Question

我有两个JComboBox由数字combobox1= 1 to 5和c ombobox2= 1 to 6.

组成

当我点击我的JButton时，我希望添加两个所选数字并显示在Textfield.

上

我已经有完整的代码，除了计算以及如何在textfield.

中得到结果

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。

Answer 1

提供的sscce显然是家庭作业，但练习的目标并不那么明确。有些事情值得注意。

应在event dispatch thread。
按照惯例，类名以首字母大写字母开头。
为了便于阅读，应考虑冗长的初始化。
添加到每个JComboBox的对象是类Integer的实例，它为数学整数的子集建模。注意为什么valueOf()“通常应该优先于构造函数使用。”
在更新String中的显示之前，无需将任何内容转换为actionPerformed()。由于getSelectedItem()返回Object类型的值，因此结果必须转换为Integer;这在本地构建的数据中非常安全。
恢复Integer值后，很容易将总和作为int值。
sum到String的最终转换仅作为练习。提示：String有一个合适的方法，其名称现在看起来很熟悉。
与A Visual Guide to Layout Managers成为朋友永远不会太早。

修订示例：

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ComboBoxModel<E>以安全地改进类型，尽管getSelectedItem()仍向后兼容。

Answer 2

我有点改写了整个剧本（抱歉给您带来任何不便）......

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

public class exer1 extends JFrame implements ActionListener {
    JPanel row1 = new JPanel();
    JLabel first = new JLabel("Select the first number:", JLabel.RIGHT);
    JComboBox fNum = new JComboBox();
    JPanel row2 = new JPanel();
    JLabel second = new JLabel("Select the second number:", JLabel.RIGHT);
    JComboBox sNum = new JComboBox();
    JPanel row3 = new JPanel();
    JButton comp = new JButton("Compute");
    JTextField total = new JTextField(5);

    public exer1() {
        super("Calculator");
        row1.add(first);
        fNum.addItem("1");
        fNum.addItem("2");
        fNum.addItem("3");
        fNum.addItem("4");
        fNum.addItem("5");
        fNum.addItem("6");
        row1.add(fNum);
        add(row1);
        row2.add(second);
        sNum.addItem("1");
        sNum.addItem("2");
        sNum.addItem("3");
        sNum.addItem("4");
        sNum.addItem("5");
        sNum.addItem("6");
        row2.add(sNum);
        add(row2);
        comp.addActionListener(this);
        row3.add(comp);
        total.setEditable(false);
        row3.add(total);
        add(row3);
        setLayout(new FlowLayout());
        setSize(500, 550);
        setVisible(true);
    }

    public void actionPerformed(ActionEvent event) {
        int num1 = Integer.parseInt(fNum.getSelectedItem().toString());
        int num2 = Integer.parseInt(sNum.getSelectedItem().toString());
        total.setText("" + (num1 + num2));
    }

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

Answer 3

使用form.setVisible(true);

然后：

    btn.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {
            int cb1Int = Integer.parseInt(cb1.getSelectedItem().toString());
            int cb2Int = Integer.parseInt(cb2.getSelectedItem().toString());
            txt.setText(String.valueOf(cb1Int + cb2Int));
        }
    });

祝你好作业。 ;）

JComboBox如何计算来自两个JComboBox的两个整数，并在单击JButton时将结果放在JTextfield中

3 个答案: