java 编写一个类，定义3个静态重载方法，分别用于求两整效的和、两浮点数的和以及两字符串的连接。并编写该类的测试程序。

public class Calculator {
    public static int add(int a, int b) {
        return a + b;
    }

    public static double add(double a, double b) {
        return a + b;
    }

    public static String add(String a, String b) {
        return a + b;
    }

    public static void main(String[] args) {
        int result1 = Calculator.add(3, 4);
        double result2 = Calculator.add(3.5, 4.5);
        String result3 = Calculator.add("Hello", "World");
        System.out.println("result1: " + result1);
        System.out.println("result2: " + result2);
        System.out.println("result3: " + result3);
    }
}

输出结果：

result1: 7
result2: 8.0
result3: HelloWorld