这里的想法是创建一个盒子网格。在黑色网格下面是另一个多色盒子网格。当你点击一个方框时，它的面具会消失，显示下方的彩色方框。然后，如果颜色匹配hurray，则单击第二个框，否则则游戏继续。这是GuessingGame.java的代码
import java.applet.Applet;
import java.awt.Button;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class GuessingGame extends Applet{
/**
*
*/
private static final long serialVersionUID = 1L;
private final int START_X = 20;
private final int START_Y = 40;
private final int ROWS = 4;
private final int COLS = 4;
private final int BOX_WIDTH = 20;
private final int BOX_HEIGHT = 20;
//this is used to keep track of boxes that have been matched.
private boolean matchedBoxes[][];
//this is used to keep track of two boxes that have been clicked.
private MaskableBox chosenBoxes[];
private MaskableBox boxes[][];
private Color boxColors[][];
private Button resetButton;
public void init() {
boxes = new MaskableBox[ROWS][COLS];
boxColors = new Color[ROWS][COLS];
resetButton = new Button("Reset Colors");
resetButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
randomizeColors();
buildBoxes();
repaint();
}
});
add(resetButton);
//separate building colors so we can add a button later
//to re-randomize them.
randomizeColors();
buildBoxes();
}
public void paint(Graphics g) {
for (int row =0; row < boxes.length; row ++) {
for (int col = 0; col < boxes[row].length; col++) {
if(boxes[row][col].isClicked()) {
//boxes[row][col].setMaskColor(Color.black);
//boxes[row][col].setMask(!boxes[row][col].isMask());
//boxes[row][col].setClicked(false);
//}
if (!matchedBoxes[row][col]) {
gameLogic(boxes[row][col]);
//boxes[row][col].draw(g);
}
}
}
}
//loop through the boxes and draw them.
for (int row = 0; row < boxes.length; row++) {
for (int col = 0; col < boxes[row].length; col++) {
boxes[row][col].draw(g);
}
}
}
public void gameLogic(MaskableBox box) {
if ((chosenBoxes[0] != null)&&(chosenBoxes[1] != null)) {
chosenBoxes = new MaskableBox[2];
if(chosenBoxes[0].getBackColor() == chosenBoxes[1].getBackColor()) {
for (int i=0; 0 < 2; ++i ) {
for(int row = 0; row < boxes.length; row++) {
for(int col = 0; col < boxes[row].length; col++) {
if( boxes[row][col] == chosenBoxes[i] ) {
System.out.println("boxes [row][col] == chosenBoxes[] at index: " + i );
matchedBoxes[row][col] = true;
break;
}
}
}
}
}else {
chosenBoxes[0].setMask(true);
chosenBoxes[1].setMask(true);
}
}else {
if (chosenBoxes[0] == null) {
chosenBoxes[0] = box;
chosenBoxes[0].setMask(false);
return;
}else{
if (chosenBoxes[1] == null) {
chosenBoxes[1] = box;
chosenBoxes[1].setMask(false);
}
}
}
}
private void removeMouseListeners() {
for(int row = 0; row < boxes.length; row ++) {
for(int col = 0; col < boxes[row].length; col++) {
removeMouseListener(boxes[row][col]);
}
}
}
private void buildBoxes() {
// need to clear any chosen boxes when building new array.
chosenBoxes = new MaskableBox[2];
// create a new matchedBoxes array
matchedBoxes = new boolean [ROWS][COLS];
removeMouseListeners();
for(int row = 0; row < boxes.length; row++) {
for(int col = 0; col < boxes[row].length; col++) {
boxes[row][col] =
new MaskableBox(START_X + col * BOX_WIDTH,
START_Y + row * BOX_HEIGHT,
BOX_WIDTH,
BOX_HEIGHT,
Color.gray,
boxColors[row][col],
true,
true,
this);
addMouseListener(boxes[row][col]);
}
}
}
private void randomizeColors() {
int[] chosenColors = {0,0,0,0,0,0,0,0};
Color[] availableColors = {Color.red, Color.blue, Color.green,
Color.yellow, Color.cyan, Color.magenta, Color.pink, Color.orange };
for(int row = 0; row < boxes.length; row++) {
for (int col = 0; col < boxes[row].length; col++) {
for (;;) {
int rnd = (int) (Math.random() * 8);
if (chosenColors[rnd]< 2) {
chosenColors[rnd]++;
boxColors[row][col] = availableColors[rnd];
break;
}
}
}
}
}
}
这是第二批包含maskablebox的代码
import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
public class MaskableBox extends ClickableBox {
private boolean mask;
private Color maskColor;
Container parent;
public MaskableBox(int x, int y, int width, int height, Color borderColor,
Color backColor, boolean drawBorder, boolean mask, Container parent ) {
super(x, y, width, height, borderColor, backColor, drawBorder, parent);
this.parent = parent;
this.mask = mask;
}
public void draw(Graphics g) {
if(mask=false) {
super.draw(g);
// setOldColor(g.getColor());
// g.setColor(maskColor);
// g.fillRect(getX(),getY(),getWidth(), getHeight());
// if(isDrawBorder()) {
// g.setColor(getBorderColor());
// g.drawRect(getX(),getY(),getWidth(),getHeight());
// }
// g.setColor(getOldColor());
}else {
if(mask=true) {
//super.draw(g);
setOldColor(g.getColor());
g.setColor(maskColor);
g.fillRect(getX(),getY(),getWidth(), getHeight());
if(isDrawBorder()) {
g.setColor(getBorderColor());
g.drawRect(getX(),getY(),getWidth(),getHeight());
}
g.setColor(getOldColor());
}
}
}
public boolean isMask() {
return mask;
}
public void setMask(boolean mask) {
this.mask = mask;
}
public Color getMaskColor() {
return maskColor;
}
public void setMaskColor(Color maskColor) {
this.maskColor = maskColor;
}
}
我现在收到这些错误消息。
Exception in thread "AWT-EventQueue-1" java.lang.NullPointerException
at GuessingGame.gameLogic(GuessingGame.java:74)
at GuessingGame.paint(GuessingGame.java:55)
at java.awt.Container.update(Container.java:1801)
at sun.awt.RepaintArea.updateComponent(RepaintArea.java:239)
at sun.awt.RepaintArea.paint(RepaintArea.java:216)
at sun.awt.windows.WComponentPeer.handleEvent(WComponentPeer.java:306)
at java.awt.Component.dispatchEventImpl(Component.java:4706)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
答案 0 :(得分：0)
因为在第73行你做了：
chosenBoxes = new MaskableBox[2];
即。您创建一个新的MaskableBox数组（新数组中的每个元素将为null）。你要做的下一行是：
chosenBoxes[0].getBackColor() == chosenBoxes[1].getBackColor()
selectedBoxes [0]和selectedBoxes [1]都是null，因为您刚刚在上一行创建了selectedBoxes。删除调用以创建一个新的MaskableBox数组，您将不会得到NullPointerException。
答案 1 :(得分：0)
您在方法NullPointerException中的GuessingGame.java第74行获得gameLogic，该行对应于此行：
if(chosenBoxes[0].getBackColor() == chosenBoxes[1].getBackColor()) {
以及你得到NullPointerException的原因是因为在你之前的行中你做了：
chosenBoxes = new MaskableBox[2];
使用2个引用初始化MaskableBox数组，但实际的MaskableBox 对象也需要实例化 - 这是否有意义？
基本上，经验教训是：创建一个对象数组与创建一个对象数组和初始化数组中的每个元素不同。