爲什麼我的數組對象在我的8x8網格內移動出界？

Question

我有一個對象（BigCrawler）超出界限，並且每次在我的8x8網格中點擊0和7時，在北和南端但不是東西兩側都會出現空指針異常。我的NPE是

Exception in thread "AWT-EventQueue-0" java.lang.ArrayIndexOutOfBoundsException: 8 
     at GridPanel.containsToken(GridPanel.java:78) 
     at BigCrawler.canMove(BigCrawler.java:63) 
     at BigCrawler.move(BigCrawler.java:79) 

我很積極，這是我的邏輯內的東西。我有3個其他物體，它們實例化，2個向東和向西移動，而另一個物體每次按下移動按鈕時向南和向南移動。他們每個人都工作得很好，但由於某種原因，只要我的BigCrawler對象觸及南端或北端，它就不會退後，而是以其他方式繼續提供NPE。 BTW第79行是發佈的第三條if語句。我可以發佈任何需要的代碼，但我相信它在發佈的區域內。

我BigCrawler.java

//************************************************************************ 
// BigCrawler.java 
// 
// 
//************************************************************************ 


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

public class BigCrawler extends Crawler 
{ 

//*********************************************************************************** 
// Instance variables 
//*********************************************************************************** 

private int legs; 

//*********************************************************************************** 
// Constructors 
//*********************************************************************************** 

public BigCrawler(String name, ImageIcon image, String direction, int legs) 
{  super(name, image, direction, 1); 

    if (!(direction.equals("NorthEast") || direction.equals("SouthWest"))) 
     direction = "NorthEast"; 


    this.legs = legs; 
} 


//*********************************************************************************** 
// Accessors 
//*********************************************************************************** 

public int getLegs() 
{ return legs; 
} 

//*********************************************************************************** 
// Mutators 
//*********************************************************************************** 

public void setLegs(int legs) 
{ this.legs = legs; 
} 


//*********************************************************************************** 
// Additional Methods 
//*********************************************************************************** 

public String toString() 
{ 
    return super.toString() + "and has " + legs + " creepy crawly legs."; 
} 

public boolean canMove(GridPanel bugGrid, int newRow, int newColumn) 
    { if (bugGrid.containsToken(newRow, newColumn)) 
      return false; 
     else 
      return true; 
    } 

public void move(GridPanel bugGrid) 
    { 
    if (direction == "NorthEast" && column == bugGrid.getBoardColumns()-1) 
     direction = "SouthWest"; 
    else if (direction == "SouthWest" && column == 0) 
     direction = "NorthEast"; 

    if (direction == "SouthWest") 
    {  column--; 
      row++; 
      if (canMove(bugGrid, row, column)) 
      { bugGrid.addImage(null, row-1, column+1); 
       bugGrid.addImage(image, row, column); 
      } 
      else 
      { column++; 
      row--;} 
    } 

    else 
    {  column++; 
      row--; 
      if (canMove(bugGrid, row, column)) 
      { bugGrid.addImage(null, row+1, column-1); 
       bugGrid.addImage(image, row, column); 
      } 
      else 
      { column--; 
       row++;} 
    } 
    } 


} 

和我的GridPanel

 //******************************************************************** 
    // GridPanel.java  Java Foundations 
    // 
    // A grid panel to represent a game board of buttons (8x8 default). 
    // The buttons use an ImageIcon to display the playing "pieces" 
    //******************************************************************** 

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

    public class GridPanel extends JPanel 
    { 
     //----------------------------------------------------------------- 
     // Sets up this panel with some buttons to show how grid 
     // layout affects their position, shape, and size. 
     //----------------------------------------------------------------- 

     //----------------------------------------------------------------- 
     // The only instance data item is an 8x8 array of buttons 
     //----------------------------------------------------------------- 
     private int rows, columns; 
     private JButton[][] buttonArray; 

     //------------------------------------------------------------------------------------------- 
     // The constructor for the panel. This sets up the array using a GridLayout GUI component 
     // The text on each button is blank and no ImageIcons are loaded. 
     //------------------------------------------------------------------------------------------- 
     public GridPanel(int rows, int columns) 
     { 
      if (rows > 0 && columns > 0) 
      { this.rows = rows; 
      this. columns = columns; 
      buttonArray = new JButton[rows][columns]; 
      setLayout(new GridLayout(rows,columns)); } 
      else 
      { rows = 8; 
      columns = 8; 
      buttonArray = new JButton[8][8]; 
      setLayout(new GridLayout(8,8));    } 

      setBackground(Color.green); 


      for (int i = 0; i < rows; i++) 
      for (int j = 0; j < columns; j++) 
       buttonArray[i][j] = new JButton(" "); 

      for (int i = 0; i < rows; i++) 
      for (int j = 0; j < columns; j++) 
       add(buttonArray[i][j]); 

     } 

     //------------------------------------------------------------------------------------------- 
     // Accessors to return board size 
     //------------------------------------------------------------------------------------------- 
     public int getBoardRows() 
     { return rows; } 


     public int getBoardColumns() 
     { return columns; } 


    //------------------------------------------------------------------------------------------- 
     // A method to add an ImageIcon image to a specific position on the board 
     //------------------------------------------------------------------------------------------- 
     public void addImage(ImageIcon image, int row, int col) 
     { 
      if (row < rows && row >= 0 && col < columns && col >=0) 
       buttonArray[row][col].setIcon(image); 
     } 
     //------------------------------------------------------------------------------------------- 
     // A method to check to see if an image (playing piece) contains exists on the board 
     //------------------------------------------------------------------------------------------- 
     public boolean containsToken(int row, int col) 
      { 
       if (buttonArray[row][col].getIcon() != null) return true; else return false; 

     } 

    } 

和我的司機設置事事休

 //******************************************************************** 
     // LayoutDemo.java  Java Foundations 
     // 
     // Driver for the bugs game 
     //******************************************************************** 

     import javax.swing.*; 

     public class BugsDriver 
     { 
      //----------------------------------------------------------------- 
      // Sets up a frame containing a tabbed pane. The panel on each 
      // tab demonstrates a different layout manager. 
      //----------------------------------------------------------------- 
      public static void main(String[] args) 
      { 
       JFrame frame = new JFrame("Move the Bugs"); 
       frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

       BorderPanel bugsGame = new BorderPanel(); 


       frame.getContentPane().add(bugsGame); 

       frame.pack(); 
       frame.setVisible(true); 
      } 
     } 

Answer 1

== - 返回true，如果兩個Object是指到相同的引用 .equals - 如果String對象表示返回true與這個對象有相同的字符序列。

更改此部分：

if (direction == "NorthEast" && column == bugGrid.getBoardColumns()-1) 
     direction = "SouthWest"; 
    else if (direction == "SouthWest" && column == 0) 
     direction = "NorthEast"; 

    if (direction == "SouthWest") 

Answer 2

想通了自己。它根本不需要處理==或.equals。雖然我會在下次採納這個建議。問題是我不得不更新對象選擇它的方向的參數。