Java 小程序布局未按预期显示 o_O

Question

我这学期要参加 Java class，并且正在做一个带回家的测验。在其中我们创建了一个计算器，它应该看起来像附加的第一张图片

如您所见，基本面板应该分为 2 行和 1 列。上面板分为 3 行和 2 列。下面板有 4 个按钮用于执行计算。

为了这个测验，我创建了 2 个文件，WholePanel.java 和 LayoutPanel.java。这是 WholePanel.java:

的代码

package layoutpanel;

import java.awt.BorderLayout;
import static java.awt.BorderLayout.CENTER;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;


/**
 *
 * @author ross satchell
 */

public class WholePanel extends JPanel{
    public JTextField textBox1, textBox2, resultBox;
    public double num1, num2, result;
    public JLabel label1, label2, label3;
    public JButton addButton, subButton, multipButton, dividButton;


public WholePanel(){                            // constructor
    JPanel upperPanel, lowerPanel, subPanel;
    upperPanel = new JPanel();   // the panel for the top section
    lowerPanel = new JPanel();   // the panel for the lower section
    subPanel = new JPanel();     // panel to hold both upperPanel and lowerPanel
    label1 = new JLabel("Enter number 1:");
    label2 = new JLabel("Enter number 2:");
    label3 = new JLabel("Result:");
    textBox1 = new JTextField(10);
    textBox2 = new JTextField(10);
    resultBox = new JTextField(10);
    addButton  =new JButton("+");
    subButton = new JButton("-");
    multipButton = new JButton("*");
    dividButton = new JButton("/");



    upperPanel.setLayout(new GridLayout(3,2));
    upperPanel.add(label1);
    upperPanel.add(textBox1);       // set up layout and 
    upperPanel.add(label2);         // components for upperPanel
    upperPanel.add(textBox2);
    upperPanel.add(label3);
    upperPanel.add(resultBox);

    lowerPanel.setLayout(new FlowLayout());
    lowerPanel.add(addButton);
    lowerPanel.add(subButton);           // set up topLowerPanel 
    lowerPanel.add(multipButton);        // components and layout
    lowerPanel.add(dividButton);

    subPanel.setLayout(new BorderLayout());
    subPanel.add(upperPanel, BorderLayout.NORTH);
    subPanel.add(lowerPanel, BorderLayout.SOUTH);               // add each panel to the main subPanel
    this.add(subPanel);

    addButton.addActionListener(new ButtonListener());      // add button listeners
    subButton.addActionListener(new ButtonListener());      // for each of the 
    multipButton.addActionListener(new ButtonListener());   // four buttons
    dividButton.addActionListener(new ButtonListener());    //
}


private class ButtonListener implements ActionListener{


    public void actionPerformed(ActionEvent e){
        JButton buttonX = (JButton) e.getSource();
        num1 = Double.parseDouble(textBox1.getText());  // read values in textBox1
        num2 = Double.parseDouble(textBox2.getText());  // and textBox2

        if (buttonX == addButton){
            result = num1 + num2;
        }else if (buttonX == subButton){                // performed required calculation
            result = num1 - num2;
        }else if (buttonX == multipButton){
            result = num1 * num2;
        }else if (buttonX == dividButton){
            result = num1 / num2;
        }
        resultBox.setText("" + result);
        }   //  end actionPerformed() method

    }   // end ButtonListener class

}       // end WholePanel class

这里是 LayoutPanel.java

的代码

package layoutpanel;

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

public class LayoutPanel extends JApplet{


public void init(){

WholePanel wholePanel = new WholePanel();
getContentPane().add(wholePanel);
setSize(300,200);
}

当我运行小程序显示为：
如您所见，似乎 topPanel 和 lowerPanel 都位于子面板的顶行。

出于好奇，我尝试将 subPanel 更改为 BorderLayout，并将 topPanel 定位到 NORTH，将 lowerPanel 定位到 SOUTH。然而，当我运行小程序时，它仍然显示完全一样！

我仔细研究了代码，试图找出我做错了什么，但我完全被难住了。我希望有一双新的眼睛能看到我犯了什么粗心的错误。

欢迎提出任何建议。

Answer 1

你有很多问题...

JPanel 默认使用 FlowLayout，因此由于您从未更改 WholePanel 的布局管理器，因此它一直在使用。

您可能应该将其更改为使用类似 BorderLayout

的内容

public WholePanel() {                            // constructor
    setLayout(new BorderLayout());

现在，基于原来的布局，我可能会想使用 GridBagLayout 作为 subPanel

subPanel.setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
gbc.gridx = 0;
gbc.gridy = 0;
gbc.fill = GridBagConstraints.HORIZONTAL;
subPanel.add(upperPanel, gbc);
gbc.gridy = 1;
gbc.weighty = 1;
gbc.anchor = GridBagConstraints.SOUTH;
subPanel.add(lowerPanel, gbc);               // add each panel to the main subPanel
this.add(subPanel);

这可能会导致类似...

Java 小程序布局未按预期显示 o_O

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