写个控制台的小程序你看看吧, 实现了double数据类型的加减乘除

 import java.util.Scanner;

public class Calc {
    private static int operatorId;  //记录选择的运算方式
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("输入第一个数字：");
        double num1 = sc.nextDouble();
        System.out.println("输入第二个数字：");
        double num2 = sc.nextDouble();
        System.out.println("选择运算方式：");
        System.out.println("1. 加法");
        System.out.println("2. 减法");
        System.out.println("3. 乘法");
        System.out.println("4. 除法");
        System.out.print("输入编号：");
        operatorId = sc.nextInt();
        double res = calcMethod(num1, num2);
        System.out.println("计算结果：" + res);
        sc.close();
    }
    /**
     * 两个double数计算方法
     * @param num1
     * @param num2
     * @return 计算结果
     */
    private static double calcMethod(double num1, double num2) {
        double res = 0.0;
        switch (operatorId) {
        case 1:
            res = num1 + num2;
            break;
        case 2:
            res = num1 - num2;
            break;
        case 3:
            res = num1 * num2;
            break;
        case 4:
            res = num1 / num2;
            break;
        }
        return res;
    }
}

一样的问题，自己看

http://zhidao.baidu.com/link?url=ftir0N2JIJDLDexgrb-8hWOHE_NgNxlcP446siOLLZqUT7nwBrREY6KDrDcNEjVE1yqQZYLERnp0LrdkeTecS_

http://wenda.haosou.com/q/1370292592070767

http://zhidao.baidu.com/question/1366043443705251419.html

http://wenda.haosou.com/q/1367448512061264

http://zhidao.baidu.com/question/346981477.html

http://download.csdn.net/detail/WW_LC/1992048

http://download.csdn.net/download/QQ839586169/2733193

这样的例子程序能找到很多，随便找一个参考下。