我想保存此按钮，并在下次有人点击另一个按钮时更改它的图标，但它在我说的button2.setIcon（icon）行上给了我nullpointer异常; 。如何保存此按钮并在下次更改它的图标？或者如何在构造函数中访问按钮数组？有可能吗？
package tictactoe;
// import necessary classes and interfaces
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.LinkedHashSet;
import java.util.Random;
import java.util.Set;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
public class TicTacToeGame extends JFrame {
/**
*
*/
boolean lock=false;
//int for_the_first_time=1;
int temp1;
int temp2;
int selected=0;
Icon ic;
int row ;
int col ;
Icon[] array = new Icon[12];
Icon[] arrayc = new Icon[12];
int[] random_array = new int[12];
int[] arrayint = new int[12];
int[] arrayintc = new int[12];
private static final long serialVersionUID = 1L;
private final static int ROWS = 3;
private final static int COLUMNS = 4;
private JButton button[];
private JPanel buttonsPanel;
private JButton exitButton;
Icon icon = new ImageIcon(getClass().getResource("scene.jpg"));
public TicTacToeGame()
{
// set frame's title
this.setTitle( "Remember Me" );
buttonsPanel = new JPanel();
// set panel's layout manager
buttonsPanel.setLayout( new GridLayout( ROWS , COLUMNS , 1 , 1 ) );
// create a JButton object named exitButton
exitButton = new JButton("Exit");
//register an ActionListener for exitButton
exitButton.addActionListener(
new ActionListener()
{
public void actionPerformed( ActionEvent ae )
{
// do a normal exit
System.exit( 0 );
}
}
);
// add exitButton to frame
this.add( exitButton , BorderLayout.SOUTH );
// create an array of JButtons
button = new JButton[ ROWS * COLUMNS ];
// initialize each button and add it to buttonsPanel
for ( int i = 0 ; i < 12 ; i++ ) {
array[i]= new ImageIcon(getClass().getResource(i+".jpg"));
arrayint[i]=i;
}
//create not repeating random numbers:
Random rng = new Random(); // Ideally just create one instance globally
// Note: use LinkedHashSet to maintain insertion order
Set<Integer> generated = new LinkedHashSet<Integer>();
while (generated.size() < 12)
{
Integer next = rng.nextInt(12);
// As we're adding to a set, this will automatically do a containment check
generated.add(next);
}
String str = generated.toString();
str = str.replaceAll("\\s", "");
str = str.replace("[", "");
str = str.replace("]", "");
String[] str2= str.split(",");
for (int i=0;i<12;i++){
random_array[i]= Integer.parseInt(str2[i]);
}
for (int i=0;i<12;i++){
arrayc[i]=array[random_array[i]];
arrayintc[i]=arrayint[random_array[i]];
}
for ( int i = 0 ; i < ROWS * COLUMNS ; i++ ) {
button[ i ] = new JButton();
button[ i ].setFocusPainted( false );
button[ i ].setActionCommand( Integer.toString( i ) );
button[ i ].setFont( new Font( "Tahoma" , Font.BOLD , 15 ) );
button[ i ].setPreferredSize( new Dimension( 100 , 100 ) );
button[ i ].setToolTipText( "Click to make your move" );
button[ i ].addActionListener( new ButtonClickHandler() );
button[ i ].setIcon(arrayc[i]);
buttonsPanel.add( button[ i ] );
}
// add buttonsPanel to frame
this.add(buttonsPanel, BorderLayout.NORTH);
// set some of JFrame's propeties
this.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
// don't allow user to resize the Jframe
this.setResizable( false );
// resize frame to a suitable size
this.pack();
// don't allow user to resize the game window
this.setVisible( true );
try{
Thread.sleep(2000);
for ( int i = 0 ; i < ROWS * COLUMNS ; i++ ) {
button[ i ].setIcon(icon);
}
}catch(InterruptedException e){
}
// resetGame();
} // end of class constructor
private class ButtonClickHandler implements ActionListener
{
public void actionPerformed( ActionEvent event )
{
int count=0;
JButton button = (JButton) event.getSource();
Set_Rows_Columns(button);
check_if_possible_to_show(count, button);
}
JButton button2;
int for_the_first_time=1;
boolean stable=false;
private void check_if_possible_to_show(int count, JButton button) {
if (selected==1){
button2.setIcon(icon);
is_going_to_be_stable(temp1,arrayintc[count],count,button);
}
else{
temp1=arrayintc[count];
button2=button;
selected=1;
button.setIcon(arrayc[count]);
} }
private void is_going_to_be_stable(int temp1, int temp2,int count, JButton button) {
int temp1v;
int temp2v;
boolean bool=false;
if (temp1==0){
if (temp2==6){
bool= true;
}
}
if (temp1==1){
if (temp2==7){
bool= true;
}
}
if (temp1==2){
if (temp2==8){
bool= true;
}
}
if (temp1==3){
if (temp2==9){
bool= true;
}
}
if (temp1==4){
if (temp2==10){
bool= true;
}
}
if (temp1==5){
if (temp2==11){
bool= true;
}
}
if (bool==true){
button.setIcon(arrayc[count]);
button2.setIcon(arrayc[1]);
}
else{
button2.setIcon(icon);
button.setIcon(arrayc[count]);
}
}
public void Set_Rows_Columns(JButton button) {
if(button.getActionCommand().equals("0")){
row=0; col=0;
}
if(button.getActionCommand().equals("1")){
row=0; col=1;
}
if (button.getActionCommand().equals("2")){
row=0; col=2;
}
if (button.getActionCommand().equals("3")){
row=0; col=3;
}
if (button.getActionCommand().equals("4")){
row=1; col=0;
}
if (button.getActionCommand().equals("5")){
row=1; col=1;
}
if (button.getActionCommand().equals("6")){
row=1; col=2;
}
if (button.getActionCommand().equals("7")){
row=1; col=3;
}
if (button.getActionCommand().equals("8")){
row=2; col=0;
}
if (button.getActionCommand().equals("9")){
row=2; col=1;
}
if (button.getActionCommand().equals("10")){
row=2; col=2;
}
if (button.getActionCommand().equals("11")){
row=2; col=3;
}
}
}
} // end of class TicTacToeGame
答案 0 :(得分：0)
首先要说的是：您可以缩短代码。 而不是is_going_to_be_stable方法 你可以用这个：
if (
(temp1 == 0 && temp2 == 6) ||
(temp1 == 1 && temp2 == 7) ||
(temp1 == 2 && temp2 == 8) ||
(temp1 == 3 && temp2 == 9) ||
(temp1 == 4 && temp2 == 10) ||
(temp1 == 5 && temp2 == 11)
){
button.setIcon(arrayc[count]);
button2.setIcon(arrayc[1]);
} else{
button2.setIcon(icon);
button.setIcon(arrayc[count]);
}
而不是Set_Rows_Columns方法，您可以使用此
switch(button.getActionCommand()){
case "0":
row=0; col=0;
break;
//and so on
}
你不应该说
private JButton button[];
你应该说
private JButton[] button;
我不知道问题是否已解决。