diff --git a/src/main/org/apache/tools/ant/taskdefs/AntStructure.java b/src/main/org/apache/tools/ant/taskdefs/AntStructure.java
index 10473d3df..dcc787d57 100644
--- a/src/main/org/apache/tools/ant/taskdefs/AntStructure.java
+++ b/src/main/org/apache/tools/ant/taskdefs/AntStructure.java
@@ -19,12 +19,9 @@
 package org.apache.tools.ant.taskdefs;
 
 import java.io.File;
-import java.io.FileWriter;
 import java.io.IOException;
-import java.io.OutputStream;
 import java.io.OutputStreamWriter;
 import java.io.PrintWriter;
-import java.io.UnsupportedEncodingException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.util.ArrayList;
@@ -43,7 +40,6 @@ import org.apache.tools.ant.Task;
 import org.apache.tools.ant.TaskContainer;
 import org.apache.tools.ant.types.EnumeratedAttribute;
 import org.apache.tools.ant.types.Reference;
-import org.apache.tools.ant.util.FileUtils;
 
 /**
  * Creates a partial DTD for Ant from the currently known tasks.
diff --git a/src/main/org/apache/tools/ant/taskdefs/optional/junit/JUnit4TestMethodAdapter.java b/src/main/org/apache/tools/ant/taskdefs/optional/junit/JUnit4TestMethodAdapter.java
index b1a64017e..2571c10aa 100644
--- a/src/main/org/apache/tools/ant/taskdefs/optional/junit/JUnit4TestMethodAdapter.java
+++ b/src/main/org/apache/tools/ant/taskdefs/optional/junit/JUnit4TestMethodAdapter.java
@@ -111,18 +111,7 @@ public class JUnit4TestMethodAdapter implements Test {
 
     @Override
     public String toString() {
-        String testClassName = testClass.getName();
-        StringBuilder buf = new StringBuilder(testClassName.length()
-                                              + 12 * methodNames.length)
-                            .append(':');
-        if (methodNames.length != 0) {
-            buf.append(methodNames[0]);
-            for (int i = 1; i < methodNames.length; i++) {
-                buf.append(',')
-                   .append(methodNames[i]);
-            }
-        }
-        return buf.toString();
+        return ":" + String.join(",", methodNames);
     }
 
     private static final class MultipleMethodsFilter extends Filter {
@@ -166,10 +155,7 @@ public class JUnit4TestMethodAdapter implements Test {
                 buf.append("No methods");
             } else {
                 buf.append(methodNames.length == 1 ? "Method " : "Methods ");
-                for (String methodName : methodNames) {
-                    buf.append(methodName).append(',');
-                }
-                buf.setLength(buf.length() - 1);
+                buf.append(String.join(",", methodNames));
             }
             buf.append('(').append(testClass.getName()).append(')');
             return buf.toString();
diff --git a/src/main/org/apache/tools/ant/taskdefs/optional/junit/JUnitTest.java b/src/main/org/apache/tools/ant/taskdefs/optional/junit/JUnitTest.java
index e041e3069..1a0de4b38 100644
--- a/src/main/org/apache/tools/ant/taskdefs/optional/junit/JUnitTest.java
+++ b/src/main/org/apache/tools/ant/taskdefs/optional/junit/JUnitTest.java
@@ -222,18 +222,7 @@ public class JUnitTest extends BaseTest implements Cloneable {
      */
     String getMethodsString() {
         if (methodsList == null && methodsSpecified) {
-            if (methods.length == 0) {
-                methodsList = "";
-            } else if (methods.length == 1) {
-                methodsList = methods[0];
-            } else {
-                StringBuilder buf = new StringBuilder(methods.length * 16);
-                buf.append(methods[0]);
-                for (int i = 1; i < methods.length; i++) {
-                    buf.append(',').append(methods[i]);
-                }
-                methodsList = buf.toString();
-            }
+            methodsList = methods.length == 0 ? "" : String.join(",", methods);
         }
         return methodsList;
     }
diff --git a/src/main/org/apache/tools/ant/taskdefs/optional/net/FTP.java b/src/main/org/apache/tools/ant/taskdefs/optional/net/FTP.java
index aa69cf7e1..901ff06a8 100644
--- a/src/main/org/apache/tools/ant/taskdefs/optional/net/FTP.java
+++ b/src/main/org/apache/tools/ant/taskdefs/optional/net/FTP.java
@@ -244,11 +244,7 @@ public class FTP extends Task implements FTPTaskConfig {
          */
         @Override
         public String getParent() {
-            StringBuilder result = new StringBuilder();
-            for (int i = 0; i < parts.length - 1; i++) {
-                result.append(File.separatorChar).append(parts[i]);
-            }
-            return result.toString();
+            return File.separator + String.join(File.separator, parts);
         }
 
 
diff --git a/src/main/org/apache/tools/ant/types/DirSet.java b/src/main/org/apache/tools/ant/types/DirSet.java
index d71ae3383..855d5c3d4 100644
--- a/src/main/org/apache/tools/ant/types/DirSet.java
+++ b/src/main/org/apache/tools/ant/types/DirSet.java
@@ -20,7 +20,6 @@ package org.apache.tools.ant.types;
 
 import java.util.Iterator;
 
-import org.apache.tools.ant.DirectoryScanner;
 import org.apache.tools.ant.types.resources.FileResourceIterator;
 
 /**