程序代码：

package thread_437601;

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

public class GetTextTest {
    
    public static void main(String args[]) {
        MyFrame myframe = new MyFrame();
    }
}

class MyFrame extends JFrame {

    public MyFrame() {
        this.getContentPane().setLayout(null);
        jtextfield.setBounds(10, 10, 100, 20);
        jbutton.setBounds(10, 40, 100, 20);
        jbutton.addActionListener((ActionEvent e) -> {
            String jtextfield_text = jtextfield.getText();
            if ("".equals(jtextfield_text)) {
                JOptionPane.showMessageDialog(null, "2楼说的对", "无输入内容时getText()取得值", JOptionPane.PLAIN_MESSAGE);
            } else if (null == jtextfield_text) {
                JOptionPane.showMessageDialog(null, "3楼说的对", "无输入内容时getText()取得值", JOptionPane.PLAIN_MESSAGE);
            } else {
                JOptionPane.showMessageDialog(null, "2楼和3楼都不对", "无输入内容时getText()取得值", JOptionPane.PLAIN_MESSAGE);
            }
        });
        this.getContentPane().add(jtextfield);
        this.getContentPane().add(jbutton);
        this.setSize(120, 120);
        this.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        this.setVisible(true);
    }
    private JTextField jtextfield = new JTextField();
    private final JButton jbutton = new JButton("Button");
}