Java Swing How to - Do Proportional resizing of JFrame

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Question

We would like to know how to do Proportional resizing of JFrame.

Answer

import java.awt.Dimension;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.util.HashSet;
import java.util.Set;
//from  w w w  .  j av a  2s . c o m
import javax.swing.JFrame;

public class Main extends JFrame {
  State state;
  Set<StateListener> listeners = new HashSet<StateListener>();

  public Main() {
    state = new State();
    addComponentListener(new ComponentAdapter() {
      @Override
      public void componentResized(ComponentEvent e) {
        state.setSize(getSize(), true);
      }

      @Override
      public void componentMoved(ComponentEvent e) {
      }
      @Override
      public void componentShown(ComponentEvent e) {
      }
      @Override
      public void componentHidden(ComponentEvent e) {
      }
    });
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);
  }

  private void addListener(StateListener sl) {
    listeners.add(sl);
  }

  public void associateWith(Main other) {
    other.addListener(new MirrorStateListener());
  }

  public static void main(String[] args) {
    Main f1 = new Main();
    Main f2 = new Main();
    f1.associateWith(f2);
    f2.associateWith(f1);
    f1.setSize(300, 300);
    f2.setLocation(600, 10);
  }
  class State {
    Dimension size;
    public void setSize(Dimension newSize, boolean fireEvent) {
      if (newSize.equals(size)) {
        return;
      }
      size = newSize;
      Main.this.setSize(size);
      if (fireEvent) {
        for (StateListener sl : listeners) {
          sl.sizeChanged(size);
        }
      }
    }
  }

  class MirrorStateListener implements StateListener {
    @Override
    public void sizeChanged(Dimension newSize) {
      state.setSize(newSize, false);
    }
  }
}

interface StateListener {
  void sizeChanged(Dimension newSize);
}

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