b918f9800e..a0f6f6e321 100644
--- a/core/src/main/java/org/bouncycastle/asn1/x509/PKIXNameConstraintValidator.java
+++ b/core/src/main/java/org/bouncycastle/asn1/x509/PKIXNameConstraintValidator.java
@@ -1825,7 +1825,7 @@ private static String extractHostFromURL(String url)
         // remove ':' after protocol, e.g. https:
         String sub = url.substring(url.indexOf(':') + 1);
         // extract host from Common Internet Scheme Syntax, e.g. https://
-        if (sub.indexOf("//") != -1)
+        if (sub.contains("//"))
         {
             sub = sub.substring(sub.indexOf("//") + 2);
         }
diff --git a/core/src/main/java/org/bouncycastle/crypto/engines/CramerShoupCiphertext.java b/core/src/main/java/org/bouncycastle/crypto/engines/CramerShoupCiphertext.java
index edf1bd23ac..6aa017a016 100644
--- a/core/src/main/java/org/bouncycastle/crypto/engines/CramerShoupCiphertext.java
+++ b/core/src/main/java/org/bouncycastle/crypto/engines/CramerShoupCiphertext.java
@@ -96,7 +96,7 @@ public void setV(BigInteger v)
 
     public String toString()
     {
-        StringBuffer result = new StringBuffer();
+        StringBuilder result = new StringBuilder();
 
         result.append("u1: " + u1.toString());
         result.append("\nu2: " + u2.toString());
diff --git a/core/src/main/java/org/bouncycastle/i18n/filter/HTMLFilter.java b/core/src/main/java/org/bouncycastle/i18n/filter/HTMLFilter.java
index b9904bc708..5791223f70 100644
--- a/core/src/main/java/org/bouncycastle/i18n/filter/HTMLFilter.java
+++ b/core/src/main/java/org/bouncycastle/i18n/filter/HTMLFilter.java
@@ -9,7 +9,7 @@ public class HTMLFilter implements Filter
 
     public String doFilter(String input) 
     {
-        StringBuffer buf = new StringBuffer(input);
+        StringBuilder buf = new StringBuilder(input);
         int i = 0;
         while (i < buf.length()) 
         {
diff --git a/core/src/main/java/org/bouncycastle/math/ec/ECPoint.java b/core/src/main/java/org/bouncycastle/math/ec/ECPoint.java
index 44349f5a4e..24ca684cf1 100644
--- a/core/src/main/java/org/bouncycastle/math/ec/ECPoint.java
+++ b/core/src/main/java/org/bouncycastle/math/ec/ECPoint.java
@@ -460,7 +460,7 @@ public String toString()
             return "INF";
         }
 
-        StringBuffer sb = new StringBuffer();
+        StringBuilder sb = new StringBuilder();
         sb.append('(');
         sb.append(getRawXCoord());
         sb.append(',');
diff --git a/core/src/main/java/org/bouncycastle/math/ec/tools/DiscoverEndomorphisms.java b/core/src/main/java/org/bouncycastle/math/ec/tools/DiscoverEndomorphisms.java
index f77a1a37b1..4b27fc8018 100644
--- a/core/src/main/java/org/bouncycastle/math/ec/tools/DiscoverEndomorphisms.java
+++ b/core/src/main/java/org/bouncycastle/math/ec/tools/DiscoverEndomorphisms.java
@@ -201,7 +201,7 @@ private static void printGLVTypeBParameters(X9ECParameters x9, BigInteger lambda
 
     private static void printProperty(String name, Object value)
     {
-        StringBuffer sb = new StringBuffer("  ");
+        StringBuilder sb = new StringBuilder("  ");
         sb.append(name);
         while (sb.length() < 20)
         {
diff --git a/core/src/main/java/org/bouncycastle/pqc/legacy/math/linearalgebra/GF2Matrix.java b/core/src/main/java/org/bouncycastle/pqc/legacy/math/linearalgebra/GF2Matrix.java
index 7b17571acd..24c31a0585 100644
--- a/core/src/main/java/org/bouncycastle/pqc/legacy/math/linearalgebra/GF2Matrix.java
+++ b/core/src/main/java/org/bouncycastle/pqc/legacy/math/linearalgebra/GF2Matrix.java
@@ -1253,7 +1253,7 @@ public String toString()
             d = length - 1;
         }
 
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         for (int i = 0; i < numRows; i++)
         {
             buf.append(i + ": ");
diff --git a/core/src/main/java/org/bouncycastle/pqc/legacy/math/linearalgebra/GF2Vector.java b/core/src/main/java/org/bouncycastle/pqc/legacy/math/linearalgebra/GF2Vector.java
index b0fa762acd..0fe699f469 100644
--- a/core/src/main/java/org/bouncycastle/pqc/legacy/math/linearalgebra/GF2Vector.java
+++ b/core/src/main/java/org/bouncycastle/pqc/legacy/math/linearalgebra/GF2Vector.java
@@ -516,7 +516,7 @@ public int hashCode()
      */
     public String toString()
     {
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         for (int i = 0; i < length; i++)
         {
             if ((i != 0) && ((i & 0x1f) == 0))
diff --git a/core/src/main/java/org/bouncycastle/pqc/legacy/math/linearalgebra/GF2mVector.java b/core/src/main/java/org/bouncycastle/pqc/legacy/math/linearalgebra/GF2mVector.java
index 73f4192b4a..173d62b330 100644
--- a/core/src/main/java/org/bouncycastle/pqc/legacy/math/linearalgebra/GF2mVector.java
+++ b/core/src/main/java/org/bouncycastle/pqc/legacy/math/linearalgebra/GF2mVector.java
@@ -233,7 +233,7 @@ public int hashCode()
      */
     public String toString()
     {
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         for (int i = 0; i < vector.length; i++)
         {
             for (int j = 0; j < field.getDegree(); j++)
diff --git a/core/src/main/java/org/bouncycastle/pqc/legacy/math/ntru/polynomial/BigDecimalPolynomial.java b/core/src/main/java/org/bouncycastle/pqc/legacy/math/ntru/polynomial/BigDecimalPolynomial.java
index f9eb5c8149..87cd1febe9 100644
--- a/core/src/main/java/org/bouncycastle/pqc/legacy/math/ntru/polynomial/BigDecimalPolynomial.java
+++ b/core/src/main/java/org/bouncycastle/pqc/legacy/math/ntru/polynomial/BigDecimalPolynomial.java
@@ -1,6 +1,7 @@
 package org.bouncycastle.pqc.legacy.math.ntru.polynomial;
 
 import java.math.BigDecimal;
+import java.math.RoundingMode;
 
