print() 方法未打印正确的 ArrayList 内容

Question

我的代码像这样将十进制转换为二进制：

for(int i = 0; i < combinations; i++)
    {
        int binary[] = new int[numV];
        if(i == 0)
        {
            for(int j = 0; j < numV; j++)
            {
                binary[j] = 0;
            }
        }
        else if(i > 0)
        {
            binary = values.get(i-1);
            for(int a = numV-1; a >= 0; a--)
            {
                System.out.println(a);
                if(binary[a]==0)
                {
                    binary[a]++;
                    break;
                }
                else
                    binary[a]=0;
            }
        }
        values.add(binary);
    }

如您所见，ArrayList<int[]> 类型的 values 对象存储 i 的二进制值（来自实例化整数数组 binary，该数组由 i 的每个循环创建）。然而，在为每个i 打印二进制数的所有整数数组表示后，从列表中立即给出以下输出：

0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000

我的print() 部分代码工作正常。 ArrayList 中的内容不正确，我不知道为什么。有人可以指出我的愚蠢错误吗？谢谢。

编辑：当我打印时，它只打印 LAST arraylist 的整数数组（当我在 for 循环之后打印时）。但是，当我在 for 循环中打印刚刚添加到数组列表中的内容时，它的内容是正确的。

完整代码：

    import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class KMap extends JFrame
{
    private ArrayList<String> variableNameList = new ArrayList<String>();
    private String [] characters = {"A","B","C","D","E","F","G","H","I","J"};
private ArrayList<int[]> values = new ArrayList<int[]>();
public KMap() 
{
    setTitle("Karnaugh Map for COMP 228");
    setLayout(new BorderLayout());
    createTopPane();
    updateVarialbes(4);
    pack();
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);
    setLocationRelativeTo(null);
}
public void createTopPane()
{
    JPanel topPanel = new JPanel();
    topPanel.setLayout(new GridLayout(1,10));
    JLabel numVariablesString = new JLabel();
    numVariablesString.setText("# Variables => ");
    topPanel.add(numVariablesString);
    JButton[] variableButton = new JButton[9];
    for(int i = 0; i < variableButton.length; i++)
    {
        int numV = i+2;
        variableButton[i] = new JButton();
        variableButton[i].setText(Integer.toString(numV));
        variableButton[i].addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e) 
            {
                removeLeftPane();
                removeRightPane();
                updateVarialbes(numV);
            }
        });

        topPanel.add(variableButton[i]);
    }
    add(topPanel, BorderLayout.NORTH);
}
public void updateVarialbes(int numV)
{
    int combinations = (int) Math.pow(2,numV) + 1;
    System.out.println(combinations);
    System.out.println("New variables: " + numV);
    values.clear();
    variableNameList.clear();
    for(int i = 0; i < numV; i++)
        variableNameList.add(characters[i]);
    System.out.println();
    for(int i = 0; i < combinations; i++)
    {
        int binary[] = new int[numV];
        if(i == 0)
        {
            for(int j = 0; j < numV; j++)
            {
                binary[j] = 0;
            }
        }
        else if(i > 0)
        {
            binary = values.get(i-1);
            for(int a = numV-1; a >= 0; a--)
            {
                System.out.println(a);
                if(binary[a]==0)
                {
                    binary[a]++;
                    break;
                }
                else
                    binary[a]=0;
            }
        }
        values.add(binary);
    }

    for(int i = 0; i < values.size(); i++)
    {
        for(int j = 0; j < values.get(i).length; j++)
            System.out.print(values.get(i)[j]);
        System.out.println();
    }



    createLeftPane(numV);
    createRightPane(numV);
}
public void createLeftPane(int numV)//numV = number of variables to display
{
    JPanel leftPanel = new JPanel();
    leftPanel.setLayout(new GridLayout(2,2));



    JLabel variableLabel[] = new JLabel[numV];
    JPanel topLeftInnerPanel = new JPanel();
    topLeftInnerPanel.setLayout(new GridLayout(1,numV));
    for(int i = 0; i < numV; i++)
    {
        variableLabel[i] = new JLabel();

        variableLabel[i].setText(variableNameList.get(i));
        topLeftInnerPanel.add(variableLabel[i]);
    }
    leftPanel.add(topLeftInnerPanel);



    JPanel topRightInnerPanel = new JPanel();
    JLabel functionLabel = new JLabel();
    String s = "F(";
    for(int i = 0; i < numV; i++)
    {
        s+=characters[i];
        if(i!=numV-1)
            s+=",";
    }
    s+=(")");
    System.out.println(s);
    functionLabel.setText(s);
    topRightInnerPanel.add(functionLabel);
    leftPanel.add(topRightInnerPanel);




    JPanel innerLeftPanel = new JPanel();
    innerLeftPanel.setLayout(new GridLayout(values.size(), 1));
    JPanel[] innerLeftValuesPanel = new JPanel[values.size()];
    for(int i = 0; i < values.size(); i++)
    {
        innerLeftValuesPanel[i] = new JPanel();
        innerLeftValuesPanel[i].setLayout(new GridLayout(1, numV));
        for(int j = 0; j < values.get(i).length; j++)
        {
            JLabel l = new JLabel();
            l.setText(Integer.toString(values.get(i)[j]));
            innerLeftValuesPanel[i].add(l);
        }
    }

    for(int i = 0; i < (2^numV); i++)
        innerLeftPanel.add(innerLeftValuesPanel[i]);
    leftPanel.add(innerLeftPanel);


    JPanel innerRightPanel = new JPanel();
    innerRightPanel.setLayout(new GridLayout(2^numV, 1));

    add(leftPanel);

}
public void removeLeftPane()
{

}
public void createRightPane(int numV)
{

}
public void removeRightPane()
{

}

}

Answer 1

损害是由看似无害的声明造成的

binary = values.get(i-1);

访问在上一次迭代中添加的List<int[]> 末尾的int[]。现在binary 引用该整数数组，以下操作修改上一次迭代中存储的数组。最后，

values.add(binary);

将对该数组的引用作为另一个元素添加到列表中，无论它有多少元素，它都引用同一个 int[] 以及所有存储的引用。

解决方法很简单：不要将引用复制到数组对象，而是复制数组本身。

binary = Arrays.copyOf(values.get(i-1), numV );