Java8: Closures

In the below code Calculator class implementation will have access to b variable even its not in the scope. This is done by java compiler having a copy of b variable and sending to the calculator class.

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int a=10;
int b=20;
operate(a, new Calculator() {
    @Override
    public void process(int i) {
        System.out.println(i + " - " + b);
    }
});

What if you try change this value of be

int a=10;
int b=20;
operate(a, new Calculator() {
    b=2;
    @Override
    public void process(int i) {
        System.out.println(i + " - " + b);
    }
});

You will get the following error.

Variable used in lambda expression should be final or effectively final

Before Java 8 you must declare the variable b as a final and from java 8 you can use it without changing the variable. If you try to change you will see above error.

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