Question

本学期我正在上Java课程并正在进行一项带回家的测验。在其中我们创建了一个类似的计算器，它应该看起来像第一个附加的图像

如您所见，基本面板应分为2行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。

对于这个测验，我创建了2个文件，WholePanel.java和LayoutPanel.java。以下是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applet时，它显示为：
如您所见，看起来好像topPanel和lowerPanel都以某种方式都位于子面板的顶行。

为了好奇，我尝试将subPanel更改为BorderLayout，并将topPanel定位到NORTH，将lowerPanel定位到SOUTH。但是，当我运行applet时，它看起来仍然完全一样！

我仔细考虑了代码，试图看看我做错了什么，但我完全被难过了。我希望一双新鲜的眼睛会看到我犯了什么粗心的错误。

欢迎任何和所有建议。

Answer 1

你有一系列问题......

默认情况下，

JPanel使用FlowLayout，因为您永远不会更改WholePanel的布局管理器，这就是它继续使用的内容。

您应该将其更改为使用BorderLayout

之类的内容

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

现在，根据原始布局，我可能会想GridBagLayout

使用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);

可能导致类似......

Java Applet布局不会显示为o_O

1 个答案: