程序填空：分析代码将程序补充完整，实现计算器功能，能正常完成加减乘除运算。 _____(1)______ Computer { int computer(int n, int m); } class Add ________(2)___________ { public int computer(int n, int m) { System.out.print(n+"+"+m+"="); return n+m; } } class Sub implements Computer { public int computer (int n, int m) { ______________(3)_________________ return n-m; } } class Mul implements Computer { public int computer (int n, int m) { System.out.print(n+"*"+m+"="); return n*m; } } class Div implements Computer { public int computer (int n, int m) { System.out.print(n+"/"+m+"="); return n/m； } } class UseComputer { public void useCom(Computer com, int one, int two) { System.out.println (____________(4)______________); } } public class Test { public static void main (String[] args) { _______________(5)______________________ uc.useCom(new Add(), 10, 20); uc.useCom(new Sub(), 15, 10); uc.useCom(new Mul(), 10, 20); uc.useCom(new Div(), 15, 5); } }

代码如下：

(1) interface
Computer {
    int computer(int n, int m);
}

class Add implements Computer {
    public int computer(int n, int m) {
        System.out.print(n + "+" + m + "=");
        return n + m;
    }
}

class Sub implements Computer {
    public int computer(int n, int m) {
        System.out.print(n + "-" + m + "=");
        return n - m;
    }
}

class Mul implements Computer {
    public int computer(int n, int m) {
        System.out.print(n + "*" + m + "=");
        return n * m;
    }
}

class Div implements Computer {
    public int computer(int n, int m) {
        System.out.print(n + "/" + m + "=");
        return n / m;
    }
}

class UseComputer {
    public void useCom(Computer com, int one, int two) {
        System.out.println(com.computer(one, two));
    }
}

public class Test {
    public static void main(String[] args) {
        UseComputer uc = new UseComputer();
        uc.useCom(new Add(), 10, 20);
        uc.useCom(new Sub(), 15, 10);
        uc.useCom(new Mul(), 10, 20);
        uc.useCom(new Div(), 15, 5);
    }
}