Java language level syntactic sugaring

Non-functional change - make use of new Java language features available up to Java 17 LTS

- Use String.repeat()
- Replace statements with enhanced switch
- Use pattern variable
- Convert to enhanced for-loop
- Prefer StringBuilder over StringBuffer
- Remove unnecessary boxing/unboxing
- Use Objects.equals() rather than equals() expression
- Replace explicit types by diamond operator
- Use lambdas for anonymous types
- Use Comparator combinator
- Introduce method references for lambdas
- Change statement to expression lambdas
- Check for null using method call

dbus-java-core/src/main/java/org/freedesktop/dbus/DBusMap.java

@@ -56,7 +56,7 @@ public Set<Map.Entry<K, V>> entrySet() {
     @SuppressWarnings("unchecked")
     public V get(Object _key) {
         for (Object[] entry : entries) {
-            if (_key == entry[0] || _key != null && _key.equals(entry[0])) {
+            if (Objects.equals(_key, entry[0])) {
                 return (V) entry[1];
             }
         }

dbus-java-core/src/main/java/org/freedesktop/dbus/DBusMatchRule.java

@@ -255,10 +255,9 @@ public boolean equals(Object _obj) {
         if (this == _obj) {
             return true;
         }
-        if (!(_obj instanceof DBusMatchRule)) {
+        if (!(_obj instanceof DBusMatchRule other)) {
             return false;
         }
-        DBusMatchRule other = (DBusMatchRule) _obj;
         return Objects.equals(iface, other.iface) && Objects.equals(member, other.member)
                 && Objects.equals(object, other.object) && Objects.equals(source, other.source)
                 && Objects.equals(type, other.type);

dbus-java-core/src/main/java/org/freedesktop/dbus/MethodTuple.java

@@ -13,11 +13,7 @@ public class MethodTuple {
 
     public MethodTuple(String _name, String _sig) {
         name = _name;
-        if (null != _sig) {
-            sig = _sig;
-        } else {
-            sig = "";
-        }
+        sig = Objects.requireNonNullElse(_sig, "");
         logger.trace("new MethodTuple({}, {})", name, sig);
     }
 
@@ -31,10 +27,9 @@ public boolean equals(Object _obj) {
         if (this == _obj) {
             return true;
         }
-        if (!(_obj instanceof MethodTuple)) {
+        if (!(_obj instanceof MethodTuple other)) {
             return false;
         }
-        MethodTuple other = (MethodTuple) _obj;
         return Objects.equals(name, other.name) && Objects.equals(sig, other.sig);
     }
 

dbus-java-core/src/main/java/org/freedesktop/dbus/RemoteInvocationHandler.java

@@ -54,7 +54,7 @@ public Object invoke(Object _proxy, Method _method, Object[] _args) throws Throw
         } else if (_method.getName().equals("equals")) {
             try {
                 if (1 == _args.length) {
-                    return Boolean.valueOf(_args[0] != null && remote.equals(((RemoteInvocationHandler) Proxy.getInvocationHandler(_args[0])).remote));
+                    return _args[0] != null && remote.equals(((RemoteInvocationHandler) Proxy.getInvocationHandler(_args[0])).remote);
                 }
             } catch (IllegalArgumentException _exIa) {
                 return Boolean.FALSE;
@@ -211,16 +211,16 @@ public static Object executeRemoteMethod(final RemoteObject _ro, final Method _m
         }
 
         switch (_syncmethod) {
-            case CALL_TYPE_ASYNC:
+            case CALL_TYPE_ASYNC -> {
                 _conn.sendMessage(call);
                 return new DBusAsyncReply<>(call, _m, _conn);
-            case CALL_TYPE_CALLBACK:
+            }
+            case CALL_TYPE_CALLBACK -> {
                 _conn.queueCallback(call, _m, _callback);
                 _conn.sendMessage(call);
                 return null;
-            case CALL_TYPE_SYNC:
-                _conn.sendMessage(call);
-                break;
+            }
+            case CALL_TYPE_SYNC -> _conn.sendMessage(call);
         }
 
         // get reply

dbus-java-core/src/main/java/org/freedesktop/dbus/RemoteObject.java

@@ -17,10 +17,9 @@ public RemoteObject(String _busname, String _objectpath, Class<? extends DBusInt
 
     @Override
     public boolean equals(Object _o) {
-        if (!(_o instanceof RemoteObject)) {
+        if (!(_o instanceof RemoteObject them)) {
             return false;
         }
-        RemoteObject them = (RemoteObject) _o;
 
         if (!them.objectpath.equals(this.objectpath)) {
             return false;

dbus-java-core/src/main/java/org/freedesktop/dbus/StructHelper.java

@@ -8,6 +8,7 @@
 import java.lang.reflect.Field;
 import java.lang.reflect.InvocationTargetException;
 import java.util.*;
+import java.util.function.IntFunction;
 
 /**
  * Helper util to create {@link Struct} subclasses when receiving it from DBus.
@@ -100,7 +101,7 @@ public static <T extends Struct> void convertToStructCollection(Collection<Objec
 
         Class<?>[] constructorArgClasses = Arrays.stream(_structType.getDeclaredFields())
             .filter(f -> f.isAnnotationPresent(Position.class))
-            .sorted((f1, f2) -> Integer.compare(f1.getAnnotation(Position.class).value(), f2.getAnnotation(Position.class).value()))
+            .sorted(Comparator.comparingInt(f -> f.getAnnotation(Position.class).value()))
             .map(Field::getType)
             .toArray(Class[]::new);
 
@@ -137,7 +138,7 @@ public static <T extends Struct> T createStructFromVariant(Variant<?> _variant,
         }
 
         if (_variant.getType() instanceof DBusStructType && _variant.getValue() instanceof Object[]) {
-            Class<?>[] argTypes = Arrays.stream((Object[]) _variant.getValue()).map(Object::getClass).toArray(size -> new Class<?>[size]);
+            Class<?>[] argTypes = Arrays.stream((Object[]) _variant.getValue()).map(Object::getClass).toArray((IntFunction<Class<?>[]>) Class[]::new);
             return createStruct(argTypes, _variant.getValue(), _structClass);
         }
 

dbus-java-core/src/main/java/org/freedesktop/dbus/bin/DBusDaemon.java

@@ -869,10 +869,9 @@ public boolean equals(Object _obj) {
             if (this == _obj) {
                 return true;
             }
-            if (!(_obj instanceof Pair)) {
+            if (!(_obj instanceof Pair<?, ?> other)) {
                 return false;
             }
-            Pair<?, ?> other = (Pair<?, ?>) _obj;
             return Objects.equals(first, other.first) && Objects.equals(second, other.second);
         }
 

dbus-java-core/src/main/java/org/freedesktop/dbus/connections/AbstractConnection.java

@@ -412,7 +412,7 @@ private static Class<?>[] createTypesArray(Object... _parameters) {
             return null;
         }
         return Arrays.stream(_parameters)
-                .filter(p -> p != null) // do no try to convert null values to concrete class
+                .filter(Objects::nonNull) // do no try to convert null values to concrete class
                 .map(p -> {
                     if (List.class.isAssignableFrom(p.getClass())) { // turn possible List subclasses (e.g. ArrayList) to interface class List
                         return List.class;