 /**
  * A polynomial with {@link BigDecimal} coefficients.
@@ -214,7 +215,7 @@ public BigIntPolynomial round()
         BigIntPolynomial p = new BigIntPolynomial(N);
         for (int i = 0; i < N; i++)
         {
-            p.coeffs[i] = coeffs[i].setScale(0, BigDecimal.ROUND_HALF_EVEN).toBigInteger();
+            p.coeffs[i] = coeffs[i].setScale(0, RoundingMode.HALF_EVEN).toBigInteger();
         }
         return p;
     }
diff --git a/core/src/main/java/org/bouncycastle/pqc/legacy/math/ntru/polynomial/BigIntPolynomial.java b/core/src/main/java/org/bouncycastle/pqc/legacy/math/ntru/polynomial/BigIntPolynomial.java
index 50f1517782..d635bb46c7 100644
--- a/core/src/main/java/org/bouncycastle/pqc/legacy/math/ntru/polynomial/BigIntPolynomial.java
+++ b/core/src/main/java/org/bouncycastle/pqc/legacy/math/ntru/polynomial/BigIntPolynomial.java
@@ -2,6 +2,7 @@
 
 import java.math.BigDecimal;
 import java.math.BigInteger;
+import java.math.RoundingMode;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -284,14 +285,14 @@ public BigDecimalPolynomial div(BigDecimal divisor, int decimalPlaces)
         BigInteger max = maxCoeffAbs();
         int coeffLength = (int)(max.bitLength() * LOG_10_2) + 1;
         // factor = 1/divisor
-        BigDecimal factor = Constants.BIGDEC_ONE.divide(divisor, coeffLength + decimalPlaces + 1, BigDecimal.ROUND_HALF_EVEN);
+        BigDecimal factor = Constants.BIGDEC_ONE.divide(divisor, coeffLength + decimalPlaces + 1, RoundingMode.HALF_EVEN);
 
         // multiply each coefficient by factor
         BigDecimalPolynomial p = new BigDecimalPolynomial(coeffs.length);
         for (int i = 0; i < coeffs.length; i++)
         // multiply, then truncate after decimalPlaces so subsequent operations aren't slowed down
         {
-            p.coeffs[i] = new BigDecimal(coeffs[i]).multiply(factor).setScale(decimalPlaces, BigDecimal.ROUND_HALF_EVEN);
+            p.coeffs[i] = new BigDecimal(coeffs[i]).multiply(factor).setScale(decimalPlaces, RoundingMode.HALF_EVEN);
         }
 
         return p;
diff --git a/core/src/main/java/org/bouncycastle/util/Fingerprint.java b/core/src/main/java/org/bouncycastle/util/Fingerprint.java
index 7027d4948c..63f138286f 100644
--- a/core/src/main/java/org/bouncycastle/util/Fingerprint.java
+++ b/core/src/main/java/org/bouncycastle/util/Fingerprint.java
@@ -64,7 +64,7 @@ public byte[] getFingerprint()
 
     public String toString()
     {
-        StringBuffer sb = new StringBuffer();
+        StringBuilder sb = new StringBuilder();
         for (int i = 0; i != fingerprint.length; i++)
         {
             if (i > 0)
diff --git a/core/src/main/java/org/bouncycastle/util/test/SimpleTest.java b/core/src/main/java/org/bouncycastle/util/test/SimpleTest.java
index 2d29635e54..2b6ddf0dde 100644
--- a/core/src/main/java/org/bouncycastle/util/test/SimpleTest.java
+++ b/core/src/main/java/org/bouncycastle/util/test/SimpleTest.java
@@ -284,9 +284,9 @@ public Exception testException(String failMessage, String exceptionClass, TestEx
         {
             if (failMessage != null)
             {
-                isTrue(e.getMessage(), e.getMessage().indexOf(failMessage) >= 0);
+                isTrue(e.getMessage(), e.getMessage().contains(failMessage));
             }
-            isTrue(e.getMessage(),e.getClass().getName().indexOf(exceptionClass) >= 0);
+            isTrue(e.getMessage(), e.getClass().getName().contains(exceptionClass));
             return e;
         }
         return null;
diff --git a/core/src/test/java/org/bouncycastle/crypto/test/BlockCipherResetTest.java b/core/src/test/java/org/bouncycastle/crypto/test/BlockCipherResetTest.java
index f267ef5eaa..5599c5e0f6 100644
--- a/core/src/test/java/org/bouncycastle/crypto/test/BlockCipherResetTest.java
+++ b/core/src/test/java/org/bouncycastle/crypto/test/BlockCipherResetTest.java
@@ -115,7 +115,7 @@ private void testReset(String test,
         cipher1.init(true, params);
 
         byte[] plaintext = new byte[cipher1.getBlockSize()];
-        byte[] ciphertext = new byte[(cipher1.getAlgorithmName().indexOf("PGPCFBwithIV")) > -1 ? 2 * cipher1.getBlockSize() + 2
+        byte[] ciphertext = new byte[cipher1.getAlgorithmName().contains("PGPCFBwithIV") ? 2 * cipher1.getBlockSize() + 2
             : cipher1.getBlockSize()];
 
         // Establish baseline answer
@@ -191,7 +191,7 @@ private static void crypt(BlockCipher cipher1, boolean encrypt, byte[] plaintext
         throws InvalidCipherTextException
     {
         cipher1.processBlock(plaintext, 0, output, 0);
-        if ((cipher1.getAlgorithmName().indexOf("PGPCFBwithIV") > -1) && !encrypt)
+        if ((cipher1.getAlgorithmName().contains("PGPCFBwithIV")) && !encrypt)
         {
             // Process past IV in first block
             cipher1.processBlock(plaintext, cipher1.getBlockSize(), output, 0);
diff --git a/core/src/test/java/org/bouncycastle/crypto/test/HCFamilyVecTest.java b/core/src/test/java/org/bouncycastle/crypto/test/HCFamilyVecTest.java
index 99f70e868b..e5134a1949 100644
--- a/core/src/test/java/org/bouncycastle/crypto/test/HCFamilyVecTest.java
+++ b/core/src/test/java/org/bouncycastle/crypto/test/HCFamilyVecTest.java
@@ -93,7 +93,7 @@ private void runAllVectors(StreamCipher hc, String fileName, PeekableLineReader
 
     private String dellChar(String s, char c)
     {
-        StringBuffer b = new StringBuffer();
+        StringBuilder b = new StringBuilder();
 
         for (int i = 0; i != s.length(); i++)
         {
diff --git a/core/src/test/java/org/bouncycastle/crypto/test/Haraka256DigestTest.java b/core/src/test/java/org/bouncycastle/crypto/test/Haraka256DigestTest.java
index 15dc36be56..1a7c31844a 100644
--- a/core/src/test/java/org/bouncycastle/crypto/test/Haraka256DigestTest.java
+++ b/core/src/test/java/org/bouncycastle/crypto/test/Haraka256DigestTest.java
@@ -43,7 +43,7 @@ public void testInputTooShort()
         }
         catch (IllegalStateException ilarex)
         {
-            isTrue("message", contains(ilarex.getMessage(), "input must be exactly 32 bytes"));
+            isTrue("message", ilarex.getMessage().contains("input must be exactly 32 bytes"));
         }
     }
 
