在不使用 lambda 的情况下实现“IntegerMath 加法”和“IntegerMath 减法”？

Question

I'm currently learning the concept of Lambda in java and I have encountered the following code. The IntegerMath addition and IntegerMath subtraction were defined using lambda. However, I was just curious how to implement IntegerMath addition and IntegerMath subtraction without using lambda? It would be great if the suggestion can be accompanied by some code! Thanks in advance for any help!

public class Calculator {

    interface IntegerMath {
        int operation(int a, int b);   
    }

    public int operateBinary(int a, int b, IntegerMath op) {
        return op.operation(a, b);
    }

    public static void main(String... args) {

        Calculator myApp = new Calculator();
        IntegerMath addition = (a, b) -> a + b;
        IntegerMath subtraction = (a, b) -> a - b;
        System.out.println("40 + 2 = " +
            myApp.operateBinary(40, 2, addition));
        System.out.println("20 - 10 = " +
            myApp.operateBinary(20, 10, subtraction));    
    }
}

Answer 1

Your lambdas are functionally equivalent to anonymous classes like,

IntegerMath addition = new IntegerMath() {
    @Override
    public int operation(int a, int b) {
        return a + b;
    }
};
IntegerMath subtraction = new IntegerMath() {
    @Override
    public int operation(int a, int b) {
        return a - b;
    }
};