JTextField setText()

Question

我制作了一个GUI来反转一个输入字符串，我从第一个textfield获取输入，然后使用函数strRev()反转这个字符串，然后尝试在第二个textfield上生成结果。但是在第二个文本框上没有得到任何输出。

package com.awt;

import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.Spring;
import javax.swing.SpringLayout;
import javax.swing.plaf.basic.BasicOptionPaneUI.ButtonActionListener;

import java.awt.FlowLayout;
import java.awt.GridBagLayout;
import java.awt.GridBagConstraints;
import java.awt.Insets;
import java.awt.GridLayout;
import javax.swing.JButton;
import javax.swing.JTextField;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.event.InputMethodListener;
import java.awt.event.InputMethodEvent;

public class Buttons{

    private JFrame frame;
    private JTextField textField;
    private JTextField textField_1;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    Buttons window = new Buttons();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }
    
    public Buttons() {
        initialize();
    }
    
    public String strRev(String s) {
        char a;
        String ans="";
        for(int i=0;i<s.length();i++) {
            a=s.charAt(i);
            ans=a+ans;
        }
        return ans;
    }

    private void initialize() {
        frame = new JFrame("Label Demo");
        frame.setBounds(150, 200, 450, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(new FlowLayout(FlowLayout.CENTER, 5, 5));
        
        textField = new JTextField();
        frame.getContentPane().add(textField);
        textField.setColumns(10);
        
        JButton okButton = new JButton("Reverse");
        frame.getContentPane().add(okButton);
        
        textField_1 = new JTextField();
        frame.getContentPane().add(textField_1);
        textField_1.setColumns(10);
        
        String str=textField.getText();
        final String ans=strRev(str);
        
        okButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                textField_1.setText(ans);
            }
        });
        
    }

}

GUI如下所示：-

​

请告诉我我的错误，谢谢

Answer 1

只有当用户单击反向按钮时，才需要读取textField的内容。目前，当GUI加载时，当textField中没有任何内容时，您将读取内容。因此，对空字符串进行反向调用将给您提供一个空字符串，这就是您在textField_1中看到的。将读取textField的代码移动到addActionListener中。

private void initialize() {
    frame = new JFrame("Label Demo");
    frame.setBounds(150, 200, 450, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().setLayout(new FlowLayout(FlowLayout.CENTER, 5, 5));
    
    textField = new JTextField();
    frame.getContentPane().add(textField);
    textField.setColumns(10);
    
    JButton okButton = new JButton("Reverse");
    frame.getContentPane().add(okButton);
    
    textField_1 = new JTextField();
    frame.getContentPane().add(textField_1);
    textField_1.setColumns(10);
    
    okButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            // THIS BLOCK IS RUN EVERYTIME THE BUTTON IS CLICKED!
            // Read the contents of textField
            String str=textField.getText();
            // Reverse the string you just read
            final String ans=strRev(str);
            // Set the answer on the other textField.
            textField_1.setText(ans);
        }
    });   
}