Question

我可以运行此applet，但它不会显示任何JApplet组件，applet不会显示标签或文本字段，希望我的if / else状态是正确的。

package JavaPractice;

/* Dominic Spucches
Exercise 7-2
This program will compare 2 applets
*/

import java.awt.*;
import java.awt.event.AWTEventListener;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

public abstract class ex7_2 extends JApplet implements ActionListener {

    private static final long serialVersionUID = 1L;
        JLabel st1 = new JLabel("Enter a string: ");
        JTextField str1 = new JTextField();
        JLabel st2 = new JLabel("Enter a string: ");
        JTextField str2 = new JTextField();
        JLabel same1 = new JLabel();
        JLabel same2 = new JLabel();
        JLabel results = new JLabel();
        FlowLayout flow = new FlowLayout();
        Container c;


    public void init()
    {

        c = getContentPane();
        c.setLayout(flow);
        c.setBackground(Color.gray);
        st1.setForeground(Color.blue);
        c.add(st1);
        str1.setForeground(Color.blue);
        c.add(str1);
        st2.setForeground(Color.blue);
        c.add(st2);
        str2.setForeground(Color.blue);
        c.add(str2);
        str2.addActionListener(this);       
        same1.setForeground(Color.blue);
        c.add(same1);       
        same2.setForeground(Color.blue);
        c.add(same2);
        results.setForeground(Color.blue);
        c.add(results);




    }

    public void actionPerformed(ActionEvent e)
    {
        String str1, str2;

        if (str1.equals(str2))  // s1 == s2
            same1.setText("Same string");
        else if (str1.equalsIgnoreCase(str2))
            same2.setText("Same string - different case");
        else if (str1.compareTo(str2) > 0)  // s1 > s2
            results.setText(str1 + " is alphabetically greater than "
                    + str2);
        else        // s1 < s2
            results.setText(str1 + " is alphabetically less than "
                    + str2);
        results.setText("Difference is " + (str1.compareTo(str2)) /*i keep getting an error here as well in eclipse, no clue */
    }

}

Answer 1

从类声明中删除abstract关键字，以便可以实例化

public abstract class ex7_2 extends JApplet implements ActionListener {
       ^

Answer 2

你的例子有几个观察结果：

如图here所示，abstract类无法直接实例化。
在actionPerformed()中，应将本地字符串设置为相应的文本字段值。
请注意下面actionPerformed()中的修订逻辑。
您的上一个错误源于缺少分号。
请注意使用组件初始化来建立初始大小。
考虑今后审核的相关小程序问题here。
另请参阅Initial Threads。

//<applet code="ex7_2.class" width=500 height=100></applet>
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

public class ex7_2 extends JApplet implements ActionListener {

    JLabel st1 = new JLabel("Enter a string: ");
    JTextField str1 = new JTextField(8);
    JLabel st2 = new JLabel("Enter a string: ");
    JTextField str2 = new JTextField(8);
    JLabel equals =  new JLabel("        ");
    JLabel compare = new JLabel("        ");
    JLabel results = new JLabel("        ");
    FlowLayout flow = new FlowLayout(FlowLayout.LEFT, 8, 8);

    @Override
    public void init() {
        Container c = getContentPane();
        c.setLayout(flow);
        c.setBackground(Color.lightGray);
        st1.setForeground(Color.blue);
        c.add(st1);
        str1.setForeground(Color.blue);
        c.add(str1);
        st2.setForeground(Color.blue);
        c.add(st2);
        str2.setForeground(Color.blue);
        c.add(str2);
        str2.addActionListener(this);
        equals.setForeground(Color.blue);
        c.add(equals);
        compare.setForeground(Color.blue);
        c.add(compare);
        results.setForeground(Color.blue);
        c.add(results);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        String s1 = str1.getText();
        String s2 = str2.getText();
        if (s1.equals(s2)) {
            equals.setText("Same strings.");
        } else if (s1.equalsIgnoreCase(s2)) {
            equals.setText("Same strings, different case.");
        } else {
            equals.setText("Different strings.");
        }
        if (s1.compareTo(s2) > 0) {
            compare.setText(s1 + " is alphabetically greater than " + s2 + ".");
        } else {
            compare.setText(s1 + " is alphabetically less than " + s2 + ".");
        }
        results.setText("Difference is " + (s1.compareTo(s2) + "."));
    }
}

遇到这个JApplet的问题，不确定它为什么不起作用

2 个答案: