Java's special syntax to access outer class

gistfile1.java

$ cat Outer.java
class Outer {
    class Inner {
        void foo() {
            System.out.println(Outer.this.x);
        }
    }
    private int x = 3;
    public static void main(String[] args) {
        Outer outer = new Outer();
        Inner inner = outer.new Inner();
        inner.foo();
    }
}
$ javac Outer.java
$ java Outer
3