Question

My program code is here:

package Chapter12;

import java.awt.*;
import javax.swing.*;

public class Pv2 extends JPanel {

    public static void main (String []args){

        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(500,500);
        frame.setVisible(true);
        frame.setContentPane(new Pv2());




    }

    @Override
    public void paintComponent(Graphics g){

        Graphics2D g2 = (Graphics2D) g;
    }



}

Eclipse shows this error when I’m trying to compile the code.

Cannot cast from Graphics to Graphics2D

This error occurs on this line :

Graphics2D g2 = (Graphics2D) g;

Tried jre 1.6 and jre 1.7 – the same thing. Why the cast isn’t allowed? I even tried to download some prepared codes and the error was the same.

Answer 1

You code is not broken and this cast is surely possible. The following code works:

import java.awt.*;
import javax.swing.*;

public class Pv2 extends JPanel {
    public static void main (String []args){
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(200,200);
        frame.setVisible(true);
        frame.setContentPane(new Pv2());
    }
    public void paintComponent(Graphics g){
        Graphics2D g2 = (Graphics2D) g;
        g2.drawLine(0,0, getWidth(), getHeight());
    }
}

One of the possible explanations, you have the class named exactly Graphics or Graphics2D in the same package (Chapter12). Then, with imports as you have, this class will have priority; if it is not compatible, the cast will be rejected by the compiler. I was able to reproduce this by crating the empty class in the same package and naming it Graphics2D.

To solve, use explicit imports: replace your import statements by

import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JFrame;
import javax.swing.JPanel;

This will tell the compiler which Graphics and Graphics2D do you mean. Even with confusing Graphics2D class, I do not longer see the error after rewriting imports as shown.