Java8 Effectively Final compile time error on non

问题:

I'm trying to change the boolean variable inside java8 forEach loop to true which is non final. But I'm getting following error : Local variable required defined in an enclosing scope must be final or effectively final.

How to resolve this error?

Code :

boolean required = false; 

This is the variable I have created in the function.

Now when I'm trying to change it :

   map.forEach((key, value) -> {
        System.out.println("Key : " + key + " Value : " + value);
        required = true;
    });

I'm getting the error : Local variable required defined in an enclosing scope must be final or effectively final.

Why this error is arising and how to resolve it?

回答1:

You cannot change the local variable from the body of lambda expression. There are several ways to overcome this:

• In this particular case you can just set boolean required = !map.isEmpty(); without any lambda expression. If you want to set it based on some condition, you can use the Stream API:

  boolean required = map.entrySet().stream().anyMatch(entry -> ...);
  

  This solution is the most preferred.

• Convert the required variable to the field of the enclosing class.

• The most dirty way: declare a one-element array: boolean[] required = {false}; and set this element instead: required[0] = true;