我想先说这是一个任务。我不想让勺子喂给我,但我想知道是什么导致了我的问题。Java:填充网格上的矩形
我目前正在执行康威生命游戏。单击单元格应改变颜色,以表示该单元格正在切换到活动状态。如果再次点击,它应该返回到默认颜色。
当我在窗口中单击任意位置,该程序在罚球线上56空指针异常一直停留在这最后一天左右,所以任何帮助表示赞赏。谢谢!
继承人的代码:
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class VisibleGrid extends JPanel implements MouseListener, KeyListener{
CellGrid cellGrid;
Graphics rect;
public VisibleGrid(){
addMouseListener(this);
cellGrid = new CellGrid();
}
//Draw the grid of cells, 7px wide, 75 times to create 75x75 grid
public void paint(Graphics g){
for(int i=0; i<525;i=i+7){
for(int j = 0; j<525; j=j+7){
g.drawRect(i ,j,7,7);
}
}
}
//auxillary method called to fill in rectangles
public void paint(Graphics g, int x, int y){
g.fillRect(x, y, 7, 7);
repaint();
}
//main method, adds this JPanel to a JFrame and sets up the GUI
public static void main(String[] args){
JFrame j = new JFrame("Conway's Game of Life");
j.setLayout(new BorderLayout());
j.add(new VisibleGrid(), BorderLayout.CENTER);
JTextArea info = new JTextArea("Press S to Start, E to End");
info.setEditable(false);
j.add(info, BorderLayout.SOUTH);
j.setSize(530,565);
j.setVisible(true);
}
//these methods are to satisfy the compiler/interface
//Begin Mouse Events
public void mouseExited(MouseEvent e){}
public void mouseEntered(MouseEvent e){}
public void mouseReleased(MouseEvent e){}
public void mousePressed(MouseEvent e){}
public void mouseClicked(MouseEvent e){
//fill the selected rectangle
rect.fillRect(e.getX(), e.getY(), 7,7);
repaint();
//set the corresponding cell in the grid to alive
int row = e.getY() /7;
int column = e.getX() /7;
cellGrid.getCell(row, column).setAlive(true);
}
//End Mouse Events
//These methods are to satisfy the compiler/interface
//Begin KeyEvents
public void keyReleased(KeyEvent e){}
public void keyPressed(KeyEvent e){}
public void keyTyped(KeyEvent e){}
}
哪条线是线56?当我复制/粘贴代码时,它是int column = e.getX()/ 7;这看起来不正确 – 2012-04-29 05:26:34
我敢打赌线56 _rect.fillRect(e.getX(),e.getY(),7,7); _ – 2012-04-29 05:29:18
作为@guido说,确保对象的图形,'rect'在访问之前被初始化或有一个有效的参考。 – Rupak 2012-04-29 08:34:42