メソッドCaballoで再帰メソッドを作成しようとしているので、ナイトを移動できますが、NullPointerExceptionが発生し、再帰が機能しません。何か提案をいただけますか? チェスに似たゲームを作ろうとしています。
package ratsuk;
import javax.swing.JFrame;
import javax.swing.JButton;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JPanel;
import java.util.Random;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JLabel;
/**
*
* @author Melvin
*/
public class Tablero {
private JButton[][] mesa;
private Random rad;
private Icon image;
private JPanel panel;
public Tablero() {
mesa = new JButton[8][8];
panel = new JPanel(new GridLayout(8, 8, 0, 0));
image = new ImageIcon(getClass().getResource("redKnight.gif"));
}
public void cuadriculado(JFrame ventana) {
for (int i = 0; i < mesa.length; i++) {
for (int j = 0; j < mesa[0].length; j++) {
mesa[i][j] = new JButton();
mesa[i][j].setPreferredSize(new Dimension(40, 40));
panel.add(mesa[i][j]);
}
}
for (int r = 0; r < mesa.length; r++) {
for (int t = 0; t < mesa[0].length; t++) {
if (r % 2 == 0 || r == 0) {
if (t % 2 == 0 || t == 0) {
mesa[r][t].setBackground(Color.BLACK);
} else {
mesa[r][t].setBackground(Color.WHITE);
}
} else {
if (t % 2 == 0 || t == 0) {
mesa[r][t].setBackground(Color.WHITE);
} else {
mesa[r][t].setBackground(Color.BLACK);
}
}
}
}
ventana.setContentPane(panel);
ventana.setSize(500, 500);
ventana.setVisible(true);
}
public void Caballo(final int i, final int j) {
final Tablero cab =new Tablero();
mesa[i][j].setIcon(image);
mesa[i][j].addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
//Execute when button is pressed
mesa[i][j].setBackground(Color.RED);
}
});
mesa[i+2][j-1].addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent d) {
//Execute when button is pressed
if (cab.tienebotton(i+2, j-1)==true){
mesa[i+2][j-1].setIcon(image);
mesa[i][j].setIcon(null);
cab.Caballo(i+2,j-1);
}
}
});
panel.repaint();
}
public boolean tienebotton(int k, int w) {
for(int i = 0; i < mesa.length; i++) {
for(int j = 0; j < mesa[i].length; j++) {
if(mesa[k][w] == mesa[i][j]) return true;
}
}
return false;
}
}
nullpointerexceptions の行は次のとおりです。
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at ratsuk.Tablero.Caballo(Tablero.java:76)
at ratsuk.Tablero$2.actionPerformed(Tablero.java:93)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.awt.EventQueue$3.run(EventQueue.java:686)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:702)
at java.awt.EventQueue$4.run(EventQueue.java:700)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
これはコードの残りの部分です：
package ratsuk;
import java.util.Random;
import javax.swing.JFrame;
/**import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
*/
public class Ratsuk extends JFrame {
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
// TODO code application logic here
Random rad;
JFrame ventana;
ventana= new JFrame ("Juego de Ratsuk");
rad= new Random();
int azar= rad.nextInt(8);
int azar2 = rad.nextInt(8);
ventana.setVisible(true);
ventana.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Tablero newtablero= new Tablero();
newtablero.cuadriculado( ventana);
newtablero.Caballo(azar,azar2);
}
}