Iterator

java에서 Iterator가 뭘까?

Iterator (반복자)
반복적인 작업을 수행하는 것.

 

 - Main.java

public class Main{
	public static void main(String[] args){
		ArrayList numbers = new ArrayList();
		numbers.addLast(10);
		numbers.addLast(20);
		numbers.addLast(30);
		numbers.addLast(40);


        for(int i=0;i<numbers.size();i++){
            System.ot.println(numbers.get(i));
        }

		ArrayList.ListIterator li = numbers.listIterator();
        //numbers 객체의 반복적인 작업 수행을 위해서는 ArrayList의 ListIterator라는 객체가 필요
        
        while(li.hasNext()){
        	System.out.println(li.next());
        }
        //10 20 30 40 print됨
        
        while(li.hasPrevious()){
        	System.out.println(li.previous());
        }
        //40 30 20 10 print됨
        
}

 

 - ArrayList.java

public Object removeFirst(){
	return remove(0);
}

public Object removeLast(){
	return remove(size-1);
}

public Object get(int index){
	return elementData[index];
}

public int size(){
	return size;
}

public int indexOf(Object o){
    for(int i=0 ; i<size ; i++){
        if(o.equals(elementData[i])){
        	return i;
        }
    return -1;
    }
}

public ListIterator listIterator(){
	return new ListIterator();
}

class ListIterator{
	private int nextIndex = 0;
    
    public boolean hasNext(){
    	return nextIndex < size();
    }
    
	public Object next(){
    	return elementData[nextIndex++];
    }
    
    public boolean hasPrevious(){
    	return nextIndex > 0;
    }
    
    public Object previous(){
    	return elementData[--nextIndex];
    }
    
    public void add(Object element){
    	ArrayList.this.add(nextIndex++, element);
        //element를 넣을 index인 nextIndex를 매개변수로 넣어주고,
        //element를 넣은 후 nextIndex를 1 증가시켜줌.
    }
    
    public void remove(){
    	ArrayList.this.remove(nextIndex-1);
        nextIndex--;
    }
}