@@ -59,7 +59,7 @@ public void testInputTooLong()
         }
         catch (IllegalArgumentException ilarex)
         {
-            isTrue("long message", contains(ilarex.getMessage(), "total input cannot be more than 32 bytes"));
+            isTrue("long message", ilarex.getMessage().contains("total input cannot be more than 32 bytes"));
         }
     }
 
@@ -80,7 +80,7 @@ public void testOutput()
         }
         catch (IllegalArgumentException ilarex)
         {
-            isTrue("message 1", contains(ilarex.getMessage(), "output too short to receive digest"));
+            isTrue("message 1", ilarex.getMessage().contains("output too short to receive digest"));
         }
 
         //
@@ -97,7 +97,7 @@ public void testOutput()
         }
         catch (IllegalArgumentException ilarex)
         {
-            isTrue("message 2", contains(ilarex.getMessage(), "output too short to receive digest"));
+            isTrue("message 2", ilarex.getMessage().contains("output too short to receive digest"));
         }
 
 
@@ -163,11 +163,6 @@ void testMonty()
         }
     }
 
-    private boolean contains(String message, String sub)
-    {
-        return message.indexOf(sub) >= 0;
-    }
-
     public void performTest()
         throws Exception
     {
diff --git a/core/src/test/java/org/bouncycastle/crypto/test/Haraka512DigestTest.java b/core/src/test/java/org/bouncycastle/crypto/test/Haraka512DigestTest.java
index 0cb4053545..3966058801 100644
--- a/core/src/test/java/org/bouncycastle/crypto/test/Haraka512DigestTest.java
+++ b/core/src/test/java/org/bouncycastle/crypto/test/Haraka512DigestTest.java
@@ -42,7 +42,7 @@ public void testInputTooShort()
         }
         catch (IllegalStateException ilarex)
         {
-            isTrue("message", contains(ilarex.getMessage(), "input must be exactly 64 bytes"));
+            isTrue("message", ilarex.getMessage().contains("input must be exactly 64 bytes"));
         }
     }
 
@@ -58,7 +58,7 @@ public void testInputTooLong()
         }
         catch (IllegalArgumentException ilarex)
         {
-            isTrue("message", contains(ilarex.getMessage(), "total input cannot be more than 64 bytes"));
+            isTrue("message", ilarex.getMessage().contains("total input cannot be more than 64 bytes"));
         }
     }
 
@@ -78,7 +78,7 @@ public void testOutput()
         }
         catch (IllegalArgumentException ilarex)
         {
-            isTrue("message", contains(ilarex.getMessage(), "output too short to receive digest"));
+            isTrue("message", ilarex.getMessage().contains("output too short to receive digest"));
         }
 
         //
@@ -95,7 +95,7 @@ public void testOutput()
         }
         catch (IllegalArgumentException ilarex)
         {
-            isTrue("message", contains(ilarex.getMessage(), "output too short to receive digest"));
+            isTrue("message", ilarex.getMessage().contains("output too short to receive digest"));
         }
 
         //
@@ -169,11 +169,6 @@ void testMonty()
         }
     }
 
-    private boolean contains(String message, String sub)
-    {
-        return message.indexOf(sub) >= 0;
-    }
-
     public void performTest()
         throws Exception
     {
diff --git a/core/src/test/java/org/bouncycastle/crypto/test/LEATest.java b/core/src/test/java/org/bouncycastle/crypto/test/LEATest.java
index e60e9e8720..286ee3e00e 100644
--- a/core/src/test/java/org/bouncycastle/crypto/test/LEATest.java
+++ b/core/src/test/java/org/bouncycastle/crypto/test/LEATest.java
@@ -186,7 +186,7 @@ else if (line.startsWith("IV:"))
             }
             else if (line.startsWith("Test:"))
             {
-                if (comment.indexOf("ECB") >= 0)
+                if (comment.contains("ECB"))
                 {
                     LEAEngine engine = new LEAEngine();
                     if (line.endsWith("Encrypt"))
@@ -216,11 +216,11 @@ else if (line.endsWith("Decrypt"))
                     }
 
                 }
-                else if (comment.indexOf("CTR") >= 0 || comment.indexOf("CBC") >= 0)
+                else if (comment.contains("CTR") || comment.contains("CBC"))
                 {
                     BlockCipher engine;
 
-                    if (comment.indexOf("CBC") >= 0)
+                    if (comment.contains("CBC"))
                     {
                         engine = CBCBlockCipher.newInstance(new LEAEngine());
                     }
diff --git a/core/src/test/java/org/bouncycastle/math/ec/test/ECPointPerformanceTest.java b/core/src/test/java/org/bouncycastle/math/ec/test/ECPointPerformanceTest.java
index 9be8d3ea7b..2d9eaa4ded 100644
--- a/core/src/test/java/org/bouncycastle/math/ec/test/ECPointPerformanceTest.java
+++ b/core/src/test/java/org/bouncycastle/math/ec/test/ECPointPerformanceTest.java
@@ -76,7 +76,7 @@ private void randMult(String label, X9ECParameters spec) throws Exception
 
                 double avgRate = randMult(random, g, n);
                 String coordName = COORD_NAMES[coord];
-                StringBuffer sb = new StringBuffer();
+                StringBuilder sb = new StringBuilder();
                 sb.append("   ");
                 sb.append(defaultCoord ? '*' : ' ');
                 sb.append(coordName);
diff --git a/core/src/test/java/org/bouncycastle/math/ec/test/F2mProofer.java b/core/src/test/java/org/bouncycastle/math/ec/test/F2mProofer.java
index b687520337..9dec0b2b51 100644
--- a/core/src/test/java/org/bouncycastle/math/ec/test/F2mProofer.java
+++ b/core/src/test/java/org/bouncycastle/math/ec/test/F2mProofer.java
@@ -40,7 +40,7 @@ private String pointToString(ECPoint.F2m p)
         int m = x.getM();
         int len = m / 2 + 5;
 
