按钮不会显示在FlowLayout中

Question

我正在制作一个课程。该想法是显示图像和上/下对比度。这里是例子。我能够让图像出现，图像上方出现一个灰色条，就像示例中那样，但是我的按钮不在那里。我不知道如何通过FlowLayout正确地做到这一点，或者如果我需要使用其他布局。我是GUI新手，所以任何帮助将不胜感激！

这是我的样子。我究竟做错了什么？

import javax.imageio.ImageIO; 
import javax.swing.*; 

import java.util.*; 
import java.io.*; 
import java.awt.*; 
import java.awt.image.*; 
import java.awt.event.*; 
import java.applet.Applet; 

/** 
* This class extends JPanel and can load an image to its 
* original size. 
* 
* @author Dahai Guo 
* 
*/ 
class ImagePanel extends JPanel{ 
    private BufferedImage image; 

    public ImagePanel(BufferedImage image){ 
     this.image=image; 
    } 

    /** 
    * Draws the image. 
    */ 
    public void paintComponent(Graphics g){ 
     super.paintComponent(g); 
     g.drawImage(image,0,0,image.getWidth(),image.getHeight(),this); 

    } 
} 

/** 
* Object of this class can load an image and enable the user 
* to increase and decrease the contrast of the image. 
* 
* Note this class can only deal with the contrast of gray levels 
* 
* @author Dahai Guo 
* 
*/ 
public class HistgramEqualizerApp extends JFrame { 

    int count=0; 

    private FlowLayout myLayout; 
    private BorderLayout borderLayout; 
    private ImagePanel imagePanel; 
    private JButton increaseContrastButton; 
    private JButton decreaseContrastButton; 
    private BufferedImage image; 

    /** 
    * Cummulative density function 
    */ 
    private int [] cdf=new int[256]; 

    /** 
    * The current largest gray level. 
    */ 
    private int imageMaxGrayLevel=0; 

    /** 
    * The current smallest gray level. 
    */ 
    private int imageMinGrayLevel=300; 

    /** 
    * The smallest nonzero cell in the CDF of gray level 
    * of the image. 
    */ 
    private int minCdfValue; 

    /** 
    * The largest gray level when the image is first loaded. 
    */ 
    private int originalImageMaxGray; 

    /** 
    * The smallest gray level when the image is first loaded. 
    */ 
    private int originalImageMinGray; 

    private int MAX_GRAY_LEVEL=255; 
    private int MIN_GRAY_LEVEL=0; 


    /** 
    * Sets up the GUI components and register the action listener for 
    * the two buttons for increasing and decreasing contrast 
    * @param filename the filename of the image 
    * @throws IOException thrown when problems occurs when loading the image 
    */ 
    public HistgramEqualizerApp(String filename) 
     throws IOException{ 
     // insert your code 

     try { 
      image = ImageIO.read(new File(filename)); 
     } catch (IOException e) { 
      System.err.println("Problem loading image."); 
      System.exit(1); 
     } 
     // Display image to screen 
     add(new JLabel(new ImageIcon(filename))); 



     myLayout = new FlowLayout(FlowLayout.CENTER, 20, 40); 
     setLayout(myLayout);      

     // Buttons for contrast control 
     increaseContrastButton = new JButton(">>"); 
     decreaseContrastButton = new JButton("<<"); 

     add(increaseContrastButton); 
     increaseContrastButton.setVisible(true); 

     add(decreaseContrastButton);  
     decreaseContrastButton.setVisible(true); 


     //increaseContrastButton.addActionListener(this); 
     //decreaseContrastButton.addActionListener(this); 








    } 

    /** 
    * Calculates the current image's CDF. 
    * 
    * There are only 256 gray levels in consideration. The image is scanned 
    * pixel by pixel. For each pixel, its gray level is the average of its rgb. 
    * This gray level will be used to generate a histogram. 
    * 
    * When the histogram is ready, 
    * CDF[i]=sum(histogram[0]+histogram[1]+...+histogram[i]). 
    * 
    * Note this method is also in charge of calculating the following instance variable: 
    * <ul> 
    * <li>imageMaxGrayLevel</li> 
    * <li>imageMinGrayLevel</li> 
    * <li>minCdfCell</li> 
    * </ul> 
    */ 
    private void findCdf(){ 

     // insert your code 
    } 

    /** 
    * Finds the rgb of a pixel in image. 
    * 
    * @param image the source image 
    * @param x horizontal coordinate 
    * @param y vertical coordinate 
    * @param rgb an array where the result is saved 
    */ 
    private void getRGB(BufferedImage image, int x, int y, int[] rgb){ 
     int temp=image.getRGB(x,y); 
     Color color=new Color(temp); 
     rgb[0]=color.getRed(); 
     rgb[1]=color.getGreen(); 
     rgb[2]=color.getBlue(); 
    } 

    /** 
    * Sets the rgb values for a pixel of image 
    * 
    * @param image source image 
    * @param x horizontal coordinate 
    * @param y vertical coordinate 
    * @param rgb the rgb values to set 
    */ 
    private void setRGB(BufferedImage image, int x, int y, int[] rgb){ 
     Color color=new Color(rgb[0],rgb[1],rgb[2]); 
     image.setRGB(x, y, color.getRGB()); 
    } 

    /** 
    * Inner class that handles the event on increaseContrastButton and 
    * decreaseContrastButton. 
    * 
    * @author Dahai Guo 
    * 
    */ 
    private class ChangeConstrastListener implements ActionListener{ 

     /** 
     * This variable decides how fast the contrast is changing. 
     * 
     * When increasing contrast, the largest/smallest gray level will 
     * be increased/decreased STEP. 
     * 
     * When decreasing contrast, the largest/smallest gray level will 
     * be decrease/increase STEP. 
     */ 
     private int STEP=10; 

