Java 8 Interface with state

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package ch.claude_martin.java8.mixins;

import java.util.IdentityHashMap;

public interface FooBar {
  static class Data {
    int foo = 0;
    String bar = "";
  }
  // TODO : Should be some kind of WeakIdentityHashMap!
  final static IdentityHashMap<FooBar, Data> _map = new IdentityHashMap<>();

  static Data get(FooBar foobar) {
    return _map.computeIfAbsent(foobar, x -> new Data());
  }

  default int getFoo() {
    return get(this).foo;
  }

  default void setFoo(int foo) {
    get(this).foo = foo;
  }

  default String getBar() {
    return get(this).bar;
  }

  default void setBar(String bar) {
    get(this).bar = bar;
  }

}
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package ch.claude_martin.java8.mixins;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class MixinUsage {

    public static void main(String... args) {
        MyActionListener foobar = new MyActionListener();
        foobar.setFoo(42);
        foobar.setBar("Hello");
        foobar.actionPerformed(null);
    }

    static class MyActionListener implements ActionListener, FooBar {

        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("foo: " + getFoo());
            System.out.println("bar: " + getBar());
        }

    }
}


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