Graphics In Java

Graphics:

Window is like a painter’s canvas.

App must paint its window contents

Java components paint themselves

Anything else:  Programmer

Painting a Swing Component:

Three methods are at the heart of painting a swing component

paintComponent()

paintBorder()

paintChildren()

The three methods are invoked in this order:

paintComponent — The main method for painting. By default, it first paints the background. Then it performs any custom painting.

paintBorder — Tells the component's border (if any) to paint. Do not invoke or override this method.

paintChildren — Tells any components contained by this component to paint themselves. Do not invoke or override this method

Yours' Painting Strategy:

Steps

Subclass JPanel

public class MyPanel extends JPanel

Override the public void paintComponent(Graphics g) method

Inside method using graphics object g and,  do whatever drawing you want to do.

Install that JPanel inside a JFrame

When frame becomes visible through the paintChildren() method your panel become visible

To become visible your panel will call paintComponent() method which will do your custom drawing

For example:

//PainPanel.java

import java.awt.*;

import javax.swing.*;

public class PaintPanel extends JPanel {

         

    public void paintComponent(Graphics g) {

                

          super.paintComponent(g);//For calling super class constructor to erase behavior

         

        Graphics2D g2D = (Graphics2D)g;   

        g2D.drawRect(20,20,20,20);

        g2D.setColor(Color.blue);

      

        g2D.fillOval(50,50,20,20);

        g2D.drawString("Hello World", 120, 50);

   }

}

//PaintOnFrame.java

import java.awt.*;

import javax.swing.*;

public class PaintOnFrame {

      

       JFrame myFrame = null;

       PaintPanel pp = null; //yours PaintPanel objectRefernce

       Container con = null;

      

       public PaintOnFrame() {

      

              myFrame = new JFrame();

              con = myFrame.getContentPane();

              con.setLayout(new BorderLayout());

             

              //Here is creating PaintPanel Object

              pp = new PaintPanel();

              con.add(pp);//now adding that PaintPanel object which shows your painting

             

              myFrame.setSize(200,200);  

              myFrame.setVisible(true);

              myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  

       }

      

       public static void main(String[] args) {

                new PaintOnFrame();

       }

}

Animation:

Constantly need to call paintComponent() and draw the shape at new place (new co-ordinates).

Painting is managed by system and calling paintComponent() directly is not recommended at all.

Use Repaint() mechanism.

//AnimatePanel.java

import java.awt.*;

import javax.swing.*;

public class AnimatePanel extends JPanel {

         

   int mX = 200;

   int mY = 0;

  

          public void paintComponent(Graphics g) {

                 super.paintComponent(g);

                 Graphics2D g2 = (Graphics2D)g;

                 g2.fillOval(mX, mY, 20, 20);

          }

}

//AnimateOnFrame.java

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class AnimateOnFrame implements ActionListener {

      

       JFrame myFrame = null;

       PaintPanel pp = null;

       Container con = null;

       int x = 5 , y = 3;

       public AnimateOnFrame() {

      

              myFrame = new JFrame();

              con = myFrame.getContentPane();

              con.setLayout(new BorderLayout());

             

              pp = new PaintPanel();

              con.add(pp);

             

              myFrame.setSize(400,400);  

              myFrame.setVisible(true);

              myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  

             

               Timer t = new Timer (5, this);

               t.start();

       }

      

       public void actionPerformed(ActionEvent e) {

       

              if (myFrame.getWidth()-40 == pp.mX)

                      x= -5;

              if (myFrame.getHeight()-40 == pp.mY)

                     y= -3;

              if (pp.mX == 0 )

                     x = 5;

              if (pp.mY == 0 )      

                     y = 3;

              pp.mX += x;

              pp.mY += y;       

              pp.repaint();

       }

      

       public static void main(String[] args) {

              new AnimateOnFrame();

       }

}