JFrame在重绘时不刷新

Question

I have written a small code for simple resizing of any image on my system in java using SWING.

http://ideone.com/9vii2E

import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.filechooser.FileNameExtensionFilter;

class T extends JPanel implements ActionListener {
    /**
     * 
     */
    private static final long serialVersionUID = -2900955352094956729L;
    int x = 0;
    int flag = 0;
    BufferedImage b;
    Image z;
    JButton j, a, cl;
    JTextField ht, wdth;

    T() {
        j = new JButton("Hi");
        a = new JButton("Resizze");
        a.addActionListener(this);
        add(a);
        j.addActionListener(this);
        add(j);
        setBackground(Color.WHITE);

    }

    class tobi implements ActionListener {// for close button of second window
        public void actionPerformed(ActionEvent asd) {
            // if(x==1)
            {
                int gadda = 100, w = 100;
                gadda = Integer.parseInt(ht.getText());
                w = Integer.parseInt(wdth.getText());
                z = z.getScaledInstance(gadda, w, Image.SCALE_SMOOTH);
                setBackground(Color.BLACK);
                j.repaint();
                JButton ttr = (JButton) asd.getSource();
                Window qwe = SwingUtilities.windowForComponent(ttr);
                qwe.setVisible(false);
            }
        }

    }

    public void meth()// method to create second window
    {
        JFrame win = new JFrame();
        win.setTitle("resizze!!");
        win.setLayout(new FlowLayout());
        JLabel height = new JLabel("Height:");
        ht = new JTextField(20);

        JLabel width = new JLabel("Width:");
        wdth = new JTextField(20);
        JButton cl = new JButton("close");

        cl.addActionListener(new tobi());
        win.add(height);
        win.add(ht);
        win.add(width);
        win.add(wdth);
        win.add(cl);
        win.pack();
        win.setVisible(true);
    }

    public void paintComponent(Graphics g) {

        Graphics2D gt = (Graphics2D) g;
        super.paintComponent(g);
        if (x == 1)
            g.drawImage(z, 0, 0, null);
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == j) {
            JFileChooser q = new JFileChooser();
            // q.setFileFilter(new
            // FileNameExtensionFilter("Image Files",ImageIO.getReaderFileSuffixes()));
            q.addChoosableFileFilter(new FileNameExtensionFilter("Image Files",
                    "jpg", "jpeg", "png"));
            int option = q.showOpenDialog(null);
            if (option == JFileChooser.APPROVE_OPTION) {
                File f = q.getSelectedFile();
                try {
                    b = ImageIO.read(f);
                    z = b.getScaledInstance(100, 100, Image.SCALE_SMOOTH);
                } catch (IOException ae) {
                }
            }
            x = 1;
            repaint();
        }

        else if (e.getSource() == a) {
            meth();
        }

    }

    public static void main(String args[]) {
        SwingUtilities.invokeLater(new Runnable(){
    public void run(){
    JFrame j = new JFrame();
        j.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        j.setSize(500, 500);
        j.add(new T());
        j.setVisible(true);
    j.revalidate();
    j.repaint();

}
});
    }
}

I am asking user to upload the image file and then taking parameters height and width for resizing. After clicking on close button in second window,nothing happens(except for first few times),while the image on first window should be repainted. (Sorry for bad variable names and formatting)

Answer 1

You have a whole bunch of issues, variable naming only been one of them...

g.drawImage(z, 0, 0, null); should be g.drawImage(z, 0, 0, this); , this ensures that if the image is still be processed for some reason, the component can respond to any of it's changes and update schedule new repaints of it's own accord

Don't ignore exceptions

try {
    b = ImageIO.read(f);
    z = b.getScaledInstance(100, 100, Image.SCALE_SMOOTH);
} catch (IOException ae) {

}

should be (at the very least)

try {
    b = ImageIO.read(f);
    z = b.getScaledInstance(100, 100, Image.SCALE_SMOOTH);
} catch (IOException ae) {
    ae.printStackTrace();
}

This will help you solve probable issues in your code.

I'd also change the above to

try {
    b = ImageIO.read(f);
    z = b;
} catch (IOException ae) {
    ae.printStackTrace();
}

so you are presented with the original image first (this is just my opinion), but since you don't have any real scaling properties at this point, it makes sense to me.

You're shadowing the cl variable, declaring it as a instance field, but re-declaring it again as a local variable in meth . I don't if this will be an issue, but you need to be aware of it.

z = z.getScaledInstance(gadda, w, Image.SCALE_SMOOTH); should be z = b.getScaledInstance(gadda, w, Image.SCALE_SMOOTH); . You want to scale from the source, otherwise you are going to have a lot of pixelation issues.

You also calling j.repaint(); which is just repainting the button, which is clearly not what you want to do, instead you should just be calling repaint() on the panel itself

You should also have a look at The Perils of Image.getScaledInstance() and this example and this example for examples of how you might produce better scaling operations