How to “do something” on Swing component resizing?

Question

I\'ve a class which extends JPanel. I overwrote protected void paintComponent(Graphics g).

There is a variable which has to be recalculate

Answer 1

This simple example is drawing a red circle in the resized frame....

import java.awt.*;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import javax.swing.*;
import java.awt.geom.*;

public class RedCircle extends JFrame implements ComponentListener {
     int getWidth;
     int getHeight;
     
      public RedCircle() {
        super("Red Circle");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        addComponentListener(this);             
        pack();
        setVisible(true);
    }
    
      public void componentResized(ComponentEvent e) {
            getWidth = e.getComponent().getWidth();
            getHeight = e.getComponent().getHeight();
            
            Panel pane = new Panel(getWidth,getHeight);
            
            add(pane);
      }
    
   
    public static void main(String[] args) {
        
         RedCircle rc = new RedCircle();
    }
    

 
 public void componentMoved(ComponentEvent e) {
       
    }

    
    public void componentShown(ComponentEvent e) {
     
    }

    
    public void componentHidden(ComponentEvent e) {
    
    }


}


class Panel extends JPanel {
    int panelWidth;
    int panelHeight;
    
    public Panel(Integer getWidth,Integer getHeight) {
       
    panelWidth = getWidth;
    panelHeight = getHeight;
    
    }
    
public void paintComponent(Graphics comp) {
        super.paintComponent(comp);
        Graphics2D comp2D = (Graphics2D) comp;
       
        int realWidth = panelWidth - 17;
        int realHeight = panelHeight - 40;
       
        float Height = (realHeight);
        float Width = (realWidth);
        
    // draw the Red Circle
        comp2D.setColor(Color.red);
        Ellipse2D.Float redCircle = new Ellipse2D.Float(0F, 0F, Width, Height);
        comp2D.fill(redCircle);
    }
}