有什么办法可以改变Java Lambda捕获的价值 [英] Is there any way to change value captured by Java Lambda

问题描述

类似的东西:

    Integer value = 3;
    Consumer<Integer> consumer = input -> {
        value = value * 2;
    };
    consumer.accept(100);
    System.out.println(value);

谢谢！ [已解决]

    AtomicInteger value = new AtomicInteger(3);
    Consumer<Integer> consumer = input -> {
        value.getAndAdd(5); // 8
        System.out.println(value.get());
    };
    consumer.accept(100);
    System.out.println(value.get()); // 8

也感谢Umer Farooq的回答 从lambda内部修改局部变量

also thanks for Umer Farooq` s answer Modifying local variable from inside lambda

推荐答案

不，那不可能.

JLS 15.27. 2 说:

使用但未在lambda表达式中声明的任何局部变量，形式参数或异常参数必须声明为final或有效地为final(第4.12.4节)，否则在尝试使用时会发生编译时错误.

Any local variable, formal parameter, or exception parameter used but not declared in a lambda expression must either be declared final or be effectively final (§4.12.4), or a compile-time error occurs where the use is attempted.

由于在lambda中使用了value，但在lambda之外声明了它，因此它必须是final或有效的final.这意味着您不能多次为其分配一个值.

Since you use value in the lambda, but declare it outside of the lambda, it has to be final or effectively final. That means you can't assign it a value more than once.

当然，如果value是可变对象(例如，AtomicInteger)，那么您将能够对其进行突变. value引用本身将保持不变，但引用的对象将被更改.

Of course, if value were a mutable object (an AtomicInteger, for instance), then you would be able to mutate it. The value reference itself would be unchanged, but the object it references would be changed.

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