Synchronized fields ought to be final

src/main/org/apache/tools/ant/ComponentHelper.java

@@ -60,7 +60,7 @@ import org.apache.tools.ant.util.FileUtils;
  */
 public class ComponentHelper  {
     /** Map of component name to lists of restricted definitions */
-    private Map<String, List<AntTypeDefinition>> restrictedDefinitions = new HashMap<>();
+    private final Map<String, List<AntTypeDefinition>> restrictedDefinitions = new HashMap<>();
 
     /** Map from component name to anttypedefinition */
     private final Hashtable<String, AntTypeDefinition> antTypeTable = new Hashtable<>();

src/main/org/apache/tools/ant/PropertyHelper.java

@@ -238,21 +238,21 @@ public class PropertyHelper implements GetProperty {
     private final Hashtable<Class<? extends Delegate>, List<Delegate>> delegates = new Hashtable<>();
 
     /** Project properties map (usually String to String). */
-    private Hashtable<String, Object> properties = new Hashtable<>();
+    private final Hashtable<String, Object> properties = new Hashtable<>();
 
     /**
      * Map of "user" properties (as created in the Ant task, for example).
      * Note that these key/value pairs are also always put into the
      * project properties, so only the project properties need to be queried.
      */
-    private Hashtable<String, Object> userProperties = new Hashtable<>();
+    private final Hashtable<String, Object> userProperties = new Hashtable<>();
 
     /**
      * Map of inherited "user" properties - that are those "user"
      * properties that have been created by tasks and not been set
      * from the command line or a GUI tool.
      */
-    private Hashtable<String, Object> inheritedProperties = new Hashtable<>();
+    private final Hashtable<String, Object> inheritedProperties = new Hashtable<>();
 
     /**
      * Default constructor.

src/main/org/apache/tools/ant/taskdefs/JDBCTask.java

@@ -97,7 +97,7 @@ public abstract class JDBCTask extends Task {
      * getting an OutOfMemoryError when calling this task
      * multiple times in a row.
      */
-    private static Hashtable<String, AntClassLoader> LOADER_MAP = new Hashtable<>(HASH_TABLE_SIZE);
+    private static final Hashtable<String, AntClassLoader> LOADER_MAP = new Hashtable<>(HASH_TABLE_SIZE);
 
     private boolean caching = true;
 

src/main/org/apache/tools/ant/taskdefs/ProcessDestroyer.java

@@ -31,7 +31,7 @@ import java.util.Set;
 class ProcessDestroyer implements Runnable {
     private static final int THREAD_DIE_TIMEOUT = 20000;
 
-    private Set<Process> processes = new HashSet<>();
+    private final Set<Process> processes = new HashSet<>();
     // methods to register and unregister shutdown hooks
     private Method addShutdownHookMethod;
     private Method removeShutdownHookMethod;