Inner Classes – Ken Lambert

Python

Java

A class might be defined just for use in another class definition. For example, a LinkedStack class might use a OneWayNode class. Ideally, the definition of OneWayNode would be nested within LinkedStack, but that is not allowed. For the sake of comparison, here is an implementation of these two classes:

class OneWayNode:    def __init__(self, data, next):
        self.data = data
        self.next = next

class LinkedStack:

    def __init__(self):
        self.items = None
        self.size = 0

    def push(self, element):
        self.items = OneWayNode(element, self.items)
        self.size += 1

    def pop(self):
        element = self.items.data
        self.items = self.items.next
        self.size -= 1
        return element

def peek(self):
return self.items.data

def isEmpty(self):
return len(self) == 0

def __len__(self):
return self.size

A class might be defined just for use in another class definition. For example, a LinkedStack class might use a OneWayNode class. The definition of OneWayNode can be nested within LinkedStack. OneWayNode is specified as a private class, sometimes also called an inner class. Here is an implementation:

public class LinkedStack<E> implements TrueStack<E>{ private OneWayNode<E> items;
private int size;

    public LinkedStack(){
        this.items = null;
        this.size = 0;
    }

    public void push(E element){
        this.items = new OneWayNode<E>(element, items);
        this.size += 1;
    }

    public E pop(){
        E element = this.items.data;
        this.items = this.items.next;
        this.size -= 1;
        return element;
    }

    public E peek(){
        return this.items.data;
    }

    public boolean isEmpty(){
        return this.size() == 0;
    }

    public int size(){
        return this.size;
    }

    public Iterator<E> iterator(){
        return null;                 # Deferred to another
    }                                # topic

private class OneWayNode<E>{

private E data;
private OneWayNode next;

        private OneWayNode(E data, OneWayNode next){
            this.data = data;
            this.next = next;
        }
    }
}