The Java Type System - Java in a Nutshell - page 163

features of member classes. It is usually more appropriate to think of them as an
entirely separate kind of nested type.

See Chapter 5 for details as to when it's appropriate to choose
a local class versus a lambda expression.

The defining characteristic of a local class is that it is local to a block of code. Like a
local variable, a local class is valid only within the scope defined by its enclosing
block. Example 4-3 shows how we can modify the iterator() method of the
LinkedStack class so it defines LinkedIterator as a local class instead of a member
class.

By doing this, we move the definition of the class even closer to where it is used and
hopefully improve the clarity of the code even further. For brevity, Example 4-3
shows only the iterator() method, not the entire LinkedStack class that
contains it.

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Example 4-3. Deining and using a local class

// This method returns an Iterator object for this LinkedStack
public Iterator < Linkable > Iterator () {
// Here's the definition of LinkedIterator as a local class
class LinkedIterator implements Iterator < Linkable > {
Linkable current ;

// The constructor uses a private field of the containing class
public LinkedIterator () { current = head ; }

// The following 3 methods are defined by the Iterator interface
public boolean hasNext () { return current != null ; }

public Linkable next () {
if ( current == null )
throw new java . util . NoSuchElementException ();
Linkable value = current ;
current = current . getNext ();
return value ;
}

public void remove () { throw new UnsupportedOperationException (); }
}

// Create and return an instance of the class we just defined
return new LinkedIterator ();
}