Question

感谢您的帮助......现在该程序可以正常运行并运行...但我还有2个问题。 1.如何将输出输出到JTestField t4或t5 2.如何使用JButton Buton3

关闭应用程序

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
import javax.swing.JButton;
import javax.swing.JFrame;
public class TriangleFarfan{
JFrame Triangle = new JFrame("Triangle Calculator");
   JButton Button1 = new JButton ("Area");
   JButton Button2 = new JButton("Perimeter");
   JButton Button3 = new JButton("Close");
   JTextField t1 = new JTextField(20);
   String t1TextBox = t1.getText();
   double side1 = Double.parseDouble(t1TextBox);
   JPanel j1 = new JPanel (new FlowLayout());
   JLabel l1 = new JLabel("Enter side 1:");
   JTextField t2 = new JTextField();
   String t2TextBox = t2.getText();
   double side2 = Double.parseDouble(t2TextBox);
   JPanel j2 = new JPanel (new FlowLayout());
   JLabel l2 = new JLabel("Enter side 2:");
   JTextField t3 = new JTextField();
   String t3TextBox = t3.getText();
   double side3 = Double.parseDouble(t3TextBox);
   JPanel j3 = new JPanel (new FlowLayout());
   JLabel l3 = new JLabel("Enter side 3:");
   JTextField t4 = new JTextField();
   JPanel j4 = new JPanel (new FlowLayout());
   JLabel l4 = new JLabel("Area Result");
   JTextField t5 = new JTextField(20);
   JPanel j5 = new JPanel (new FlowLayout());
   JLabel l5 = new JLabel("Perimeter Result");
public TriangleFarfan()
    {
    j1.add(l1);
    j1.add(t1);
    j2.add(l2);
    j2.add(t2);
    j3.add(l3);
    j3.add(t3);
    j4.add(l4);
    j4.add(t4);
    j5.add(l5);
    j5.add(t5);
    Triangle.add(j1);
    Triangle.add(j2);
    Triangle.add(j3);
    Triangle.add(j4);
    Triangle.add(j5);
    Triangle.add(Button1);
    Button1.addActionListener(new ActionListener() {

           public void actionPerformed(ActionEvent e)
           {
               double Area = (side1 * side2)/2;
               //Execute when button is pressed
               System.out.println(Area);
           }
       });      
    Triangle.add(Button2);
    Button2.addActionListener(new ActionListener() {

           public void actionPerformed(ActionEvent e)
           {
               //Execute when button is pressed
               System.out.println("You clicked the Perimeter Button");
           }
       });      
    Triangle.add(Button3);
    Button3.addActionListener(new ActionListener() {

           public void actionPerformed(ActionEvent e)
           {
               //Execute when button is pressed
               System.out.println("You clicked the Close Button");
           }
       });      
    Triangle.setLayout(new FlowLayout());
    Triangle.setSize(450,400);
    Triangle.setVisible(true);
    Triangle.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

  }

}

Answer 1

除了缺少主要方法，正如Reimeus指出的那样，你的指示顺序是错误的。在屏幕上显示任何内容之前，甚至在创建对象之前，您都试图读取用户输入。例如，这一行：

String t1TextBox = t1.getText();

尝试从TextBox中获取一个文本，该文本甚至没有添加到尚未创建的Panel中。

要解决此问题，您需要重新考虑程序的逻辑。以下是一些提示：

避免在方法之外进行分配。而不是写
```
JFrame Triangle = new JFrame("Triangle Calculator");
```
在类体中声明变量，如下所示：
```
JFrame Triangle;
```
并将其分配到构造函数中，如下所示：
```
Triangle = new JFrame("Triangle Calculator");
```
构建整个UI，然后担心听众。这样，您可以确保在获取用户输入时不引用不存在的UI元素。

在侦听器中获取用户输入，如下所示：

 Button1.addActionListener(new ActionListener() {

   public void actionPerformed(ActionEvent e)
   {
       // get the size of side1 from the textbox
       String t1TextBox = t1.getText();
       double side1 = Double.parseDouble(t1TextBox);

       // get the size of side2 from the textbox
       String t2TextBox = t2.getText();
       double side2 = Double.parseDouble(t2TextBox);

       // now we can calculate the area
       double Area = (side1 * side2)/2;

       //Execute when button is pressed
       System.out.println(Area);
   }

}）;

Answer 2

添加main方法：

public static void main(String[] args) {
   SwingUtilities.invokeLater(new Runnable() {
      @Override
      public void run() {
         new TriangleFarfan();
      }
   });
}

声明

JTextField t1 = new JTextField(20);

未将JTextField中的值设置为20。相反，它会为JTextComponent设置列数，但为空String。因此行

double side1 = Double.parseDouble(t1TextBox);

将在启动时抛出NumberFormatException。

使用JTextField进行用户输入

2 个答案: