Java内联接口实现，变量和方法调用

Question

In Java, why can I do this

new java.awt.event.WindowAdapter() {
    public void windowClosing(java.awt.event.WindowEvent evt) {
        screenClosed();
    }
}

// ...

public void screenClosed() {
    running = false;
}

but not

new java.awt.event.WindowAdapter() {
    public void windowClosing(java.awt.event.WindowEvent evt) {
        running = false;
    }
}

?

Answer 1

I'm guessing that running is a local variable, not a field in your second example, and you have to make it a field with the screenClosed method to make it work? It's hard to tell from your code sample.

If so: inner classes such as local or anonymous classes require that (local) variables are marked final (they are constants). This is due to the way the compiler constructs the class by passing the variable as an argument to the compiler-created constructor, and then storing it as a field in the compiler-generated class.

You can get around this limitation by declaring the local variable as:

final boolean[] running = new boolean[]{true};

and then setting running[0] = false instead.