通过 JButton 从 JTextField 获取字符串

Question

我正在编写一个程序，我几乎完成了。我想要的是：在 JTextField 中输入一个字符串，按下一个 JButton，我希望字符串出现在另一个 JTextField 中。所以我有：2 个 JTextField 和 1 个按钮。这是我的代码：

class Fenster extends JFrame {
JTextField inputfield;
JTextField outputfield;
JButton button;
public Fenster() {

    JTextField outputfield = new JTextField();
    outputfield.setBounds(50, 315, 400, 32);
    add(outputfield);

JTextField inputfield = new JTextField();
    inputfield.setBounds(50, 115, 400, 32);
    add(inputfield);
//The Button
JButton button = new JButton("Klick me :D");
    button.setBounds(154, 250, 92, 32);
    button.addActionListener(new buttonlistener());
    add(button);

private class buttonlistener implements ActionListener {

    public void actionPerformed(ActionEvent e) {
String string = inputfield.getText();
outputfield.setText(string);

}
}
}

我知道我没有包含 JFrame 设置。请帮忙，因为每次我按下按钮时都会出现错误：“buttonlistener.actionPerformed(Fenster.java:70)”出现：S

提前致谢

Answer 1

字段outputfield 和inputfield 被声明为Fenster 类的属性和Fenster 构造函数的局部变量。

我们在面板上看到的是本地声明的，但是动作监听器试图使用声明为从未初始化的类属性的那些。因此NullPointerException。

Answer 2

您可以在初始化ActionListener 时直接实现它，而不是为其创建单独的函数。

//The Button
JButton button = new JButton("Klick me :D");
button.setBounds(154, 250, 92, 32);
button.addActionListener(new ActionListener(){
    @Override
    public void actionPerformed(ActionEvent e) {
        String string = inputfield.getText();
        outputfield.setText(string);
    }
});
add(button);

Answer 3

我无法准确解读您的要求。所以我只是假设你的要求

---

“如何让我的字符串输出到 JButton？”

我将给你我曾经这样做的代码。现在，我创建了一个字符串值，您就可以开始编码了！：

import java.util.*;
import java.awt.*;
import javax.swing.*;
import java.lang.Object;
import java.io.*;
import javax.imageio.*;

public class jframetest extends Object
{
    public static void main(String args[]) throws Exception  
    {

        JFrame frame = new JFrame("Not Main");

                        /* Background Image*/
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 *       JLabel image = new JLabel(new ImageIcon("a.jpg"));        *
 *       image.setBounds(0,0, 800, 600);                           *
 *       frame.getContentPane().add(image, BorderLayout.CENTER);   *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

        Random generate = new Random();
        Random rand = new Random();

        String[] name =    {"Landry", "Azariah", "Oakley", "Lennon", "Charlie", "Skyler", "Dakota", "Armani", "Phoenix" , "Justice", "Casey", "Emory", "Remy", "Emerson", "Amari", "Roxie", "Hayden", "River", "Milan", "Tatum", "Jessie", "Finley", "Riley", "Rowan", "Sage", "Jamie", "Rory", "Harley", "Leighton", "Peyton", "Dallas", "Remington", "Quinn", "Alexis", "Sawyer", "Kamryn", "Parker", "Avery", "Eden", "Lyric", "Elliot", "Reese", "Zion", "Rylan", "Jordan", "Taylor", "Morgan", "Kendall", "Rylee", "Ryan", "Reagan", "Logan", "Hunter", "Carter"};


  int index = (int) (Math.random() * (name.length - 1));

  JButton buttun = new JButton(name[index]);
  buttun.setBounds(190,65,400,50);

  JLabel label2 = new JLabel("Customer: " + name[generate.nextInt(20)]);
  label2.setBounds(190,65,400,50); //setBounds(x,y,width,height);
  label2.setFont(new Font("Serif", Font.BOLD, 40));



  frame.setPreferredSize(new Dimension(200, 200));     
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  //frame.getContentPane().add(button); (not needed when Background Image is commented) 
  frame.setVisible(true);
  frame.pack();
  frame.add(buttun);
  frame.add(label2);   
  frame.setSize(800, 600);
  frame.setLayout(null);

   }
}