Accessing Outer class attribute from an instance of an Inner class

Question

Given the following code:

public class Outer
{
   public final int n;
   public class Inner implements Comparable<Inner>
   {
      public int compareTo(Inner that) throws ClassCastException
      {
          if (Outer.this.n != Outer.that.n) // pseudo-code line
          {
               throw new ClassCastException("Only Inners with the same value of n are comparable");
//...

What can I swap out with my pseudo-code line so that I can compare the values of n for the two instances of the Inner class?

Trying the obvious solution (n != that.n) doesn't compile:

Outer.java:10: cannot find symbol
symbol  : variable n
location: class Outer.Inner
                    if (n != that.n) // pseudo-code line

miku · Accepted Answer · 2009-11-21 18:13:40Z

7

As with instance methods and variables, an inner class is associated with an instance of its enclosing class and has direct access to that object's methods and fields. - Java OO

You could write a getter method in the inner class, which returns n of the outer class.

Method on Inner:

public int getOuterN() { return n; }

Then compare using this method:

getOuterN() != that.getOuterN()

edited Nov 21, 2009 at 18:13

answered Nov 21, 2009 at 17:31

miku

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3 Comments

rampion Over a year ago

n is a public attribute of Outer, and not accessible as an attribute of that. Trying this gives a "cannot find symbol" error

miku Over a year ago

somebody copied my first answer ;) - does n!= that.n work after all?

rampion Over a year ago

I wound up going with the slightly more general public Outer parent() { return Outer.this; } so I could access all the members I needed to.

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