java嵌套for（）循环throws ArrayIndexOutOfBoundsException [英] java nested for() loop throws ArrayIndexOutOfBoundsException

问题描述

我正在通过Java书中的JPanel练习。我的任务是使用GridLayout创建一个5x4的网格。

当我循环访问容器来添加面板和按钮时，第一个add（）抛出OOB异常。我做错了什么？

  package mineField; 
 
 import java.awt。*; 
 import javax.swing。*; 
 
 @SuppressWarnings（serial）
 
 public class MineField extends JFrame {
 
 private final int WIDTH = 250; 
 private final int HEIGHT = 120; 
 private final int MAX_ROWS = 5; 
 private final int MAX_COLUMNS = 4; 
 
 public MineField（）{
 
 super（Minefield）; 
 
 setDefaultCloseOperation（JFrame.EXIT_ON_CLOSE）; 
 
容器mineFieldGrid = getContentPane（）; 
 mineFieldGrid.setLayout（new GridLayout（MAX_ROWS，MAX_COLUMNS））; 
 
 //循环通过数组，添加面板，然后向面板添加按钮。 （int i = 0; i  {
 JPanel [] rows = new JPanel [i]; 
 
 mineFieldGrid.add（rows [i]，rows [i] .getName（））; 
 rows [i] .setBackground（Color.blue）; （int j = 0; j< MAX_COLUMNS; j ++）
 
 {
 JButton [] buttons = new JButton [i]; 
 rows [i] .add（buttons [j]，buttons [j] .getName（））; 
} 
} 
 
 mineFieldGrid.setSize（WIDTH，HEIGHT）; 
 mineFieldGrid.setVisible（true）; 
 
} 
 
 public int setRandomBomb（Container con）
 {
 
 int bombID; 
 
 bombID =（int）（Math.random（）* con.getComponentCount（））; 
 return bombID; 
 
 
} 
 / ** 
 * @param args 
 * / 
 public static void main（String [] args）{
 
 // int randomBomb; 
 // JButton bombLocation; 
 
 MineField minePanel = new MineField（）; 
 // minePanel [randomBomb] = minePanel.setRandomBomb（minePanel）; 
 
} 
  

}

$ b $我确定我过度工程了一个简单的嵌套for循环。由于我是Java的新手，请善待。我确定我会有一天会回来。

解决方案

JPanel [] rows = new JPanel [i];

i 在第一次迭代中为0，你想要什么这样做：

JPanel [] rows = new JPanel [MAX_ROWS];

另外，我想你想把它完全从的循环之外，因为你似乎正在使用它的元素，这将是未初始化的。

这也是错误的：

JButton [] buttons = new JButton [ i];

我可以为0，当 j例如，是2，在这种情况下，没有像按钮[j] 这样的东西。使它们全部 MAX _ * ，我想你想把它们从循环中移除，因为我在每次迭代中都没有看到重新创建它们。此外，您还需要实例化各个数组元素。

I'm working through a JPanel exercise in a Java book. I'm tasked with creating a 5x4 grid using GridLayout.

When I loop through the container to add panels and buttons, the first add() throws the OOB exception. What am I doing wrong?

package mineField;

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

@SuppressWarnings("serial")

public class MineField extends JFrame {

private final int WIDTH = 250;
private final int HEIGHT = 120;
private final int MAX_ROWS = 5; 
private final int MAX_COLUMNS = 4;

public MineField() {

    super("Minefield");

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    Container mineFieldGrid = getContentPane();
    mineFieldGrid.setLayout(new GridLayout(MAX_ROWS, MAX_COLUMNS));

    // loop through arrays, add panels, then add buttons to panels.
    for (int i = 0; i < MAX_ROWS; i++) {
        JPanel[] rows = new JPanel[i];

        mineFieldGrid.add(rows[i], rows[i].getName());
        rows[i].setBackground(Color.blue);

        for (int j = 0; j < MAX_COLUMNS; j++) {
            JButton[] buttons = new JButton[i];             
            rows[i].add(buttons[j], buttons[j].getName());
        }
    }

    mineFieldGrid.setSize(WIDTH, HEIGHT);
    mineFieldGrid.setVisible(true);

}

public int setRandomBomb(Container con)
{

    int bombID;

    bombID = (int) (Math.random() * con.getComponentCount());
    return bombID;


}
/**
 * @param args
 */
public static void main(String[] args) {

    //int randomBomb;
    //JButton bombLocation;

    MineField minePanel = new MineField();
    //minePanel[randomBomb] = minePanel.setRandomBomb(minePanel);

}

}

I'm sure I'm over-engineering a simple nested for loop. Since I'm new to Java, please be kind. I'm sure I'll return the favor some day.

解决方案

JPanel[] rows = new JPanel[i];

i is 0 in the first iteration, which isn't what you want. Make that:

JPanel[] rows = new JPanel[MAX_ROWS];

Also, I think you want to take that completely outside the for loop, since you seem to be using its elements, which would be uninitialised...

This is also wrong:

JButton[] buttons = new JButton[i];

i can be 0 when j is 2 for example, in which case there's no such thing as a buttons[j]. Make them all MAX_* and I think you want to take them out of the loop, since I don't see the point in recreating them at every iteration. Also, you need to instantiate the individual array elements as well.

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