The documentation on Anonymous Classes states
An anonymous class cannot access local variables in its enclosing scope that are not declared as final or effectively final.
I don't understand what does a variable being "effective final" mean. Can someone provide an example to help me understand what that means?
Effectively final means that it is never changed after getting the initial value.
A simple example:
public void myMethod() {
int a = 1;
System.out.println("My effectively final variable has value: " + a);
}
Here, a is not declared final, but it is considered effectively final since it is never changed.
Starting with Java 8, this can be used in the following way:
public void myMethod() {
int a = 1;
Runnable r = new Runnable() {
@Override
public void run() {
System.out.println("My effectively final variable has value: " + a);
}
};
}
In Java 7 and earlier versions, a had to be declared final to be able to be used in an local class like this, but from Java 8 it is enough that it is effectively final.
According to the docs:
A variable or parameter whose value is never changed after it is initialized is effectively final.
