Desenhos simples

Os arquivos abaixo foram extraídos do Livro:

An Introduction to Graphical User Interfaces with Java Swing

package its.SimpleGraphics;

/**

* Example program for Introduction to Swing

* @author Paul Fischer, IMM, DTU

* @version 1.0

*/

public class SimpleGraphicsDriver

{

public SimpleGraphicsDriver()

{

SimpleGraphicsFrame SGF = new SimpleGraphicsFrame();

SGF.showIt();

}

public static void main(String[] args)

{

SimpleGraphicsDriver sgt = new SimpleGraphicsDriver();

}

}

package its.SimpleGraphics;

import its.SimpleFrame.SimpleFrame;

import java.awt.BorderLayout;

/**

* Example program for Introduction to Swing

* @author Paul Fischer, IMM, DTU

* @version 1.0

*/

public class SimpleGraphicsFrame extends SimpleFrame

{

public SimpleGraphicsFrame()

{

this.setTitle("Simple Graphics");

SimpleGraphicsPanel SGP = new SimpleGraphicsPanel();

this.getContentPane().add(SGP,BorderLayout.CENTER);

pack();

}

}

package its.SimpleGraphics;

import java.awt.*;

import javax.swing.JPanel;

/**

* Example program for Introduction to Swing

* @author Paul Fischer, IMM, DTU

* @version 1.0

*/

public class SimpleGraphicsPanel extends JPanel

{

public SimpleGraphicsPanel()

{

this.setBackground(Color.white);

this.setPreferredSize(new Dimension(300,300));

}

public void paintComponent(Graphics g)

{

super.paintComponent(g);

g.setColor(Color.black);

g.drawLine(10,10,100,100);

g.setColor(Color.red);

g.drawLine(10,100,100,10);

g.setColor(Color.green);

g.drawOval(120,60,70,40);

g.setColor(Color.yellow);

g.fillOval(230,150,30,30);

g.setColor(Color.red);

g.fillOval(245,150,30,30);

g.setColor(Color.black);

g.fillOval(238,160,30,30);

g.setColor(Color.cyan);

g.fillOval(10,120,100,60);

g.setColor(this.getBackground());

g.fillOval(50,140,100,60);

g.setColor(Color.blue);

g.drawString("Swing is nice.",100,200);

}

}

esboço:

O programa abaixo extraido do livro

Java for Students tem erros conceituais:

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class java4students extends JFrame implements ActionListener {

private JButton button;

private JPanel panel;

public static void main(String[] arg ){

java4students frame = new java4students();

frame.setSize(400, 300);

frame.createGUI();

frame.setVisible(true);

}

private void createGUI(){

setDefaultCloseOperation(EXIT_ON_CLOSE);

Container window = getContentPane();

window.setLayout(new FlowLayout() );

panel = new JPanel();

panel.setPreferredSize(new Dimension(300, 200));

panel.setBackground(Color.white);

window.add(panel);

button = new JButton("Press me");

window.add(button);

button.addActionListener(this);

}

public void actionPerformed(ActionEvent event) {

Graphics paper = panel.getGraphics();

paper.drawLine(0, 0, 100, 100);

}

}

Exercício: qual é o erro? Como escrever uma versão do programa acima sem o erro conceitual?

Resposta.