java - Java中的JComboBox，声明错误

Question

我用 Java 得到了下一个简单的程序，我在网上得到了它，因为我正在尝试学习 Java，但不知道如何修复它:

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

        public class java2 extends JPanel {

            public java2 () {
                setLayout(new Gridlayout(2,1));
                JList lista = new JList(java2.ids);
                add(new JScrollpane(lista));
                JComboBox combo=new JComboBox();
                for (int i=0;i<100 ;i++ ) {
                    combo.addItem(Integer.toString(i));
                    add(combo);
                }
            }
        public static void main(String args[]) {
            java1 lista=new Java1();
            JFrame ventana=new JFrame();
            ventana.getContentPane().add(lista,BorderLayout.CENTER);
            ventana.addWindowListener(new WindowAdapter(){public void windowClosing(WindowEvent evt){System.exit(0);}});
            ventana.setSize(200,200);
            ventana.setVisible(true);
        }
        }

每次编译时我都会遇到下一个问题，正如我所说，我是 java 新手，可以说我知道如何修复它们:

java2.java:8: error: cannot find symbol
        setLayout(new Gridlayout(2,1));
                      ^
  symbol:   class Gridlayout
  location: class java2
java2.java:9: error: cannot find symbol
        JList lista = new JList(java2.ids);
                                     ^
  symbol:   variable ids
  location: class java2
java2.java:10: error: cannot find symbol
        add(new JScrollpane(lista));
                ^
  symbol:   class JScrollpane
  location: class java2
java2.java:18: error: cannot find symbol
    java1 lista=new Java1();
    ^
  symbol:   class java1
  location: class java2
java2.java:18: error: cannot find symbol
    java1 lista=new Java1();
                    ^
  symbol:   class Java1
  location: class java2
Note: java2.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
5 errors

Answer 1

试试这个:

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

public class JavaDemo extends JPanel {

  public JavaDemo() {
    setLayout(new GridLayout(2, 1));
    JList lista = new JList(new String[] {"1", "2", "3", "4"});
    add(new JScrollPane(lista));
    JComboBox combo = new JComboBox();
    for (int i = 0; i < 100; i++) {
      combo.addItem(Integer.toString(i));
      add(combo);
    }
  }

  public static void main(String args[]) {
    JavaDemo lista = new JavaDemo();
    JFrame ventana = new JFrame();
    ventana.getContentPane().add(lista, BorderLayout.CENTER);
    ventana.addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent evt) {
        System.exit(0);
      }
    });
    ventana.setSize(200, 200);
    ventana.setVisible(true);
  }
}