     /** 
     * Is the method that deals with both increaseContrastButton and 
     * decreaseContrastButton. 
     */ 
     @Override 
     public void actionPerformed(ActionEvent e){ 

      // insert your code 

      imagePanel.repaint(); 
     } 


     /** 
     * Changes the contrast for each pixel of the image which 
     * is defined in the outer class. 
     * @param maxGray 
     * @param minGray 
     */ 
     private void changeConstrast(int maxGray, int minGray){ 

      int width=image.getWidth(); 
      int height=image.getHeight(); 
      int rgb[]=new int[3]; 
      for(int i=0;i<width;i++){ 
       for(int j=0;j<height;j++){ 
        equalize(i,j,maxGray,minGray); 
       } 
      } 

      findCdf(); 
     } 

     /** 
     * Follows "Histogram Equalization" on Wikipedia. 
     * 
     * Changes the rgb for the pixel at (x,y) in the image. 
     * 
     * @param x horizontal coordinate 
     * @param y vertical coordinate 
     * @param max the new max gray level 
     * @param min the new min gray level 
     */ 
     private void equalize(int x, int y, int max, int min){ 

      // insert your code here 

     } 
    } 

    public static void main(String args[]) 
     throws IOException{ 
     if(args.length!=1){ 
      System.err.println("Missing the path to an image file"); 
      System.err.println("Command: java HistogramEqualizer image_file"); 
      System.exit(1); 
     } 
     HistgramEqualizerApp histApp = new HistgramEqualizerApp(args[0]); 

     histApp.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     histApp.setSize(512, 400); // set frame size 
     histApp.setVisible(true); // display frame 
     histApp.setResizable(true); 
    } 


} 

Answer 1

这里是使其工作的一种方式：

public class HistgramEqualizerApp extends JFrame { 

    private JButton increaseContrastButton = new JButton(">>");; 
    private JButton decreaseContrastButton = new JButton("<<");; 

    public HistgramEqualizerApp(String filename) throws IOException { 

     JPanel buttonsPanel = new JPanel(new FlowLayout(FlowLayout.CENTER, 20, 40)); 
     buttonsPanel.add(decreaseContrastButton); 
     buttonsPanel.add(increaseContrastButton); 
     getContentPane().add(new JLabel(new ImageIcon(filename))); 
     getContentPane().add(buttonsPanel, BorderLayout.PAGE_START); 
    } 

    public static void main(String args[]) throws IOException { 

     HistgramEqualizerApp histApp = new HistgramEqualizerApp(args[0]); 
     histApp.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     histApp.pack(); 
     histApp.setVisible(true); 
    } 
} 

Answer 2

这是我的两分钱。

如前所述：“您应该使用边框布局并将按钮添加到面板，然后将所述面板添加到主框架，然后将图像面板添加到中心。”

import java.awt.*; 
import java.io.IOException; 
import java.util.Arrays; 
import java.util.List; 
import javax.swing.*; 

@SuppressWarnings("serial") 
public class HistogramEqualizerApp extends JFrame { 
    private ButtonPanel buttonPanel; 
    private ImagePanel imagePanel; 

    private JButton increaseContrastButton; 
    private JButton decreaseContrastButton; 
    private BufferedImage image; 

    public HistgramEqualizerApp() { 
     Container content = this.getContentPane(); 
     content.setLayout(new BorderLayout()); 

     // Buttons for contrast control 
     increaseContrastButton = new JButton(">>"); 
     decreaseContrastButton = new JButton("<<"); 
     buttonPanel = new ButtonPanel(
       Arrays.asList(decreaseContrastButton, increaseContrastButton)); 
     content.add(buttonPanel, BorderLayout.NORTH); 

     image = randomImage(80, 120, 4); 
     imagePanel = new ImagePanel(image); 
     content.add(imagePanel, BorderLayout.CENTER); 

     this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     this.setSize(512, 400); 
     this.setResizable(true); 
    } 

    public static void main(String args[]) throws IOException { 
     SwingUtilities.invokeLater(new Runnable() { 
      @Override 
      public void run() { 
       HistgramEqualizerApp histApp = new HistgramEqualizerApp(); 
       histApp.setVisible(true); 
      } 
     }); 
    } 

    static class ImagePanel extends JPanel { 
     private BufferedImage image; 

     public ImagePanel(BufferedImage image) { 
      this.image = image; 
     } 

     @Override 
     public void paintComponent(Graphics g) { 
      super.paintComponent(g); 
      g.drawImage(image, 0, 0, image.getWidth(), image.getHeight(), this); 

     } 
    } 

    static class ButtonPanel extends JPanel { 
     private List<JButton> buttons; 

     public ButtonPanel(List<JButton> buttons) { 
      this.setLayout(new FlowLayout()); 
      this.buttons = buttons; 
      for (JButton button : buttons) { 
       this.add(button); 
      } 
     } 
    } 

    public static BufferedImage randomImage(int rows, int cols, int pixelRatio) { 
     int width = pixelRatio * cols, height = pixelRatio * rows; 
     BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_3BYTE_BGR); 
     Graphics2D g = (Graphics2D) img.getGraphics(); 
     int x, y = 0; 
     for (int i = 0; i < rows; i++) { 
      for (int j = 0; j < cols; j++) { 
       x = i * pixelRatio; 
       y = j * pixelRatio; 
       if ((i * j) % 6 == 0) { 
        g.setColor(Color.GRAY); 
       } else if ((i + j) % 5 == 0) { 
        g.setColor(Color.BLUE); 
       } else { 
        g.setColor(Color.WHITE); 
       } 
       g.fillRect(y, x, pixelRatio, pixelRatio); 
      } 
     } 
     g.dispose(); 

     return img; 
    } 
}