实例042 反转数组中元素的顺序

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实例042 反转数组中元素的顺序

实例说明

反转数组就是以相反的顺序把原有数组的内容重新排序。本实例在GUI窗体中演示反转数组中元素的顺序。运行本实例,首先在界面的文本框内输入数组元素,每个元素使用空格分隔,然后单击界面上的“反转数组元素”按钮,程序将对数组进行反转运算,并把运算过程中对数组的改变显示在窗体中。实例的运行效果如图516所示。

反转和倒序排序的区别

脚下留神:“反转”并不等于“倒序排序”。

  • “反转”只是将数组元素的顺序进行颠倒,并不对其执行排序操作;
  • 而“倒序排序”则是对数组中的元素进行从大到小的排序。

实现过程

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private void reverseArray(int[] array)
{
    int temp;
    int i_thFromLast;
    for (int i = 0; i < array.length / 2; i++)
    {
        // 计算倒数第i个元素的索引
        i_thFromLast = array.length - 1 - i;
        // 将第i个元素和倒数第i个元素交换
        temp = array[i];
        array[i] = array[i_thFromLast];
        array[i_thFromLast] = temp;
        printSwapStep(array, i_thFromLast, i);
    }
}

技术要点

本实例的核心技术是使用了数组反转算法。反转算法的基本思想比较简单,也很好理解,思路就是:

  • 把数组最后一个元素与第一个元素替换,
  • 倒数第二个元素与第二个元素替换,
  • 依此类推,直到把所有数组元素反转替换。

反转数组元素是对数组两边的元素进行替换,所以只需要循环数组长度的半数。例如,对长度为6的一维数组进行反转,只需要循环6/2,即3次,具体的反转过程如图517所示

完整代码

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package com.lan;

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.KeyStroke;
import javax.swing.UIManager;
import javax.swing.border.EmptyBorder;
import javax.swing.border.TitledBorder;

public class ReverseArray extends JFrame
{
    private final class ReverseButtonListener implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            String[] arrayStrs = textAreaInput.getText().split(",");
            int[] array = new int[arrayStrs.length];
            for (int i = 0; i < array.length; i++)
            {
                array[i] = Integer.parseInt(arrayStrs[i]);
            }
            reverseArray(array);
        }
        private void reverseArray(int[] array)
        {
            int temp;
            int i_thFromLast;
            for (int i = 0; i < array.length / 2; i++)
            {
                // 计算倒数第i个元素的索引
                i_thFromLast = array.length - 1 - i;
                // 将第i个元素和倒数第i个元素交换
                temp = array[i];
                array[i] = array[i_thFromLast];
                array[i_thFromLast] = temp;
                printSwapStep(array, i_thFromLast, i);
            }
        }
        private void printSwapStep(int[] array, int i_thFromLast, int i)
        {
            for (int j = 0; j < array.length; j++)
            {
                if (j == i)
                {
                    textAreaShow.append("[");
                }
                textAreaShow.append(String.valueOf(array[j]));
                if (j == i_thFromLast)
                {
                    textAreaShow.append("]");
                }
                if (j < array.length - 1)
                {
                    textAreaShow.append(",");
                }
            }
            textAreaShow.append("\n");
        }
    }

    private static final long serialVersionUID = 5911081012919816847L;
    private JPanel contentPane;
    private JTextArea textAreaShow = new JTextArea();
    private JTextArea textAreaInput = new JTextArea();
    private final JMenuBar menuBar = new JMenuBar();
    private final JMenu menu = new JMenu("菜单");
    private final JMenuItem menuItem = new JMenuItem("退出");

    /**
     * Launch the application.
     */
    public static void main(String[] args)
    {
        EventQueue.invokeLater(new Runnable() {
            public void run()
            {
                try
                {
                    ReverseArray frame = new ReverseArray();
                    frame.setVisible(true);
                } catch (Exception e)
                {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public ReverseArray() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        menuItem.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e)
            {
                dispose();
            }
        });
        // 为菜单设置alt+f快捷键(助记符)
        menu.setMnemonic('F');
        GridBagConstraints gbc_menuBar = new GridBagConstraints();
        gbc_menuBar.anchor = GridBagConstraints.EAST;
        gbc_menuBar.gridx = 0;
        gbc_menuBar.gridy = 0;

        contentPane.add(menuBar, gbc_menuBar);
        menuBar.add(menu);
        menu.add(menuItem);
        // 为菜单项设置快捷键
        KeyStroke Ctrl_Shift_W = KeyStroke.getKeyStroke(KeyEvent.VK_W, KeyEvent.CTRL_DOWN_MASK + KeyEvent.SHIFT_DOWN_MASK);
        menuItem.setAccelerator(Ctrl_Shift_W);

        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        GridBagLayout gbl_contentPane = new GridBagLayout();
        gbl_contentPane.columnWidths = new int[]{0, 0};
        gbl_contentPane.rowHeights = new int[]{0, 0, 0, 0, 0};
        gbl_contentPane.columnWeights = new double[]{1.0, Double.MIN_VALUE};
        gbl_contentPane.rowWeights = new double[]{0.0, 0.0, 0.0, 1.0, Double.MIN_VALUE};
        contentPane.setLayout(gbl_contentPane);

        JPanel panel = new JPanel();
        panel.setBorder(new TitledBorder(UIManager.getBorder("TitledBorder.border"),
                "\u8F93\u5165\u6570\u7EC4\u5143\u7D20,\u4EE5\u82F1\u6587\u9017\u53F7\u5206\u9694,\u5982:1,2,3,4,5", TitledBorder.LEFT,
                TitledBorder.TOP, null, new Color(0, 0, 0)));
        GridBagConstraints gbc_panel = new GridBagConstraints();
        gbc_panel.fill = GridBagConstraints.BOTH;
        gbc_panel.insets = new Insets(0, 0, 5, 0);
        gbc_panel.gridx = 0;
        gbc_panel.gridy = 1;
        contentPane.add(panel, gbc_panel);
        GridBagLayout gbl_panel = new GridBagLayout();
        gbl_panel.columnWidths = new int[]{0, 0};
        gbl_panel.rowHeights = new int[]{0, 0};
        gbl_panel.columnWeights = new double[]{1.0, Double.MIN_VALUE};
        gbl_panel.rowWeights = new double[]{0.0, Double.MIN_VALUE};
        panel.setLayout(gbl_panel);

        GridBagConstraints gbc_textAreaInput = new GridBagConstraints();
        gbc_textAreaInput.fill = GridBagConstraints.BOTH;
        gbc_textAreaInput.gridx = 0;
        gbc_textAreaInput.gridy = 0;
        panel.add(textAreaInput, gbc_textAreaInput);

        JButton buttonReverse = new JButton("反转数组");
        // 为按钮绑定组合快捷键
        buttonReverse.registerKeyboardAction(new ReverseButtonListener(), KeyStroke.getKeyStroke(KeyEvent.VK_B, KeyEvent.CTRL_DOWN_MASK),
                JComponent.WHEN_IN_FOCUSED_WINDOW);
        buttonReverse.addActionListener(new ReverseButtonListener());
        GridBagConstraints gbc_buttonReverse = new GridBagConstraints();
        gbc_buttonReverse.insets = new Insets(0, 0, 5, 0);
        gbc_buttonReverse.gridx = 0;
        gbc_buttonReverse.gridy = 2;
        contentPane.add(buttonReverse, gbc_buttonReverse);

        GridBagConstraints gbc_textAreaShow = new GridBagConstraints();
        gbc_textAreaShow.insets = new Insets(0, 0, 5, 0);
        gbc_textAreaShow.fill = GridBagConstraints.BOTH;
        gbc_textAreaShow.gridx = 0;
        gbc_textAreaShow.gridy = 3;
        contentPane.add(textAreaShow, gbc_textAreaShow);
    }
}

Swing设置组合快捷键

为菜单 设置alt+X快捷键

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private final JMenu menu = new JMenu("菜单");
......
// 为菜单设置alt+f快捷键(助记符)
menu.setMnemonic('F');
......

为菜单项设置组合快捷键

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private final JMenuItem menuItem = new JMenuItem("退出");
........
menuItem.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e)
    {
        dispose();
    }
});
// 为菜单项设置Ctrl+Shif+W快捷键
KeyStroke Ctrl_Shift_W = KeyStroke.getKeyStroke(KeyEvent.VK_W, KeyEvent.CTRL_DOWN_MASK + KeyEvent.SHIFT_DOWN_MASK);
menuItem.setAccelerator(Ctrl_Shift_W);
........

为按钮设置Ctrl+xxx组合快捷键

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......
// 反转数组按钮的时间监听器
private final class ReverseButtonListener implements ActionListener
{
    public void actionPerformed(ActionEvent e)
    {
        String[] arrayStrs = textAreaInput.getText().split(",");
        int[] array = new int[arrayStrs.length];
        for (int i = 0; i < array.length; i++)
        {
            array[i] = Integer.parseInt(arrayStrs[i]);
        }
        reverseArray(array);
    }
    private void reverseArray(int[] array)
    {
        int temp;
        int i_thFromLast;
        for (int i = 0; i < array.length / 2; i++)
        {
            // 计算倒数第i个元素的索引
            i_thFromLast = array.length - 1 - i;
            // 将第i个元素和倒数第i个元素交换
            temp = array[i];
            array[i] = array[i_thFromLast];
            array[i_thFromLast] = temp;
            printSwapStep(array, i_thFromLast, i);
        }
    }
    private void printSwapStep(int[] array, int i_thFromLast, int i)
    {
        for (int j = 0; j < array.length; j++)
        {
            if (j == i)
            {
                textAreaShow.append("[");
            }
            textAreaShow.append(String.valueOf(array[j]));
            if (j == i_thFromLast)
            {
                textAreaShow.append("]");
            }
            if (j < array.length - 1)
            {
                textAreaShow.append(",");
            }
        }
        textAreaShow.append("\n");
    }
}
......
JButton buttonReverse = new JButton("反转数组");
// 为按钮设置事件监听器
buttonReverse.addActionListener(new ReverseButtonListener());
// 为按钮绑定组合快捷键
buttonReverse.registerKeyboardAction(new ReverseButtonListener(), KeyStroke.getKeyStroke(KeyEvent.VK_B, KeyEvent.CTRL_DOWN_MASK),
        JComponent.WHEN_IN_FOCUSED_WINDOW);
......