This occurs because of the way that anonymous classes are implemented. You can see this if you make a slight change to the code and then decompile: final Runnable other = null; final Runnable example = new Runnable() { @Override public void run() { System.out.println(other); } }; i.e. make the anonymous class refer to a … Read more
One advantage of anonymous inner classes is that no one can ever use it anywhere else, whereas a named inner class can be used (if only by the class that created it if made private). It’s a small distinction, but it does mean that you can protect an inner class from being accidentally used elsewhere. … Read more
Effectively final means that it is never changed after getting the initial value. A simple example: public void myMethod() { int a = 1; System.out.println(“My effectively final variable has value: ” + a); } Here, a is not declared final, but it is considered effectively final since it is never changed. Starting with Java 8, … Read more
As of JDK 18, no. JDK 18 omits enclosing instance fields from inner classes that don’t use it. However, prior to JDK 18, yes, instances of anonymous inner classes hold on to a reference to their enclosing instances even if these references are never actually used. For example, this code: public class Outer { public … Read more
Container.this.select();
Java doesn’t know that doWork is going to be synchronous and that the stack frame that result is in will still be there. You need to alter something that isn’t in the stack. I think this would work final Long[] result = new Long[1]; and then result[0] = st.getLong(4); in execute(). At the end, you … Read more
Note that the wording in the JLS of that particular section has changed significantly since then. It now (JLS 11) reads: 15.9.5. Anonymous Class Declarations: An anonymous class is never final (ยง8.1.1.2). The fact that an anonymous class is not final is relevant in casting, in particular the narrowing reference conversion allowed for the cast … Read more
Joshua Bloch writes in his book Effective Java, 2nd Edition, Item 74: Inner classes should not implement Serializable. They use compiler-generated synthetic fields to store references to enclosing instances and to store values of local variables from enclosing scopes. How these fields correspond to the class definition is unspecified, as are the names of anonymous … Read more
Anonymous classes must extend or implement something, like any other Java class, even if it’s just java.lang.Object. For example: Runnable r = new Runnable() { public void run() { … } }; Here, r is an object of an anonymous class which implements Runnable. An anonymous class can extend another class using the same syntax: … Read more
Yes, by adding an initializer method that returns ‘this’, and immediately calling that method: int myVariable = 1; myButton.addActionListener(new ActionListener() { private int anonVar; public void actionPerformed(ActionEvent e) { // How would one access myVariable here? // It’s now here: System.out.println(“Initialized with value: ” + anonVar); } private ActionListener init(int var){ anonVar = var; return … Read more