我可以更改在代码中放在JLabel上的ImageIcon的位置吗？

Question

I tried using, "label.setBounds(100,100,250,250)" and "label.setLocation(100,100)" but the image does not move from the top and center of the JLabel.

import java.awt.Dimension;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class Machine extends JPanel
{
    public Machine()
    {
         ImageIcon imageIcon = new ImageIcon("res/robot.png");
         JLabel label = new JLabel(imageIcon);
         add(label);
    }

     public static void main(String[] args)
     {
         JFrame frame = new JFrame();
         frame.add(new Machine());
         frame.setVisible(true);
         frame.setSize(new Dimension(1080, 720));
     }
}

Answer 1

What are you trying to do?

The default layout of a JPanel is a FlowLayout with center alignment and the label is displayed at its preferred size. So the label is displayed in the center.

You have a couple of options:

1. Change the alignment of the FlowLayout to be either LEFT or RIGHT

2. Don't add the label to the panel. Just add it directly to the frame which uses a BorderLayout .

Then you can do something like:

 label.setHorizontalAlignment(JLabel.LEFT);
 label.setVerticalAlignment(JLabel.CENTER);

Edit:

was just trying to get the image to be in the middle of the frame

Then post your actual requirement when you ask a question. We don't know what "can I change the location" means to you.

So you would either use the BorderLayout and adjust the horizontal/vertical alignment as already demonstrated.

Or, you could set the layout manager of the frame to be a GridBagLayout and then add the label directly to the frame and use:

frame.add(label, new GridBagConstraints());

Now the label will move dynamically as the frame is resized.

Answer 2

If you want to place an image in a certain location, perhaps best is to draw it directly in your JPanel in a paintComponent method override, using one of Graphics drawImage(...) methods, one that allows placement of the image.

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;

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

@SuppressWarnings("serial")
public class Machine extends JPanel {
    private static final String IMG_PATH = "https://upload.wikimedia.org/wikipedia/commons/"
            + "thumb/f/f2/Abraham_Lincoln_O-55%2C_1861-crop.jpg/"
            + "250px-Abraham_Lincoln_O-55%2C_1861-crop.jpg";
    private BufferedImage img;
    private int x;
    private int y;

    public Machine() {
        setPreferredSize(new Dimension(1080, 720));
        x = 100; // or wherever you want to draw the image
        y = 100; 

        try {
            URL imgUrl = new URL(IMG_PATH);
            img = ImageIO.read(imgUrl);
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(-1);
        }
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        if (img != null) {
            g.drawImage(img, x, y, this);
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            JFrame frame = new JFrame();
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.add(new Machine());
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        });
    }
}

Version 2: MouseListener / MouseMotionListener so that the image can be moved

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;

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

@SuppressWarnings("serial")
public class Machine extends JPanel {
    private static final String IMG_PATH = "https://upload.wikimedia.org/"
            + "wikipedia/commons/thumb/f/f2/"
            + "Abraham_Lincoln_O-55%2C_1861-crop.jpg/" 
            + "250px-Abraham_Lincoln_O-55%2C_1861-crop.jpg";
    private BufferedImage img;
    private int x;
    private int y;

    public Machine() {
        setPreferredSize(new Dimension(1080, 720));
        x = 100; // or wherever you want to draw the image
        y = 100;

        MyMouse mouse = new MyMouse();
        addMouseListener(mouse);
        addMouseMotionListener(mouse);

        try {
            URL imgUrl = new URL(IMG_PATH);
            img = ImageIO.read(imgUrl);
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(-1);
        }
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        if (img != null) {
            g.drawImage(img, x, y, this);
        }
    }

    private class MyMouse extends MouseAdapter {
        private Point offset;

        @Override
        public void mousePressed(MouseEvent e) {
            // check if left mouse button pushed
            if (e.getButton() != MouseEvent.BUTTON1) {
                return;
            }

            // get bounds of the image and see if mouse press within bounds
            Rectangle r = new Rectangle(x, y, img.getWidth(), img.getHeight());
            if (r.contains(e.getPoint())) {
                // set the offset of the mouse from the left upper 
                // edge of the image
                offset = new Point(e.getX() - x, e.getY() - y);
            }
        }

        @Override
        public void mouseDragged(MouseEvent e) {
            if (offset != null) {
                moveImg(e);
            }
        }

        @Override
        public void mouseReleased(MouseEvent e) {
            if (offset != null) {
                moveImg(e);
            }
            offset = null;
        }

        private void moveImg(MouseEvent e) {
            x = e.getX() - offset.x;
            y = e.getY() - offset.y;
            repaint();
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            JFrame frame = new JFrame();
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.add(new Machine());
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        });
    }
}