Java GUI 按钮不会将字符串打印到界面

Question

GUI 初学者在这里。

我的问题不是创建 GUI 界面，而是让 2 个按钮在界面内的 JTextArea 中打印字符串。
第一个“已学习”按钮从数组中获取随机元素并打印它。第二个按钮“清除”应该在按下时打印一个字符串我有两个按钮的 Action 监听器，但仍然无法完全理解它。

感谢您的宝贵时间。

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.Random;


public class GUI extends JFrame {


String [] sentences = {"Random sentence 1", "random sentence 2", "random sentence 3", "random sentence 4", random sentence 5", "random sentence 6"};


private Container contents;
JButton learned = new JButton("Learned");
JButton clear = new JButton("Clear");
JTextArea clearDisplay;


public GUI()
{
    super ("GUI"); //title bar text

    contents = getContentPane ();
    contents.setLayout(new FlowLayout()); //make buttons appear

    //set the layout manager

    //instantiate buttons
    learned = new JButton("I Learned");
    clear = new JButton("Clear");

    //add components to window
    contents.add(learned);
    contents.add(clear);



    //instantiate event handler
    ButtonHandler bh = new ButtonHandler ();

    //add event handler as listener for both buttons
    learned.addActionListener (bh);
    clear.addActionListener(bh);

    setSize (400, 200); //size of window
    setVisible (true); //see the window

    }


   public class ButtonHandler implements ActionListener
   {
    //implement ActionPerformed method

    public void actionPerformed(ActionEvent e)
    {
        Container contentPane = getContentPane();
       if (e.getSource() == learned)
       {
         String random = (sentances[new Random().nextInt(sentances.length)]); //random from array           
         JTextArea learned = new JTextArea(random);
       }
       else if (e.getSource() == clear)           
       {
            JTextArea clearDisplay = new JTextArea("This is where it will display what I learned. \\nMessage Displayed Here.");
       }

    }

}

public static void main(String[] args)
{  
   GUI basicGui = new GUI (); 
   basicGui.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //program exits on close                              
}

}

Answer 1

您的问题在这里:

else if (e.getSource() == clear)           
   {
        JTextArea clearDisplay = new JTextArea("This is where it will display what I learned. \\nMessage Displayed Here.");
   }

您正在创建一个永远不会添加到 GUI 的新 JTextArea。你应该这样写:

else if (e.getSource() == clear)           
   {
        clearDisplay = new JTextArea("This is where it will display what I learned. \\nMessage Displayed Here.");
   }

并将其添加到 GUI。

您还应该考虑一种不同的方法:首先创建 JTextField，将其添加到 GUI，然后仅更改上面代码中的文本。

此外，您这里还有一些拼写错误:

String random = (sentances[new Random().nextInt(sentances.length)]);