Accessing Members of an Enclosing Class

A local class has access to the members of its enclosing class. In the previous example, the 

PhoneNumber

 constructor
accesses the member 

LocalClassExample.regularExpression

.

In addition, a local class has access to local variables. However, a local class can only access local variables that are declared final. When a local class accesses a local variable or
parameter of the enclosing block, it captures that variable or parameter. For example, the 

PhoneNumber

 constructor can access the local variable 

numberLength

 because
it is declared final; 

numberLength

 is acaptured variable.
However, starting in Java SE 8, a local class can access local variables and parameters of the enclosing block that
are final or effectively final. A variable or parameter whose value is never changed after it is initialized is effectively final. For example, suppose that the variable 

numberLength

 is
not declared final, and you add the highlighted assignment statement in the 

PhoneNumber

 constructor:

PhoneNumber(String phoneNumber) {
numberLength = 7;
String currentNumber = phoneNumber.replaceAll(
regularExpression, "");
if (currentNumber.length() == numberLength)
formattedPhoneNumber = currentNumber;
else
formattedPhoneNumber = null;
}

Because of this assignment statement, the variable 

numberLength

 is not effectively final anymore. As a result, the Java compiler
generates an error message similar to "local variables referenced from an inner class must be final or effectively final" where the inner class 

PhoneNumber

 tries to access the 

numberLength

 variable:

if (currentNumber.length() == numberLength)

Starting in Java SE 8, if you declare the local class in a method, it can access the method's parameters. For example, you can define the following method in the 

PhoneNumber

 local
class:

public void printOriginalNumbers() {
System.out.println("Original numbers are " + phoneNumber1 +
" and " + phoneNumber2);
}

The method 

printOriginalNumbers

 accesses the parameters 

phoneNumber1

 and 

phoneNumber2

 of
the method 

validatePhoneNumber

.