How to implement lazy evaluation in java

Explanation

1. Lazy evaluation is the process of delaying the evaluation of an expression until needed. Java is strictly immediate assignment evaluation.

2. It can be rewritten into a lazy-evaluated version using lambda expressions and higher-order functions.

Example

public class LazySample {
    public static void main(String[] args) {
        //这是一个lambda表达式，表现为闭包
        UnaryOperator<Integer> add = t -> {
            System.out.println("executing add");
            return t + t;
        };
      //这是一个lambda表达式，表现为闭包
        UnaryOperator<Integer> multiply = t -> {
            System.out.println("executing multiply");
            return t * t;
        };
        //传递Lambda闭包而不是普通函数
        System.out.println(addOrMultiply(true, add, multiply, 4));
        System.out.println(addOrMultiply(false, add, multiply, 4));
    }
 
    //这是一个高阶函数
    static <T, R> R addOrMultiply(
            boolean add, Function<T, R> onAdd,
            Function<T, R> onMultiply, T t
    ) {
        // Java的？会懒惰计算表达式，因此仅执行所需的方法
        return (add ? onAdd.apply(t) : onMultiply.apply(t));
    }
}

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