CODEWITHSUNDEEP
javaarraylistcollectionsiteratoriterable
berione
berione

Reputation: 122

Passing “this” in java constructor

ı was trying to understand iterator method in arrayList and in the iterable method ı couldnt understand using of "this" inside of ""return new MyArrayListIterator(this);"" ı know how to use "this" but ı didnt see this type of "this" before. what is this ?

public class MyArrayList<T> implements Iterable<T> {

private static final int DEFAULT_CAPACITY = 10;

//private instance fields
private T [] m_objs;
private int m_curIndex; 

//private non-static methods
private T[] allocate(int capacity)
{
    T [] objs = (T[])new Object[capacity];

    if (m_curIndex != 0)
        for (int i = 0; i < m_curIndex; ++i)
            objs[i] = m_objs[i];

    return objs;
}

private class MyArrayListIterator<E> implements Iterator<E> {
    private MyArrayList<E> m_mc;
    private int m_curIndex;

    private MyArrayListIterator(MyArrayList<E> mc)
    {
        m_mc = mc;
        m_curIndex = -1;
    }

    public boolean hasNext()
    {
        return ++m_curIndex < m_mc.m_curIndex;      
    }

    public E next() 
    {           
        return m_mc.m_objs[m_curIndex];
    }       
}

//public constructors
public MyArrayList()
{
    m_objs = (T[])new Object[DEFAULT_CAPACITY];
}

public MyArrayList(int capacity)
{
    if (capacity <= 0)
        throw new IllegalArgumentException("Capacity must be non negative");

    m_objs = (T[])new Object[capacity];
}

//getters
public int capacity() { return m_objs.length;}
public int size() { return m_curIndex;} 

//public methods
public boolean add(T elem)
{
    if (m_objs.length <= m_curIndex)
        m_objs = allocate(m_objs.length * 2);

    m_objs[m_curIndex++] = elem;

    return true;        
}

public void clear()
{
    for (int i = 0; i < m_curIndex; ++i)
        m_objs[i] = null;

    m_curIndex = 0;
}

public void ensureCapacity(int minCapacity)
{       
    if (minCapacity <= 0 && minCapacity <= m_curIndex && m_objs.length > m_curIndex)
        m_objs = allocate(m_curIndex);
    else
        m_objs = allocate(minCapacity);     
}

public T get(int index)
{
    if (index < 0 || index >= m_curIndex)
        throw new IndexOutOfBoundsException("index overflow or underflow");     

    return m_objs[index];
}

public boolean isEmpty() { return m_curIndex == 0;}


public Iterator<T> iterator()
{
    return new MyArrayListIterator<T>(this);                
}

public T remove(int index)
{
    if (index < 0 || index >= m_curIndex) 
        throw new IndexOutOfBoundsException("index overflow or underflow");     

    T oldElem = m_objs[index];  

    //TODO:     

    m_curIndex--;

    return oldElem;
}

public void trimToSize()
{
    int capacity = 0;

    if (m_curIndex == 0)
        capacity = DEFAULT_CAPACITY;
    else
        capacity = m_curIndex;

    m_objs = allocate(capacity);
}

public T[] toArray()
{
    return allocate(m_curIndex);
}

}

Upvotes: 0

Views: 135

Answers (2)

Mohammed Aouf Zouag
Mohammed Aouf Zouag

Reputation: 17142

return new MyArrayListIterator<T>(this);

this refers to the Iterable MyArrayList. Your method should return an Iterator on MyArrayList, so calling

return this;

would be wrong.

Upvotes: 1

Suresh Atta
Suresh Atta

Reputation: 122008

where ever and when ever you see this, it always points to the current instance of the object. In this case it's points to MyArrayListIterator<E> 

public Iterator<T> iterator()
{
    return new MyArrayListIterator<T>(this);                
}

Means the type MyArrayListIterator is Iterator, and using the constructor this you are referring to the constructor 

private MyArrayListIterator(MyArrayList<E> mc)
    {
        m_mc = mc;
        m_curIndex = -1;
    }

Upvotes: 0

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