-        StringBuffer sb = new StringBuffer(len);
+        StringBuilder sb = new StringBuilder(len);
         sb.append('(');
         sb.append(x.toBigInteger().toString(16));
         sb.append(", ");
diff --git a/core/src/test/java/org/bouncycastle/pqc/crypto/lms/HSSTests.java b/core/src/test/java/org/bouncycastle/pqc/crypto/lms/HSSTests.java
index 2ececd90d2..20abf0cfa6 100644
--- a/core/src/test/java/org/bouncycastle/pqc/crypto/lms/HSSTests.java
+++ b/core/src/test/java/org/bouncycastle/pqc/crypto/lms/HSSTests.java
@@ -115,7 +115,7 @@ private List<byte[]> loadVector(String vector)
         BufferedReader bin = new BufferedReader(new InputStreamReader(inputStream));
         String line;
         List<byte[]> blocks = new ArrayList<byte[]>();
-        StringBuffer sw = new StringBuffer();
+        StringBuilder sw = new StringBuilder();
         while ((line = bin.readLine()) != null)
         {
             if (line.startsWith("!"))
diff --git a/core/src/test/java/org/bouncycastle/pqc/crypto/test/MLDSATest.java b/core/src/test/java/org/bouncycastle/pqc/crypto/test/MLDSATest.java
index d3e5a14588..102434e295 100644
--- a/core/src/test/java/org/bouncycastle/pqc/crypto/test/MLDSATest.java
+++ b/core/src/test/java/org/bouncycastle/pqc/crypto/test/MLDSATest.java
@@ -653,7 +653,7 @@ private static List<TestVector> parseTestVectors(InputStream src)
             }
 
             // Look for test vector array start
-            if (line.indexOf("dilithium_rejection_testvectors[] = ") >= 0)
+            if (line.contains("dilithium_rejection_testvectors[] = "))
             {
                 continue;
             }
@@ -685,7 +685,7 @@ private static List<TestVector> parseTestVectors(InputStream src)
                 }
 
                 // Check for field end
-                if (line.indexOf("},") >= 0)
+                if (line.contains("},"))
                 {
                     setField(currentVector, currentField, currentBytes);
                     currentField = null;
diff --git a/core/src/test/java/org/bouncycastle/pqc/crypto/test/SphincsPlusTest.java b/core/src/test/java/org/bouncycastle/pqc/crypto/test/SphincsPlusTest.java
index 5fea355d8f..eedb7d09ef 100644
--- a/core/src/test/java/org/bouncycastle/pqc/crypto/test/SphincsPlusTest.java
+++ b/core/src/test/java/org/bouncycastle/pqc/crypto/test/SphincsPlusTest.java
@@ -161,7 +161,7 @@ else if (simple)
                         SPHINCSPlusPrivateKeyParameters privParams = (SPHINCSPlusPrivateKeyParameters)kp.getPrivate();
 
                         // FIXME No OIDs for simple variants of SPHINCS+
-                        if (name.indexOf("-simple") < 0)
+                        if (!name.contains("-simple"))
                         {
                             pubParams = (SPHINCSPlusPublicKeyParameters)PublicKeyFactory.createKey(
                                 SubjectPublicKeyInfoFactory.createSubjectPublicKeyInfo(pubParams));
diff --git a/core/src/test/java/org/bouncycastle/util/encoders/test/AbstractCoderTest.java b/core/src/test/java/org/bouncycastle/util/encoders/test/AbstractCoderTest.java
index 0da54d9b78..04a5ccad2e 100644
--- a/core/src/test/java/org/bouncycastle/util/encoders/test/AbstractCoderTest.java
+++ b/core/src/test/java/org/bouncycastle/util/encoders/test/AbstractCoderTest.java
@@ -202,7 +202,7 @@ private void addSpace(ByteArrayOutputStream out)
 
     private String convertBytesToString(byte[] encoded)
     {
-        StringBuffer    b = new StringBuffer();
+        StringBuilder b = new StringBuilder();
         
         for (int i = 0; i != encoded.length; i++)
         {
diff --git a/mail/src/test/java/org/bouncycastle/mail/smime/test/CMSTestUtil.java b/mail/src/test/java/org/bouncycastle/mail/smime/test/CMSTestUtil.java
index 61950472a5..9a80db9afb 100644
--- a/mail/src/test/java/org/bouncycastle/mail/smime/test/CMSTestUtil.java
+++ b/mail/src/test/java/org/bouncycastle/mail/smime/test/CMSTestUtil.java
@@ -178,7 +178,7 @@ public class CMSTestUtil
     public static String dumpBase64(
         byte[]  data)
     {
-        StringBuffer    buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         
         data = Base64.encode(data);
         
diff --git a/pg/src/test/java/org/bouncycastle/openpgp/api/test/ChangeKeyPassphraseTest.java b/pg/src/test/java/org/bouncycastle/openpgp/api/test/ChangeKeyPassphraseTest.java
index ed24018f57..ac83880c6d 100644
--- a/pg/src/test/java/org/bouncycastle/openpgp/api/test/ChangeKeyPassphraseTest.java
+++ b/pg/src/test/java/org/bouncycastle/openpgp/api/test/ChangeKeyPassphraseTest.java
@@ -15,7 +15,7 @@ public class ChangeKeyPassphraseTest
     protected void performTestWith(OpenPGPApi api)
             throws PGPException, IOException
     {
-        if (System.getProperty("java.version").indexOf("1.5.") < 0)
+        if (!System.getProperty("java.version").contains("1.5."))
         {
             removeAEADPassphrase(api);
             addAEADPassphrase(api);
diff --git a/pg/src/test/java/org/bouncycastle/openpgp/test/ArmoredOutputStreamTest.java b/pg/src/test/java/org/bouncycastle/openpgp/test/ArmoredOutputStreamTest.java
index 1436460c7a..3c37db4dda 100644
--- a/pg/src/test/java/org/bouncycastle/openpgp/test/ArmoredOutputStreamTest.java
+++ b/pg/src/test/java/org/bouncycastle/openpgp/test/ArmoredOutputStreamTest.java
@@ -71,7 +71,7 @@ public void performTest()
         aOut.close();
 
         byte[] res = bOut.toByteArray();
-        StringBuffer sb = new StringBuffer();
+        StringBuilder sb = new StringBuilder();
         byte lastC = 0;
         for (int i = 0; i != res.length; i++)
         {
diff --git a/pg/src/test/java/org/bouncycastle/openpgp/test/PGPGeneralTest.java b/pg/src/test/java/org/bouncycastle/openpgp/test/PGPGeneralTest.java
index afd421d860..095f460a21 100644
--- a/pg/src/test/java/org/bouncycastle/openpgp/test/PGPGeneralTest.java
+++ b/pg/src/test/java/org/bouncycastle/openpgp/test/PGPGeneralTest.java
@@ -1119,7 +1119,7 @@ public void testPGPPublicKey()
 
     private boolean messageIs(String message, String s)
     {
-        return message.indexOf(s) >= 0;
+        return message.contains(s);
     }
 
     public void testAddRemoveCertification()
diff --git a/pkix/src/main/java/org/bouncycastle/mime/Headers.java b/pkix/src/main/java/org/bouncycastle/mime/Headers.java
index ed5a9d6e88..355feeda9e 100644
--- a/pkix/src/main/java/org/bouncycastle/mime/Headers.java
+++ b/pkix/src/main/java/org/bouncycastle/mime/Headers.java
@@ -75,7 +75,7 @@ public Headers(String contentType, String defaultContentTransferEncoding)
 
         contentTransferEncoding = this.getValues("Content-Transfer-Encoding") == null ? defaultContentTransferEncoding : this.getValues("Content-Transfer-Encoding")[0];
 
