java jframe中的按钮不会调整大小吗？

Question

I started java programming yesterday, and have developed this. I have run into a problem, as the button will not resize. Please help if you can and thank you in advance.

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

import javax.swing.*;

class BgPanel extends JPanel {
Image bg = new ImageIcon("C:\\Users\\********\\Pictures\\tiger.jpg").getImage();
@Override
public void paintComponent(Graphics g) {
    g.drawImage(bg, 0, 0, getWidth(), getHeight(), this);
     }
}

public class FrameTestBase extends JFrame {
public static void main(String args[]) {
    JPanel bgPanel = new BgPanel();
    bgPanel.setLayout(new BorderLayout());

    final FrameTestBase t = new FrameTestBase();
    ImageIcon img = new ImageIcon("C:\\Users\\********\\Pictures\\gear-icon.png");
    t.setLayout(null);
    t.setIconImage(img.getImage());
    t.setTitle("Login");
    t.setSize(600,600);
    t.setLocationRelativeTo(null);
    t.setContentPane(bgPanel);
    t.setDefaultCloseOperation(EXIT_ON_CLOSE);
    t.setVisible(true);

    JButton registerButton = new JButton("register");
    registerButton.setBounds(80, 80, 80, 80);
    t.add(registerButton);
         }
     }   

Answer 1

I have run into a problem, as the button will not resize. Please help if you can and thank you in advance.

 bgPanel.setLayout(new BorderLayout());
 // --------- your other code
 t.setLayout(null);
 //--------------- your other code
 t.setContentPane(bgPanel); // you are setting bgPanel which has BorderLayout
 JButton registerButton = new JButton("register");
 registerButton.setBounds(80, 80, 80, 80);
 t.add(registerButton); // t is the JFrame, your main window

Any JFrame.add(component) will essentially add your component to the content pane of the JFrame. After setting layout to null you have added the bgPanel as content pane to the JFrame, which has BorderLayout as its layout manager. Adding your button to the content pane ie, bgPanel will add your registerButton with BorderLayout.Center constraint. That is why this button is expanding to the size of the screen.

As you are so eager to see an output do the following:

    // registerButton.setBounds(80, 80, 80, 80); comment out this line
    registerButton.setPreferedSize(new Dimension(80, 80));
    t.add(registerButton, BorderLayout.PAGE_START)

Now, About using NULL Layout:

In your own example you have lost to find the reason why the Button is expanding to the window size. In near future you will see that one of your component has head but lost its tail by going outside of the window border. You will see that one of your component is going to jump over the other without no reason. You will see that you have changed a position of component with relative to another component, but it will make relation with other component. Well you will be able to find the issues wasting lost of time and get fixed by setting xxxSize , setLocation , setBounds etc but....

people can be rich in money, they can't be rich in time.

Start learning LayoutManager: Lesson: Laying Out Components Within a Container

Answer 2

Try to use registerButton.setSize(new Dimension(width, height)) instead of setBounds . Remember to replace width and height for new values

And I forget to say the same thing guys are telling you:

The sooner you learn, the better.
Layouts are not difficult, they're actually easy.

Answer 3

Don't use a null layout!!!

Swing was designed to be used with layout managers. And don't forget to follow Mike's suggestion.