Java Swing实现多窗口

程序多窗口功能研究，代码来源于一位大佬的Java教材。

??Gives a program that creates a main window with a text area in the scroll pane
and a button named Show Histogram. When the user clicks the button, a new window appears
that displays a histogram to show the occurrences of the letters in the text area. Figure 17.15
contains a sample run of the program.

??编写一个程序，创建一个主窗口，页面包含文本区域嵌套在滚动面板中，一个按钮名字为显示直方图，当用户点击按钮，一个新的窗口出现，显示的是一个直方图，统计文本区域中每个字符的出现次数，下图显示的是程序运行效果。

程序实现

Main Window

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

public class MultipleWindowDemo extends JFrame {
    private JTextArea jta = new JTextArea();
    private JButton jbtShowHistogram = new JButton("Show Histogram");
    Histogram histogram = new Histogram();

    private String content = "Write a program that creates a main window with " +
            "a text area in the scroll pane and a button named \"Show Histogram\"." +
            "When the user clicks the button, a new window appears that displays "+
            "a histogram to show the occurrence of the letters in the text area." +
            "Figure 13.31 contains a sample run of the program.";
//    private String content = "编写一个程序，创建一个主窗口，页面包含文本区域嵌套在滚动面板中，一个按钮名字为显示直方图" +
//        "当用户点击按钮，一个新的窗口出现，显示的是一个直方图，统计文本区域中每个字符的出现次数，图13.31显示的是程序运行效果";

    // Create a new frame to hold the histogram panel
    private JFrame histogramFrame = new JFrame();

    public MultipleWindowDemo() throws HeadlessException {
        // Store text area in a scroll pane
        JScrollPane scrollPane = new JScrollPane(jta = new JTextArea());
        scrollPane.setPreferredSize(new Dimension(300, 200));

        jta.setLineWrap(true);
        jta.setWrapStyleWord(true);

        add(scrollPane, BorderLayout.CENTER);
        add(jbtShowHistogram, BorderLayout.SOUTH);

        jta.setText(content);

        jbtShowHistogram.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                int[] count = countLetters();

                // Set the letter count to histogram for display
                histogram.setHistogram(count);

                // Show the frame
                histogramFrame.setVisible(true);
            }
        });

        histogramFrame.add(histogram);
        histogramFrame.pack();
        histogramFrame.setTitle("Histogram");
    }

    /** Count the letters in the text area */
    public int[] countLetters() {
        int[] count = new int[26];

        String text = jta.getText();

        for (int i = 0; i < text.length(); i++) {
            char character = text.charAt(i);
            if (character >= 'a' && character <= 'z')
                count[character - 'a']++;
            else if (character >= 'A' && character <= 'Z')
                count[character - 'A']++;
        }

        return count;// Return the count array
    }

    public static void main(String[] args) {
        MultipleWindowDemo frame = new MultipleWindowDemo();
        frame.setTitle("MultipleWindowDemo");
        //frame.pack();
        frame.setSize(300, 350);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

}

Histogram(直方图)

package learn2;

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

public class Histogram extends JPanel {
    // Count the occurrences of 26 letters
    int[] count;

    public Histogram() {
    }

    public void setHistogram(int[] count) {
        this.count = count;
        repaint();
    }

    @Override
    protected void paintComponent(Graphics g) {
        if (count == null) // no display if count is null
            return;

        super.paintComponent(g);

        // Find the panel size and bar width and interval dynamically
        int width = getWidth();
        int height = getHeight();
        int interval = (width - 40) / count.length;
        int individualWidth = (int) ((width - 40) / 24 * 0.60);

        // Find the maximum count. The maximum count has the highest bar
        int maxCount=0;
        for (int i = 0; i < count.length; i++) {
            if (count[i] > maxCount){
                maxCount = count[i];
            }
        }

        // X is the start position for the first bar in the histogram
        int x = 20;

        // Draw a horizontal base line
        g.drawLine(10, height - 45, width - 10, height - 45);
        for (int i = 0; i < count.length; i++) {
            // find the bar height
            int barHeight = (int) (((double)count[i] / (double) maxCount) * (height - 55));

            // Display a bar (i.e. rectangle)
            g.drawRect(x, height - 45 - barHeight, individualWidth, barHeight);

            // Display a letter under the base line
            g.drawString(String.valueOf((char)(65 + i)), x, height - 30);
            x += interval;
        }
    }
    @Override
    public Dimension getPreferredSize() {
        return new Dimension(300, 300);
    }

}

总结

??在程序开发中有时候需要实现多个窗口，比如打开一个窗口实现特定的任务，在游戏开发中，可以实现一个主窗口，显示一些基本操作，游戏简介等，游戏窗口就可以创建一个新窗口，负责游戏的渲染和交互。

??当然不止游戏，许多程序都有多窗口的需求，可以根据需要来实现。

??Java Swing的JPanel相当于Android中的View类，paintComponent(Graphics g)方法相当于onDraw(Canvas c)方法，一般用于实现一些自定义的绘制需求。JPanel还可以充当子面板，用于实现一些较复杂的页面布局。