JComboBox 如何从两个 JComboBox 计算两个整数，并在单击 JButton 时将结果保存在 JTextfield 中

我有2个JComboBox由数字组成combobox1= 1 to 5 and combobox2= 1 to 6.

当我点击我的JButton，我希望将两个选定的数字相加并显示在Textfield.

除了计算以及如何将结果放入其中之外，我已经有了完整的代码textfield.

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


public class exer1 extends JFrame{

    JFrame form = new JFrame ("haay");
    JButton btn = new JButton ("Compute");
    JTextField txt = new JTextField (10); 
    JComboBox cb1 = new JComboBox();
    JComboBox cb2 = new JComboBox();


public exer1(){

    form.getContentPane().setLayout(null);
    form.setSize (500,550);

    form.getContentPane().add(txt);
    form.getContentPane().add(btn);
    form.getContentPane().add(cb1);
    form.getContentPane().add(cb2);

    cb1.addItem(new Integer(1));
    cb1.addItem(new Integer(2));
    cb1.addItem(new Integer(3));
    cb1.addItem(new Integer(4));
    cb1.addItem(new Integer(5));
    cb2.addItem(new Integer(1));
    cb2.addItem(new Integer(2));
    cb2.addItem(new Integer(3));
    cb2.addItem(new Integer(4));
    cb2.addItem(new Integer(5));
    cb2.addItem(new Integer(6));

    txt.setBounds(150,90,100,30);
    btn.setBounds(40,170,100,40);
    cb1.setBounds(190,140,50,30);
    cb2.setBounds(190,190,50,30);

    btn.addActionListener(new ActionListener(){
            public void actionPerformed (ActionEvent e){


            }
        });



  form.show();

}




    public static void main (String args []){
        exer1 xx = new exer1();

    }

}

请帮忙。

The sscce http://sscce.org/明确提供了作业，但练习的目标却不太明确。有几件事值得注意。

1. GUI 应该构建在事件派发线程 http://download.oracle.com/javase/tutorial/uiswing/concurrency/initial.html.

2. 按照惯例，类名以首字母大写字母开头。

3. 为了可读性，应该考虑冗长的初始化。

4. 添加到每个的对象JComboBox是类的实例Integer http://download.oracle.com/javase/7/docs/api/java/lang/Integer.html，它对数学整数的子集进行建模。注意原因valueOf() http://download.oracle.com/javase/7/docs/api/java/lang/Integer.html#valueOf%28int%29“通常应该优先于构造函数使用。”

5. 无需将任何内容转换为String直到更新显示的时间actionPerformed()。因为getSelectedItem() http://download.oracle.com/javase/7/docs/api/javax/swing/JComboBox.html#getSelectedItem%28%29返回类型的值Object，结果必须转换为Integer;这在本地构建的数据的上下文中是完全安全的。

6. 一旦Integer值已经恢复，很容易获得总和int value.

7. 最终的转换结果为sum to a String http://download.oracle.com/javase/7/docs/api/java/lang/String.html留作练习。暗示：String http://download.oracle.com/javase/7/docs/api/java/lang/String.html有一个合适的方法，其名称现在看起来可能很熟悉。

8. 成为朋友永远不会太早布局管理器的视觉指南 http://download.oracle.com/javase/tutorial/uiswing/layout/visual.html.

修改后的示例：

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

public class Exercise1 extends JFrame {

    JFrame form = new JFrame("Exercise1");
    JButton btn = new JButton("Compute");
    JTextField txt = new JTextField(10);
    JComboBox<Integer> cb1 = new JComboBox<>();
    JComboBox<Integer> cb2 = new JComboBox<>();

    public Exercise1() {
        form.setLayout(new GridLayout(0, 1));
        form.add(txt);
        form.add(btn);
        form.add(cb1);
        form.add(cb2);
        for (int i = 1; i <= 5; i++) {
            cb1.addItem(Integer.valueOf(i));
            cb2.addItem(Integer.valueOf(i));
        }
        cb2.addItem(new Integer(6));
        btn.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                Integer v1 = (Integer) cb1.getSelectedItem();
                Integer v2 = (Integer) cb2.getSelectedItem();
                int sum = v1.intValue() + v2.intValue();
                txt.setText("42"); // really should convert sum to a String
            }
        });

        form.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        form.pack();
        form.setVisible(true);
    }

    public static void main(String args[]) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                Exercise1 exercise1 = new Exercise1();
            }
        });
    }
}

作为参考，Java 7 引入了ComboBoxModel<E> http://download.oracle.com/javase/7/docs/api/javax/swing/ComboBoxModel.html为了安全地改进类型，尽管getSelectedItem()保持向后兼容。