Java JLabel不会重新定位

Question

I want to set my jLabel above the jButton. In fact, it would be ideal if they would just "float" above eachother.

Jet, I can't get the label to display because it stays below the button. I have been googling and trying things like setLocation, but to no avail. I'm sure this is something super basic that I'm missing...

    public class TranceExperiment extends JFrame {

        public TranceExperiment() {

            setTitle("Simple example");
            setSize(600, 400);
            setLocationRelativeTo(null);
            setDefaultCloseOperation(EXIT_ON_CLOSE);
        }


        public static void main(String[] args) {

            EventQueue.invokeLater(new Runnable() {
                @Override
                public void run() {
                    TranceExperiment ex = new TranceExperiment();
                    ex.setVisible(true);

                    //set startLabel
                    JLabel expText = new JLabel("Welcome to the experiment");
                    ex.add(expText);
                    expText.setLocation(200,200);
                    //expText.setSize(100, 100);
                   expText.setVisible(true);
//                    expText.setLayout(null);
                    ex.add(expText);


                    //start Button
                    final JButton startButton = new JButton("Start");
                    startButton.addActionListener(new ActionListener() {
                        @Override
                        public void actionPerformed(ActionEvent event) {
                            //do stuff

                            startButton.setText("Continue");

                        }

                    });

                    ex.add(startButton);

                }
            });
        }
    }

Answer 1

You have to use Layout managers if you want neatly spaced layouts. There are a variety of these including FlowLayout, BorderLayout and GridLayout . I would advise using GridLayout for this particular problem, for example:

ex.setLayout(new GridLayout(3,1));

The 3 is for rows and the 1 is for columns. Insert this line before you add the button and label to the frame.

EDIT:

You can also add a JPanel to your frame and then set the layout of the panel to GridLayout, like so:

ex.setLayout(new BorderLayout());
JPanel panel = new JPanel();
panel.setLayout(new GridLayout(3,1));
panel.add(startButton);
ex.add(panel, BorderLayout.NORTH);

By using BorderLayout you can position your panel anywhere in the frame. Just remember to set the size of the panel and/or the frame, and also to add the other labels to the panel. BorderLayout has a couple of settings you can play around with including SOUTH, CENTER, EAST and WEST.

Answer 2

The easiest way to achieve your goal is to use WindowBuilder , a plugin for Eclipse ( https://eclipse.org/windowbuilder/ ).

First select GroupLayout from the list of available layouts.

Then put your jLabel above your jButton and select " Anchored Bottom ". The plugin will generate the code for you.

Answer 3

Use Layout, Luke! :) I like GridBagLayout, because it is very flexible.

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

public class Main {

public static void main(String[] args) {
    System.out.println("Hello World!");
    final JFrame frame = new JFrame();
    frame.setTitle("Simple example");
    frame.setSize(600, 400);
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    frame.setVisible(true);
    frame.setLayout(new BorderLayout());

    JPanel contentPanel = new JPanel(new GridBagLayout());
    frame.add(contentPanel);

    JLabel expText = new JLabel("Welcome to the experiment");
    expText.setPreferredSize(new Dimension(150, 40));
    expText.setVisible(true);

    final JButton startButton = new JButton("Start");
    startButton.setPreferredSize(new Dimension(450, 40));
    startButton.setPreferredSize(new Dimension(450, 40));
    startButton.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent event) {
            startButton.setText("Continue");
        }

    });

    contentPanel.add(expText, new GridBagConstraints(0, 0, 1, 1, 1, 0, GridBagConstraints.NORTHWEST,
            GridBagConstraints.HORIZONTAL, new Insets(0, 200, 0, 100), 0, 0));
    contentPanel.add(startButton, new GridBagConstraints(0, 1, 1, 1, 1, 0, GridBagConstraints.NORTHWEST,
            GridBagConstraints.HORIZONTAL, new Insets(0, 0, 0, 0), 0, 0));
    contentPanel.add(Box.createVerticalGlue(), new GridBagConstraints(0, 1, 2, 2, 1, 1,
            GridBagConstraints.NORTHWEST, GridBagConstraints.BOTH, new Insets(0, 0, 0, 0), 0, 0));
    }
}

Answer 4

setLocation and setSize are not meant to be called by you, user of the frame. They are meant to be called by the layout manager which is associated to the container of the component.

You can find comprehensive and detailed information about how layout management works on the Java website: http://docs.oracle.com/javase/tutorial/uiswing/layout/visual.html

To obtain what you want, a SpringLayout seems more appropriate.

As an alternative, if you want to directly call setLocation and setSize , you should remove the layout manager, by setting it to null .