ex6

ゞ浴缸里的玫瑰 2022-08-04 12:36 129阅读 0赞

import java.awt.FlowLayout;
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    import java.util.regex.Matcher;
    import java.util.regex.Pattern;
    
    import javax.swing.JButton;
    import javax.swing.JFrame;
    import javax.swing.JTextArea;
    import javax.swing.JTextField;
    
    import static net.mindview.util.SwingConsole.*;
    
    public class ex06 extends JFrame { 
    
        JTextArea text1 = new JTextArea(20,40);
        JTextArea text2 = new JTextArea(20,40);
        JTextField txt = new JTextField(20);
        JButton bn = new JButton("button");
    
        public ex06() {
            bn.addActionListener(new ActionListener() {
    
                @Override
                public void actionPerformed(ActionEvent e) {
    
                    if (text1.getText() == "") {
                        text2.append("Usage:\njava TestRegularExpression "
                                + "characterSequence regularExpression+"+"\n");
                        return;
                    }
                    text2.append("Input: \"" + text1.getText() + "\""+"\n");
                    String arg = txt.getText();
                    text2.append("Regular expression: \"" + arg + "\""+"\n");
                    Pattern p = Pattern.compile(arg);
                    Matcher m = p.matcher(text1.getText());
                    while (m.find()) {
                        text2.append("Match \"" + m.group()
                                + "\" at positions " + m.start() + "-"
                                + (m.end() - 1)+"\n");
                    }
    
                }
            });
    
            setLayout(new FlowLayout());
            add(text1);
            add(txt);
            add(bn);
            add(text2);
        }
    
        public static void main(String[]args){
            run(new ex06(),800,400);
        }
    }

当`JTextArea`是空时，`getText()`返回的好像既不是`null`也不是`""`  
不知具体返回的是什么