-        if (contentType.indexOf("multipart") >= 0)    // JVM compatibility
+        if (contentType.contains("multipart"))    // JVM compatibility
         {
             multipart = true;
             String bound = (String)contentTypeParameters.get("boundary");
@@ -145,7 +145,7 @@ public Headers(List<String> headerLines, String defaultContentTransferEncoding)
 
         contentTransferEncoding = this.getValues("Content-Transfer-Encoding") == null ? defaultContentTransferEncoding : this.getValues("Content-Transfer-Encoding")[0];
 
-        if (contentType.indexOf("multipart") >= 0)
+        if (contentType.contains("multipart"))
         {
             multipart = true;
             String bound = (String)contentTypeParameters.get("boundary");
diff --git a/pkix/src/main/java/org/bouncycastle/pkcs/jcajce/JcePKCSPBEOutputEncryptorBuilder.java b/pkix/src/main/java/org/bouncycastle/pkcs/jcajce/JcePKCSPBEOutputEncryptorBuilder.java
index dcdd08bf0b..0992eeecb0 100644
--- a/pkix/src/main/java/org/bouncycastle/pkcs/jcajce/JcePKCSPBEOutputEncryptorBuilder.java
+++ b/pkix/src/main/java/org/bouncycastle/pkcs/jcajce/JcePKCSPBEOutputEncryptorBuilder.java
@@ -307,7 +307,7 @@ private SecretKey simplifyPbeKey(SecretKey key)
         {
             String algName = algorithmNameFinder.getAlgorithmName(keyEncAlgorithm);
 
-            if (algName.indexOf("AES") >= 0)
+            if (algName.contains("AES"))
             {
                 key = new SecretKeySpec(key.getEncoded(), "AES");
             }
diff --git a/pkix/src/main/java/org/bouncycastle/pkix/ASN1PKIXNameConstraintValidator.java b/pkix/src/main/java/org/bouncycastle/pkix/ASN1PKIXNameConstraintValidator.java
index d77afc712a..d8e66d23a4 100644
--- a/pkix/src/main/java/org/bouncycastle/pkix/ASN1PKIXNameConstraintValidator.java
+++ b/pkix/src/main/java/org/bouncycastle/pkix/ASN1PKIXNameConstraintValidator.java
@@ -1813,7 +1813,7 @@ private static String extractHostFromURL(String url)
         // remove ':' after protocol, e.g. http:
         String sub = url.substring(url.indexOf(':') + 1);
         // extract host from Common Internet Scheme Syntax, e.g. https://
-        if (sub.indexOf("//") != -1)
+        if (sub.contains("//"))
         {
             sub = sub.substring(sub.indexOf("//") + 2);
         }
diff --git a/pkix/src/main/java/org/bouncycastle/pkix/util/filter/HTMLFilter.java b/pkix/src/main/java/org/bouncycastle/pkix/util/filter/HTMLFilter.java
index dd7bc962da..09cc4f01ee 100644
--- a/pkix/src/main/java/org/bouncycastle/pkix/util/filter/HTMLFilter.java
+++ b/pkix/src/main/java/org/bouncycastle/pkix/util/filter/HTMLFilter.java
@@ -9,7 +9,7 @@ public class HTMLFilter implements Filter
 
     public String doFilter(String input) 
     {
-        StringBuffer buf = new StringBuffer(input);
+        StringBuilder buf = new StringBuilder(input);
         int i = 0;
         while (i < buf.length()) 
         {
diff --git a/pkix/src/test/java/org/bouncycastle/cert/test/CertTest.java b/pkix/src/test/java/org/bouncycastle/cert/test/CertTest.java
index cf4ebacefc..9a57aa00ca 100644
--- a/pkix/src/test/java/org/bouncycastle/cert/test/CertTest.java
+++ b/pkix/src/test/java/org/bouncycastle/cert/test/CertTest.java
@@ -4662,7 +4662,7 @@ public void checkCreationComposite()
 
         cert.verify(lmsPub, "BCPQC");     // lms key only
 
-        if (System.getProperty("java.version").indexOf("1.5.") < 0)
+        if (!System.getProperty("java.version").contains("1.5."))
         {
             cert.verify(ecPub, new BouncyCastleProvider());      // ec key only
 
@@ -4768,7 +4768,7 @@ private void checkCompositeCertificateVerify()
 
         cert.verify(ecPub, BC);      // ec key only
 
-        if (System.getProperty("java.version").indexOf("1.5.") < 0)
+        if (!System.getProperty("java.version").contains("1.5."))
         {
             cert.verify(ecPub, new BouncyCastleProvider());      // ec key only
         }
diff --git a/pkix/src/test/java/org/bouncycastle/cms/test/AuthEnvelopedDataTest.java b/pkix/src/test/java/org/bouncycastle/cms/test/AuthEnvelopedDataTest.java
index 3472aa57f5..42fbbe0d84 100644
--- a/pkix/src/test/java/org/bouncycastle/cms/test/AuthEnvelopedDataTest.java
+++ b/pkix/src/test/java/org/bouncycastle/cms/test/AuthEnvelopedDataTest.java
@@ -445,7 +445,7 @@ public AttributeTable getAttributes(Map parameters)
 
         RecipientInformation recipient = (RecipientInformation)recipients.getRecipients().iterator().next();
 
-        if (System.getProperty("java.version").indexOf("1.5.") < 0)
+        if (!System.getProperty("java.version").contains("1.5."))
         {
             byte[] recData = recipient.getContent(new JceKeyTransAuthEnvelopedRecipient(_reciKP.getPrivate()).setProvider(BC));
             assertTrue(java.util.Arrays.equals(authData.getMac(), recipient.getMac()));
@@ -491,7 +491,7 @@ public AttributeTable getAttributes(Map parameters)
 
         RecipientInformation recipient = (RecipientInformation)recipients.getRecipients().iterator().next();
 
