代码如下：

import java.awt.Graphics;
import javax.swing.*;
//*********Found********** 
public class Java_3 extends ____________________ {
 
    double sum; //存和的变量 
    //*********Found********** 
    public void __________________() {
        String firstNumber, //输入第1个字符串格式的数 
                secondNumber; //输入第2个字符串格式的数 
        double number1, //加数 
                number2; //被加数 
        //读入第1个输入的数 
        firstNumber =
                JOptionPane.showInputDialog(
                "Enter first floating-point value");
        //读入第2个输入的数 
        secondNumber =
                JOptionPane.showInputDialog(
                "Enter second floating-point value");
        //将字符串数据转换成双字长类型 
        number1 = Double.parseDouble(firstNumber);
        number2 = Double.parseDouble(secondNumber);
        //数据相加 
        sum = number1 + number2;
    }
 
    public void paint(Graphics g) {
        //用g.drawString给结果 
        g.drawRect(15, 10, 270, 20);
        g.drawString("数相加之和为:" + sum, 25, 25);
    }
}