当我按下按钮时，我想移动到我设置的范围内

Question

此代码用于移动屏幕截图中显示的图像。

我想要做的是当我点击按钮时，它应该像

一样移动 国际象棋中的骑士。它根本不会移动，显示以下错误。

这是什么问题？我上传了我的代码。

感谢您的帮助并考虑

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;




public class BoardClass extends JFrame{


    private Container contents;

    private JButton[][] squares = new JButton[8][8];
    private Color colorBlack = Color.BLACK;
    private Color colorOrange = Color.ORANGE;

    private int sheeprow=7;
    private int sheepcol=0;

    private int woolfrow1=0;
    private int woolfcol1=1;
    private int woolfrow2=0;
    private int woolfcol2=3;
    private int woolfrow3=0;
    private int woolfcol3=5;
    private int woolfrow4=0;
    private int woolfcol4=7;

    private ImageIcon sheep = new ImageIcon("sheep.PNG");
    private ImageIcon wolf = new ImageIcon("wolf.PNG");

    public BoardClass()
    {
        super("Sheep and wolf game"); 

        contents = getContentPane();
        contents.setLayout(new GridLayout(8, 8));

        ButtonHandler buttonhandler = new ButtonHandler();

        for(int i=0;i<8;i++)
        {
            for(int j=0;j<8;j++)
            {


                squares[i][j] = new JButton();
                if((i+j)%2!=0) // it allows to show black blocks
                {
                    squares[i][j].setBackground(colorBlack);
                }
                else
                {
                    squares[i][j].setBackgroun(colorOrange);
                }
                contents.add(squares[i][j]);
                squares[i][j].addActionListener(buttonhandler);
            }
        }
        squares[sheeprow][sheepcol].setIcon(sheep);
        /*squares[woolfrow1][woolfcol1].setIcon(wolf);
        squares[woolfrow2][woolfcol2].setIcon(wolf);
        squares[woolfrow3][woolfcol3].setIcon(wolf);
        squares[woolfrow4][woolfcol4].setIcon(wolf);*/

        setSize(500,500);
        setResizable(false);
        setLocationRelativeTo(null); //centers window
        setVisible(true);

    }


    private boolean isValidMove(int i, int j)
    {
        int rowDelta = Math.abs(i-sheeprow);
        int colDelta = Math.abs(j-sheepcol);

        if((rowDelta==1) && (colDelta==2))
        {
            return true;
        }
        if((colDelta==1)&&(rowDelta==2))
        {
            return true;
        }
        return false;
    }

    private void processClick(int i, int j)
    {
        if(isValidMove(i,j)==false)
        {
            return;
        }
        squares[sheeprow][sheepcol].setIcon(null);
        squares[i][j].setIcon(sheep);
        sheeprow = i;
        sheepcol = j;
    }

private class ButtonHandler implements ActionListener
{
    public void actionPerformed(ActionEvent e) 
    {
        Object source = e.getSource();

        for(int i=0;i<8;i++)
        {
            for(int j=0;i<8;j++)
            {

                if(source==squares[i][j])-- this part showing some error
                {
                    processClick(i,j);
                    return;
                }
            }
        }

    }
}

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        new BoardClass();
    }
}