Capturing lambdas

A lambda expression is said to be capturing if it either accesses instance variables of it’s enclosing class or local variables (final or effectively final) from it’s enclosing scope.

A lambda expression can capture the three types of variables given below:

• Static variables
• Instance variables
• Local variables

If a lambda expression captures a local variable then the variable should be either final or effectively final.

What is effectively final?

Effectively final is a new concept that was introduced in Java 8. A non-final, local variable whose value is never changed after initialization is known as effectively final.

Before Java 8, we cannot use a non-final, local variable in an anonymous class. If you need to access a local variable in an anonymous class, then it should be declared as final. This restriction is relaxed in Java 8. Now, the compiler, itself can check if the value of a variable is not changed after the assignment. Then, it is effectively final.