Accessing outer class variable in inner class

Question

In inner classes, variables of outer class are accessible, but local variables of a method are not. I understood the part about local variables of a method not being accessible but I want to know why outer class variables are accessible?

My understanding is that as an inner class binds with the outer class, so as long as the parent is available, the child can access its parent variables. Am I correct?

@DuncanJones: inner classes are always non-static. Have a look at here.. http://docs.oracle.com/javase/tutorial/java/javaOO/nested.html — Vishal K, Jul 10 '13 at 19:07
@VishalK Thanks, I've been mistakenly calling nested classes *inner classes* for years. Whoops! — Duncan Jones, Jul 10 '13 at 19:11
I think this post is later than op's time when s/he asked, but it is a good reference https://www.programiz.com/java-programming/nested-inner-class — helloworld, Sep 24 '20 at 00:52

score 64 · Accepted Answer · answered Jul 10 '13 at 19:05

64

Assuming your outer class is called Outer, from the scope of the inner class(non-static), Outer.this.foo to get at the field.

For example,

Outer.this.foo=new ArrayList<>();

where Outer is the name of the class and foo identifies the field.

You can also grab it directly as foo=new Baz() but it'll pick the inner field if there's a naming conflict due to shadowing.

if it's a static inner class, you need an explicit instance:

outerInstance.foo=new ArrayList<>();

or if the field to access is static, access it as usual with:

Outer.staticFoo=new ArrayList<>();

answered Jul 10 '13 at 19:05

nanofarad

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Hi, thanks for reply,Here my question is if inner class and outer class uses the variable at a time there might be a chance of concurrent issues.But, the inner classes uses variable as how two methods of a class use.so, we should need to use synchhronization to handle this with inner class. – kiran Jul 13 '13 at 20:04
1

@user5 No, not beyond any synchronization you would need to do in any other case. Inner and outer classes do not cause new threads to be created. – nanofarad Jul 13 '13 at 20:19

score 2 · Answer 2 · answered Feb 10 '16 at 11:57

Answer: Outer class variables in java are accessible because of lexical scope.

What is a lexical scope?

The scope defined in order in which code is authored. Lets say your class structure is as follows

OuterMost  
   --Inner  
     --InnerMost

Then the inner most class will be able to access variables from inner as well outer most.

Accessing outer class variable in inner class

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