在将Rectangle2D对象放入ArrayList之前,该程序运行良好,只是每当我改变方向时,蛇只会旋转而不是弯曲。现在这条蛇甚至都没有显示出来,并且我的控制台向我显示了错误,如Mad Programmer提供的那样:
Exception in thread "AWT-EventQueue-0" java.lang.IndexOutOfBoundsException:
Index: 0, Size: 0
at java.util.ArrayList.rangeCheck(ArrayList.java:638)
at java.util.ArrayList.get(ArrayList.java:414)
at javaapplication968.JavaApplication968$Display.actionPerformed(JavaApplication968.java:110)
我知道这个问题与ArrayLists有关,但是我该如何解决?
这是我的课:
public class Display extends JPanel implements ActionListener, KeyListener {
Timer t = new Timer(1, this);
double xCoord = 50;
double yCoord = 50;
double xvel = 0;
double yvel = .01;
double ranx, xtemp;
double rany, ytemp;
int eaten = 0;
ArrayList<Rectangle2D> rects = new ArrayList<Rectangle2D>();
ArrayList<Double> xloc = new ArrayList<Double>();
ArrayList<Double> yloc = new ArrayList<Double>();
public Display(int xsize, int ysize) {
t.start();
addKeyListener(this);
setFocusable(true);
setFocusTraversalKeysEnabled(false);
xtemp = xsize;
ranx = (xtemp - 15) * Math.random();
ytemp = ysize;
rany = (ytemp - 15) * Math.random();
formSnake();
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
// Adds snake
g2.setColor(Color.YELLOW);
for (int i = 0; i < rects.size(); i++) {
g2.fill(rects.get(i));
}
// Adds fruit at random location
g2.setColor(Color.BLUE);
g2.fill(new Ellipse2D.Double(ranx, rany, 15, 15));
setBackground(Color.BLACK);
}
@Override
public void actionPerformed(ActionEvent e) {
repaint();
// Replaces each rectangle location with one before it
for (int i = rects.size() - 1; i > 0; i--) {
xloc.set(i, xloc.get(i - 1));
yloc.set(i, yloc.get(i - 1));
}
// Sets new head location
xloc.set(0, xloc.get(0) + xvel);
yloc.set(0, yloc.get(0) + yvel);
getEaten();
}
// Adds initial 3 2DRectangles to snake at start of game
public void formSnake() {
for (int i = 0; i < rects.size(); i++) {
xloc.add(xCoord);
yloc.add(yCoord - 16 * i);
rects.add(rects.size(),
new Rectangle2D.Double(xloc.get(i), yloc.get(i), 15, 15));
}
}
// Adds 1 2DRectangle to the front of the snake every time it eats
public void extend() {
// Vertical
if (xvel == 0) {
if (yvel <= 0) { // Up
xloc.add(xloc.get(xloc.size() - 1));
yloc.add(yloc.get(yloc.size() - 1) - 16);
rects.add(new Rectangle2D.Double(xloc.get(xloc.size() - 1),
yloc.get(yloc.size() - 1), 15, 15));
} else
// Down
xloc.add(xloc.get(xloc.size() - 1));
yloc.add(yloc.get(yloc.size() - 1) + 16);
rects.add(new Rectangle2D.Double(xloc.get(xloc.size() - 1), yloc
.get(yloc.size() - 1), 15, 15));
}
// Horizontal
else if (yvel == 0) {
if (xvel <= 0) { // Left
xloc.add(xloc.get(xloc.size() - 1) - 16);
yloc.add(yloc.get(yloc.size() - 1));
rects.add(new Rectangle2D.Double(xloc.get(xloc.size() - 1),
yloc.get(yloc.size() - 1), 15, 15));
} else
// Right
xloc.add(xloc.get(xloc.size() - 1) + 16);
yloc.add(yloc.get(yloc.size() - 1));
rects.add(new Rectangle2D.Double(xloc.get(xloc.size() - 1), yloc
.get(yloc.size() - 1), 15, 15));
}
}
public void getEaten() {
if (Math.abs(xCoord - ranx) < 15 && Math.abs(yCoord - rany) < 15) {
rany = ytemp * Math.random();
ranx = xtemp * Math.random();
eaten++;
extend();
}
}
//Directions
public void up() {
yvel = -0.5;
xvel = 0;
}
public void down() {
yvel = 0.5;
xvel = 0;
}
public void left() {
xvel = -0.5;
yvel = 0;
}
public void right() {
xvel = 0.5;
yvel = 0;
}
//Just for testing purposes
public void stop() {
xvel = 0;
yvel = 0;
}
//Direction implementation
@Override
public void keyPressed(KeyEvent e) {
int code = e.getKeyCode();
if (code == KeyEvent.VK_UP || code == KeyEvent.VK_NUMPAD8) {
up();
}
if (code == KeyEvent.VK_DOWN || code == KeyEvent.VK_NUMPAD2) {
down();
}
if (code == KeyEvent.VK_RIGHT || code == KeyEvent.VK_NUMPAD6) {
right();
}
if (code == KeyEvent.VK_LEFT || code == KeyEvent.VK_NUMPAD4) {
left();
}
}
@Override
public void keyTyped(KeyEvent e) {
}
@Override
public void keyReleased(KeyEvent e) {
}
}
最佳答案
你似乎正在
Exception in thread "AWT-EventQueue-0" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
at java.util.ArrayList.rangeCheck(ArrayList.java:638)
at java.util.ArrayList.get(ArrayList.java:414)
at javaapplication968.JavaApplication968$Display.actionPerformed(JavaApplication968.java:110)
在
xloc.set(0, xloc.get(0) + xvel);
,因为没有元素,所以xloc
List
更改您的
formSnake
方法以完全按照其说明... // Adds initial 3 2DRectangles to snake at start of game
而不是使用rects.size()
,它在调用时将是0
。 // Adds initial 3 2DRectangles to snake at start of game
public void formSnake() {
for (int i = 0; i < 3; i++) {
xloc.add(xCoord);
yloc.add(yCoord - 16 * i);
rects.add(rects.size(),
new Rectangle2D.Double(xloc.get(i), yloc.get(i), 15, 15));
}
}