如何使元素根据JAVA swing中窗口的大小自动调整其大小？

Question

The IDE I use is Intellij. Here I created a small program of converting currency. I used BorderLayout as the root panel and flowLayout for the bottom buttons. For west and east panel I used GridLayout(Intellij). When I run the program, it can display normally like this:

After changing its size, the gap between elements begin to expand like this:

How do I make them adjust the distance automatically?

Here are my codes:

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

  /**
   * Created by Bob on 2017/5/11.
   */



 public class layout {

private JPanel converterRootPanel;
private JPanel westPanel;
private JLabel selectNationPanel;
private JLabel currencyToConvett;
private JLabel currencyConverted;
private JComboBox currencyType;
private JTextField input;
private JTextField output;
private JPanel eastPanel;
private JPanel southPanel;
private JButton convertButton;
private JButton clearButton;
private JLabel convertToLabel;
private JComboBox convertType;
private JPanel northPanel;
public int selection1;
public int selection2;
public Double toConvert;
public double[][] rate1={{0,0.1335,0.1449,16.5172,163.4922},{7.4927,0,1.0857,123.7900,
        1225.0380},{6.9029,0.9382,0,114.01,1129.19},{0.06053,0.00808,0.008771,0,9.9043},{0.006112,
        0.0008158,0.0008856,0.101,0}};

public layout() {
    currencyType.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            selection1 = currencyType.getSelectedIndex();
        }
    });
    convertType.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            selection2 = convertType.getSelectedIndex();
        }
    });

    convertButton.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            if(selection1==selection2){
                JOptionPane.showConfirmDialog(null, "You have to choose different currency types!", "Error Alert", JOptionPane.CANCEL_OPTION);
            }
            output.setText("");
            toConvert = Double.parseDouble(input.getText().toString());
            Double convertResult = toConvert*rate1[selection1][selection2];
            output.setText(convertResult.toString());
        }
    });
    clearButton.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            output.setText("");
            input.setText("");
            convertType.setSelectedIndex(0);
            currencyType.setSelectedIndex(0);
        }
    });
}

public static void main(String[] args) {
    JFrame frame = new JFrame("layout");
    frame.setContentPane(new layout().converterRootPanel);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setVisible(true);
    //layout lay = new layout();
}

private void createUIComponents() {
    // TODO: place custom component creation code here
}

}

Answer 1

What you want to do is done through a layout manager. There are several of these for Java that are part of the standard library and there are also other custom ones such as MigLayout.

The Java tutorials have a whole section on layout managers here

---

A basic example of the GridBagLayout would be the following.

import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class Basic {
    JFrame frame;
    JPanel panel;
    JLabel label;
    JButton button;

    public void createAndRun() {
        frame = new JFrame("Basic Example");

        setUp();
        frame.getContentPane().add(panel);

        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private void setUp() {
        panel = new JPanel(new GridBagLayout());
        GridBagConstraints c = new GridBagConstraints();

        label = new JLabel("I am a JLabel");
        c.gridx = 0;
        c.gridy = 0;
        c.fill = GridBagConstraints.BOTH;
        c.weightx = 0.5;
        c.weighty = 0;
        panel.add(label, c);

        button = new JButton("I am a JButton");
        c.gridx = 0;
        c.gridy = 1;
        c.weighty = 0.5;
        panel.add(button, c);
    }

    public static void main(String[] args) {
        Basic b = new Basic();
        b.createAndRun();
    }
}

However, as the tutorials put it.

"GridBagLayout is one of the most flexible — and complex — layout managers the Java platform provides."

So if you are having problems with GridBagLayout it may be worth looking at other layout managers beforehand.

---

Finally, I would like to suggest some ways that you might look at improving your code.

The part that caught my eye the most was this line.

frame.setContentPane(new layout().converterRootPanel);

I would recommend not creating the JFrame and initialising you Layout class in the main method. Instead, it would be worth initialising the class first and then calling a method to create the frame.

Layout l = new Layout();
l.createFrame();

This is shown in the example code above.

Answer 2

A GridBagLayout uses the weightx and weighty properties of GridBagConstraints to determine how extra space is distributed. GridBagLayout uses the largest weightx of all cells in a column to determine the column's actual horizontal weight for all cells in that column, and similarly, the largest weighty of all cells in a row determines that row's vertical weight. If all columns have a zero weightx, they are all centered horizontally. If all rows have a zero weighty, they are all centered vertically.

Usually a good design is to have the input fields stretch horizontally, while the labels remain the same size at all times. You probably want the rows to have same vertical spacing at all times, and have all extra space appear above or below the entire set of rows.

To make all cells of a particular column stretch, you only need to set the weightx of one cell in that column:

JPanel buttonPanel = new JPanel();
buttonPanel.add(convertButton);
buttonPanel.add(clearButton);

converterRootPanel = new JPanel(new GridBagLayout());

GridBagConstraints gbc = new GridBagConstraints();
gbc.anchor = GridBagConstraints.LINE_END;

// First row

converterRootPanel.add(selectNationPanel, gbc);

gbc.weightx = 1;

gbc.gridwidth = GridBagConstraints.REMAINDER;
gbc.fill = GridBagConstraints.HORIZONTAL;
converterRootPanel.add(currencyType, gbc);

gbc.weightx = 0;
gbc.insets.top = 3;

// Second row

gbc.gridwidth = 1;
gbc.fill = GridBagConstraints.NONE;
converterRootPanel.add(convertToLabel, gbc);

gbc.gridwidth = GridBagConstraints.REMAINDER;
gbc.fill = GridBagConstraints.HORIZONTAL;
converterRootPanel.add(convertType, gbc);

// Third row

gbc.gridwidth = 1;
gbc.fill = GridBagConstraints.NONE;
converterRootPanel.add(currencyToConvett, gbc);

gbc.gridwidth = GridBagConstraints.REMAINDER;
gbc.fill = GridBagConstraints.HORIZONTAL;
converterRootPanel.add(input, gbc);

// Fourth row

gbc.gridwidth = 1;
gbc.fill = GridBagConstraints.NONE;
converterRootPanel.add(currencyConverted, gbc);

gbc.gridwidth = GridBagConstraints.REMAINDER;
gbc.fill = GridBagConstraints.HORIZONTAL;
converterRootPanel.add(output, gbc);

// Button row

gbc.fill = GridBagConstraints.NONE;
gbc.anchor = GridBagConstraints.CENTER;
converterRootPanel.add(buttonPanel, gbc);