java - 如何使用 JTextField 在 JTextField 本身上使用 ActionListener 显示否定或肯定结果

Question

我的程序应该要求用户在 JTextField 中写入一个数字，然后在另一个禁用的 JTextField 中显示该数字为负数或正数的结果。所有这些都必须在没有按钮的情况下完成。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
  
public class PositiveOrNegative extends JFrame { 
    JLabel l1, l2 ;
    JTextField t1, t2 ;

    public PositiveOrNegative() 
    {
        FlowLayout layout = new FlowLayout(); 
        this.setLayout(layout); 

        l1 = new JLabel("Enter a number "); 
        t1 = new JTextField(10) ;
        l2 = new JLabel("The number is  ");
        t2 = new JTextField(10) ;

        this.add(l1); 
        this.add(t1);
        this.add(l2);
        this.add(t2);
        t2.enable(false);
        t2.setBackground(Color.PINK);
    }

    public void JavaJTextFieldActionListner() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        t1.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                String n = t1.getText() ;
                int number = Integer.parseInt(n) ;
                if (number >= 0)
                    t2.setText("POSITIVE") ;
                else
                    t2.setText("NEGATIVE") ;
            }
        });
    }

    public static void main(String[] args) {
        PositiveOrNegative p = new PositiveOrNegative(); 
        p.setTitle("AWT SIGN"); 
        p.setBounds(300, 300, 300, 120); 
        p.setVisible(true); 
    } 
} 

Answer 1

在您的示例中，您忘记调用方法JavaJTextFieldActionListner。我已将其删除并将代码移至构造函数中。我还添加了对错误输入的处理。结果如下:

import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField; 

public class PositiveOrNegative extends JFrame {

    JLabel l1, l2 ;
    JTextField t1, t2 ;

    public PositiveOrNegative() {
        FlowLayout layout = new FlowLayout(); 

        this.setLayout(layout); 

        l1 = new JLabel("Enter a number "); 
        t1 = new JTextField(10);
        l2 = new JLabel("The number is  ");
        t2 = new JTextField(10);

        this.add(l1); 
        this.add(t1);
        this.add(l2);
        this.add(t2);
        t2.setEditable(false);
        t2.setBackground(Color.PINK);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        t1.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                String n = t1.getText();
                try {
                    int number = Integer.parseInt(n);

                    if (number >= 0)
                        t2.setText("POSITIVE");
                    else
                        t2.setText("NEGATIVE");
                } catch (Exception ex) {
                    t2.setText("Not an integer");
                }
            }
        });
    }

    public static void main(String[] args) { 
        PositiveOrNegative p = new PositiveOrNegative(); 
        p.setTitle("AWT SIGN"); 
        p.setBounds(300, 300, 300, 120); 
        p.setVisible(true); 
    } 

}