-        if (System.getProperty("java.version").indexOf("1.5.") < 0)
+        if (!System.getProperty("java.version").contains("1.5."))
         {
             byte[] recData = recipient.getContent(new JceKeyTransAuthEnvelopedRecipient(_reciKP.getPrivate()).setProvider(BC));
                                     
diff --git a/pkix/src/test/java/org/bouncycastle/cms/test/CMSTestUtil.java b/pkix/src/test/java/org/bouncycastle/cms/test/CMSTestUtil.java
index d143965ede..31e900b3d1 100644
--- a/pkix/src/test/java/org/bouncycastle/cms/test/CMSTestUtil.java
+++ b/pkix/src/test/java/org/bouncycastle/cms/test/CMSTestUtil.java
@@ -247,7 +247,7 @@ public static boolean isAeadAvailable()
     public static String dumpBase64(
         byte[]  data)
     {
-        StringBuffer    buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         
         data = Base64.encode(data);
         
diff --git a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/compositesignatures/CompositeIndex.java b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/compositesignatures/CompositeIndex.java
index 00f117cfa8..ea870e2469 100644
--- a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/compositesignatures/CompositeIndex.java
+++ b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/compositesignatures/CompositeIndex.java
@@ -136,11 +136,11 @@ static AlgorithmParameterSpec[] getKeyPairSpecs(ASN1ObjectIdentifier algorithm)
 
     static String getBaseName(String name)
     {
-        if (name.indexOf("RSA") >= 0)
+        if (name.contains("RSA"))
         {
             return "RSA";
         }
-        if (name.indexOf("ECDSA") >= 0)
+        if (name.contains("ECDSA"))
         {
             return "EC";
         }
diff --git a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/dh/DHUtil.java b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/dh/DHUtil.java
index f26b83bd06..b809458339 100644
--- a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/dh/DHUtil.java
+++ b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/dh/DHUtil.java
@@ -11,7 +11,7 @@ class DHUtil
 {
     static String privateKeyToString(String algorithm, BigInteger x, DHParameters dhParams)
     {
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         String       nl = Strings.lineSeparator();
 
         BigInteger y = dhParams.getG().modPow(x, dhParams.getP());
@@ -25,7 +25,7 @@ static String privateKeyToString(String algorithm, BigInteger x, DHParameters dh
 
     static String publicKeyToString(String algorithm, BigInteger y, DHParameters dhParams)
     {
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         String       nl = Strings.lineSeparator();
 
         buf.append(algorithm);
diff --git a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/dsa/BCDSAPrivateKey.java b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/dsa/BCDSAPrivateKey.java
index b0634bf036..e24ed64f89 100644
--- a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/dsa/BCDSAPrivateKey.java
+++ b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/dsa/BCDSAPrivateKey.java
@@ -178,7 +178,7 @@ private void writeObject(
 
     public String toString()
     {
-        StringBuffer    buf = new StringBuffer();
+        StringBuilder   buf = new StringBuilder();
         String          nl = Strings.lineSeparator();
 
         BigInteger y = getParams().getG().modPow(x, getParams().getP());
diff --git a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/dsa/BCDSAPublicKey.java b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/dsa/BCDSAPublicKey.java
index 0aa9691513..1c17ac875c 100644
--- a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/dsa/BCDSAPublicKey.java
+++ b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/dsa/BCDSAPublicKey.java
@@ -134,7 +134,7 @@ public BigInteger getY()
 
     public String toString()
     {
-        StringBuffer    buf = new StringBuffer();
+        StringBuilder   buf = new StringBuilder();
         String          nl = Strings.lineSeparator();
 
         buf.append("DSA Public Key [").append(DSAUtil.generateKeyFingerprint(y, getParams())).append("]").append(nl);
diff --git a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/gost/GOSTUtil.java b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/gost/GOSTUtil.java
index 772f25368e..fd0b7e753b 100644
--- a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/gost/GOSTUtil.java
+++ b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/gost/GOSTUtil.java
@@ -11,7 +11,7 @@ class GOSTUtil
 {
     static String privateKeyToString(String algorithm, BigInteger x, GOST3410Parameters gostParams)
     {
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         String        nl = Strings.lineSeparator();
 
         BigInteger y = gostParams.getA().modPow(x, gostParams.getP());
@@ -25,7 +25,7 @@ static String privateKeyToString(String algorithm, BigInteger x, GOST3410Paramet
 
     static String publicKeyToString(String algorithm, BigInteger y, GOST3410Parameters gostParams)
     {
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         String nl = Strings.lineSeparator();
 
         buf.append(algorithm);
diff --git a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/rsa/BCRSAPrivateCrtKey.java b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/rsa/BCRSAPrivateCrtKey.java
index 477c3f35ca..748677a3b2 100644
--- a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/rsa/BCRSAPrivateCrtKey.java
+++ b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/rsa/BCRSAPrivateCrtKey.java
@@ -278,7 +278,7 @@ private void writeObject(
 
     public String toString()
     {
-        StringBuffer    buf = new StringBuffer();
+        StringBuilder   buf = new StringBuilder();
         String          nl = Strings.lineSeparator();
 
         buf.append("RSA Private CRT Key [").append(
diff --git a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/rsa/BCRSAPrivateKey.java b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/rsa/BCRSAPrivateKey.java
index 215945d3eb..831ef85b69 100644
--- a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/rsa/BCRSAPrivateKey.java
+++ b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/rsa/BCRSAPrivateKey.java
@@ -189,7 +189,7 @@ private void writeObject(
 
     public String toString()
     {
-        StringBuffer    buf = new StringBuffer();
+        StringBuilder   buf = new StringBuilder();
         String          nl = Strings.lineSeparator();
 
         buf.append("RSA Private Key [").append(
diff --git a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/rsa/BCRSAPublicKey.java b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/rsa/BCRSAPublicKey.java
index 2d7e11b56c..09c5106314 100644
--- a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/rsa/BCRSAPublicKey.java
+++ b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/rsa/BCRSAPublicKey.java
@@ -154,7 +154,7 @@ public boolean equals(Object o)
 
     public String toString()
     {
-        StringBuffer    buf = new StringBuffer();
+        StringBuilder   buf = new StringBuilder();
         String          nl = Strings.lineSeparator();
 
         buf.append("RSA Public Key [").append(RSAUtil.generateKeyFingerprint(this.getModulus())).append("]")
diff --git a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/util/ECUtil.java b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/util/ECUtil.java
index 742fa14a50..b97fca2c68 100644
--- a/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/util/ECUtil.java
+++ b/prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/util/ECUtil.java
@@ -396,7 +396,7 @@ public static String getCurveName(
 
     public static String privateKeyToString(String algorithm, BigInteger d, org.bouncycastle.jce.spec.ECParameterSpec spec)
     {
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         String nl = Strings.lineSeparator();
 
         org.bouncycastle.math.ec.ECPoint q = new FixedPointCombMultiplier().multiply(spec.getG(), d).normalize();
@@ -411,7 +411,7 @@ public static String privateKeyToString(String algorithm, BigInteger d, org.boun
 
     public static String publicKeyToString(String algorithm, org.bouncycastle.math.ec.ECPoint q, org.bouncycastle.jce.spec.ECParameterSpec spec)
     {
-        StringBuffer buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         String nl = Strings.lineSeparator();
 
         buf.append(algorithm);
diff --git a/prov/src/main/java/org/bouncycastle/jcajce/provider/keystore/bcfks/BcFKSKeyStoreSpi.java b/prov/src/main/java/org/bouncycastle/jcajce/provider/keystore/bcfks/BcFKSKeyStoreSpi.java
index 3a30a5549b..e7e5e2b873 100644
--- a/prov/src/main/java/org/bouncycastle/jcajce/provider/keystore/bcfks/BcFKSKeyStoreSpi.java
+++ b/prov/src/main/java/org/bouncycastle/jcajce/provider/keystore/bcfks/BcFKSKeyStoreSpi.java
@@ -422,7 +422,7 @@ else if (key instanceof SecretKey)
                 String keyAlg = Strings.toUpperCase(key.getAlgorithm());
                 SecretKeyData secKeyData;
 
-                if (keyAlg.indexOf("AES") > -1)
+                if (keyAlg.contains("AES"))
                 {
                     secKeyData = new SecretKeyData(NISTObjectIdentifiers.aes, encodedKey);
                 }
diff --git a/prov/src/main/java/org/bouncycastle/jcajce/provider/keystore/pkcs12/PKCS12KeyStoreSpi.java b/prov/src/main/java/org/bouncycastle/jcajce/provider/keystore/pkcs12/PKCS12KeyStoreSpi.java
index 219efb6d8d..3613c55c56 100644
--- a/prov/src/main/java/org/bouncycastle/jcajce/provider/keystore/pkcs12/PKCS12KeyStoreSpi.java
+++ b/prov/src/main/java/org/bouncycastle/jcajce/provider/keystore/pkcs12/PKCS12KeyStoreSpi.java
@@ -1434,7 +1434,7 @@ private void syncFriendlyName()
         // TODO:delete comment
         //  Since we cannot add any function to the KeyStore Api we will run code when saving the store
         // to sync the friendlyNames with Alias depending on the storeParameter
-        /**
+        /*
          *     @Override
          *     public void setFriendlyName(String alias, String newFriendlyName, char[] password) throws UnrecoverableKeyException, NoSuchAlgorithmException
          *     {
diff --git a/prov/src/main/java/org/bouncycastle/jce/provider/JCEECPrivateKey.java b/prov/src/main/java/org/bouncycastle/jce/provider/JCEECPrivateKey.java
index 222d656e87..6ae013b1f8 100644
--- a/prov/src/main/java/org/bouncycastle/jce/provider/JCEECPrivateKey.java
+++ b/prov/src/main/java/org/bouncycastle/jce/provider/JCEECPrivateKey.java
@@ -416,7 +416,7 @@ public int hashCode()
 
     public String toString()
     {
-        StringBuffer    buf = new StringBuffer();
+        StringBuilder buf = new StringBuilder();
         String          nl = Strings.lineSeparator();
 
         buf.append("EC Private Key").append(nl);
diff --git a/prov/src/main/java/org/bouncycastle/jce/provider/JCEECPublicKey.java b/prov/src/main/java/org/bouncycastle/jce/provider/JCEECPublicKey.java
index d8276b2c5d..cdf75beb09 100644
--- a/prov/src/main/java/org/bouncycastle/jce/provider/JCEECPublicKey.java
+++ b/prov/src/main/java/org/bouncycastle/jce/provider/JCEECPublicKey.java
@@ -450,7 +450,7 @@ org.bouncycastle.jce.spec.ECParameterSpec engineGetSpec()
 
     public String toString()
     {
-        StringBuffer    buf = new StringBuffer();
+        StringBuilder   buf = new StringBuilder();
         String          nl = Strings.lineSeparator();
 
         buf.append("EC Public Key").append(nl);
diff --git a/prov/src/main/java/org/bouncycastle/jce/provider/JCERSAPrivateCrtKey.java b/prov/src/main/java/org/bouncycastle/jce/provider/JCERSAPrivateCrtKey.java
index 40f007f3d7..27fc10cfa2 100644
--- a/prov/src/main/java/org/bouncycastle/jce/provider/JCERSAPrivateCrtKey.java
+++ b/prov/src/main/java/org/bouncycastle/jce/provider/JCERSAPrivateCrtKey.java
@@ -224,7 +224,7 @@ public boolean equals(Object o)
 
     public String toString()
     {
-        StringBuffer    buf = new StringBuffer();
+        StringBuilder   buf = new StringBuilder();
         String          nl = Strings.lineSeparator();
 
         buf.append("RSA Private CRT Key").append(nl);
diff --git a/prov/src/test/java/org/bouncycastle/jce/provider/test/BlockCipherTest.java b/prov/src/test/java/org/bouncycastle/jce/provider/test/BlockCipherTest.java
index 0f3bf103df..d281ddc174 100644
--- a/prov/src/test/java/org/bouncycastle/jce/provider/test/BlockCipherTest.java
+++ b/prov/src/test/java/org/bouncycastle/jce/provider/test/BlockCipherTest.java
@@ -970,7 +970,7 @@ else if (algorithm.startsWith("RC5"))
 
         try
         {
-            if (algorithm.indexOf("CCM") < 0 && algorithm.indexOf("Threefish") < 0 && algorithm.indexOf("PGPCFB") < 0)
+            if (!algorithm.contains("CCM") && !algorithm.contains("Threefish") && !algorithm.contains("PGPCFB"))
             {
                 //
                 // short buffer on update test
@@ -1671,7 +1671,7 @@ private void testIncorrectCipherModes()
             }
             catch (NoSuchAlgorithmException e)
             {
-                if (!(e.getMessage().indexOf("can't support mode ") >= 0))      // old JVM
+                if (!e.getMessage().contains("can't support mode "))      // old JVM
                 {
                     isEquals("1 got: " + e.getMessage(), "No such algorithm: AES/" + cipherModes[i] + "NOT_REAL/NoPadding", e.getMessage());
                 }
@@ -1695,7 +1695,7 @@ private void testIncorrectCipherModes()
             }
             catch (NoSuchAlgorithmException e)
             {
-                if (!(e.getMessage().indexOf("can't support mode ") >= 0))      // old JVM
+                if (!e.getMessage().contains("can't support mode "))      // old JVM
                 {
                     isEquals("2 got: " + e.getMessage(), "No such algorithm: AES/" + cipherModes[i] + "256/NoPadding", e.getMessage());
                 }
@@ -1719,7 +1719,7 @@ private void testIncorrectCipherModes()
             }
             catch (NoSuchAlgorithmException e)
             {
-                if (!(e.getMessage().indexOf("can't support mode ") >= 0))      // old JVM
+                if (!e.getMessage().contains("can't support mode "))      // old JVM
                 {
                     isEquals("3 got: " + e.getMessage(), "No such algorithm: AES/" + cipherModes[i] + "2/NoPadding", e.getMessage());
                 }
@@ -1743,7 +1743,7 @@ private void testIncorrectCipherModes()
             }
             catch (NoSuchAlgorithmException e)
             {
-                if (!(e.getMessage().indexOf("can't support mode ") >= 0))      // old JVM
+                if (!e.getMessage().contains("can't support mode "))      // old JVM
                 {
                     isEquals("No such algorithm: AES/" + cipherModes[i] + "9/NoPadding", e.getMessage());
                 }
diff --git a/prov/src/test/java/org/bouncycastle/jce/provider/test/CertPathValidatorTest.java b/prov/src/test/java/org/bouncycastle/jce/provider/test/CertPathValidatorTest.java
index dbcedc5f2a..6f4795fbc7 100644
--- a/prov/src/test/java/org/bouncycastle/jce/provider/test/CertPathValidatorTest.java
+++ b/prov/src/test/java/org/bouncycastle/jce/provider/test/CertPathValidatorTest.java
@@ -1393,7 +1393,7 @@ private int calculateHashCode()
 
         public String toString()
         {
-            StringBuffer buf = new StringBuffer();
+            StringBuilder buf = new StringBuilder();
             String nl = Strings.lineSeparator();
 
             buf.append("  [0]         Version: ").append(this.getVersion()).append(nl);
diff --git a/prov/src/test/java/org/bouncycastle/jce/provider/test/CertUniqueIDTest.java b/prov/src/test/java/org/bouncycastle/jce/provider/test/CertUniqueIDTest.java
index b61018bc98..a1dc5a5f79 100644
--- a/prov/src/test/java/org/bouncycastle/jce/provider/test/CertUniqueIDTest.java
+++ b/prov/src/test/java/org/bouncycastle/jce/provider/test/CertUniqueIDTest.java
@@ -129,7 +129,7 @@ public void checkCreation1()
 
   private String arrayToString(boolean[] array)
   {
-      StringBuffer b = new StringBuffer();
+      StringBuilder b = new StringBuilder();
 
       for (int i = 0; i != array.length; i++)
       {
diff --git a/prov/src/test/java/org/bouncycastle/jce/provider/test/CipherStreamTest2.java b/prov/src/test/java/org/bouncycastle/jce/provider/test/CipherStreamTest2.java
index 99f8c89c65..0bd996bc91 100644
--- a/prov/src/test/java/org/bouncycastle/jce/provider/test/CipherStreamTest2.java
+++ b/prov/src/test/java/org/bouncycastle/jce/provider/test/CipherStreamTest2.java
@@ -38,7 +38,7 @@ private void testModes(String algo, String[] transforms, boolean authenticated)
             String transform = transforms[i];
             String cipherName = algo + transform;
 
-            boolean cts = transform.indexOf("CTS") > -1;
+            boolean cts = transform.contains("CTS");
             if (cts && streamSize < Cipher.getInstance(cipherName, "BC").getBlockSize())
             {
                 continue;
diff --git a/tls/src/main/java/org/bouncycastle/tls/crypto/impl/jcajce/JcaTlsCertificate.java b/tls/src/main/java/org/bouncycastle/tls/crypto/impl/jcajce/JcaTlsCertificate.java
index 9f14399762..424bc6838d 100644
--- a/tls/src/main/java/org/bouncycastle/tls/crypto/impl/jcajce/JcaTlsCertificate.java
+++ b/tls/src/main/java/org/bouncycastle/tls/crypto/impl/jcajce/JcaTlsCertificate.java
@@ -368,7 +368,7 @@ PublicKey getPubKeyEd25519() throws IOException
         if (!"Ed25519".equals(publicKey.getAlgorithm()))
         {
             // Oracle provider (Java 15+) returns the key as an EdDSA one
-            if (!("EdDSA".equals(publicKey.getAlgorithm()) && publicKey.toString().indexOf("Ed25519") >= 0))
+            if (!("EdDSA".equals(publicKey.getAlgorithm()) && publicKey.toString().contains("Ed25519")))
             {
                 throw new TlsFatalAlert(AlertDescription.certificate_unknown, "Public key not Ed25519");
             }
@@ -382,7 +382,7 @@ PublicKey getPubKeyEd448() throws IOException
         if (!"Ed448".equals(publicKey.getAlgorithm()))
         {
             // Oracle provider (Java 15+) returns the key as an EdDSA one
-            if (!("EdDSA".equals(publicKey.getAlgorithm()) && publicKey.toString().indexOf("Ed448") >= 0))
+            if (!("EdDSA".equals(publicKey.getAlgorithm()) && publicKey.toString().contains("Ed448")))
             {
                 throw new TlsFatalAlert(AlertDescription.certificate_unknown, "Public key not Ed448");
             }
diff --git a/util/src/main/java/org/bouncycastle/asn1/dvcs/DVCSCertInfo.java b/util/src/main/java/org/bouncycastle/asn1/dvcs/DVCSCertInfo.java
index ce5ecd5ea1..c29dfe64aa 100644
--- a/util/src/main/java/org/bouncycastle/asn1/dvcs/DVCSCertInfo.java
+++ b/util/src/main/java/org/bouncycastle/asn1/dvcs/DVCSCertInfo.java
@@ -190,7 +190,7 @@ public ASN1Primitive toASN1Primitive()
 
     public String toString()
     {
-        StringBuffer s = new StringBuffer();
+        StringBuilder s = new StringBuilder();
 
         s.append("DVCSCertInfo {\n");
 
diff --git a/util/src/main/java/org/bouncycastle/asn1/dvcs/DVCSRequestInformation.java b/util/src/main/java/org/bouncycastle/asn1/dvcs/DVCSRequestInformation.java
index e0026cba21..1606528e14 100644
--- a/util/src/main/java/org/bouncycastle/asn1/dvcs/DVCSRequestInformation.java
+++ b/util/src/main/java/org/bouncycastle/asn1/dvcs/DVCSRequestInformation.java
@@ -184,7 +184,7 @@ public ASN1Primitive toASN1Primitive()
     public String toString()
     {
 
-        StringBuffer s = new StringBuffer();
+        StringBuilder s = new StringBuilder();
 
         s.append("DVCSRequestInformation {\n");