ArrayList.java

package com.coding.basic;

public class ArrayList implements List {
	
	private int size = 0;
	private Object[] elementData = new Object[10];
	
	public void add(Object o){
		if(size < this.elementData.length){//加至末尾，size+1
			this.elementData[size] = o;
			size++;
		}else{//扩张数组，然后加至末尾，size+1
			this.elementData = grow(this.elementData,10);
			this.elementData[size] = o;
			size++;
		}
	}
	
	public void add(int index, Object o){//-1<index<size+1 or 0=<index<=size
		if(index < 0 || index > this.size){//index小于0or大于size，参数错误
			return;
		}
		if(size >= this.elementData.length){//当前数组容量已满，需扩张
			this.elementData = grow(this.elementData, 10);
		}
		
		//此时只需考虑将o加至index处（0=<index<=size && size<length）
		if(index < size){//移动数据，然后插入o，size+1
			for(int i = size;i > index;i--){
				this.elementData[i] = this.elementData[i-1];
			}
			this.elementData[index] = o;
			this.size++;
		}else{//直接插入o，size+1
			this.elementData[index] = o;
			this.size++;
		}
		
	}
	
	public Object get(int index){//-1<index<size  or 0=<index<size
		if(index < 0 || index >= this.size){//index小于0or大于等于size，参数错误
			return null;
		}
		return this.elementData[index];
	}
	
	public Object remove(int index){//-1<index<size  or 0=<index<size
		if(index < 0 || index >= this.size){//index小于0or大于等于size，参数错误
			return null;
		}
		
		Object o = this.elementData[index];//o保存被移除的值
		//此时只需考虑将index处的o移除
		for(int i = index;i < this.size-1;i++){
			this.elementData[i] = this.elementData[i+1];
		}
		this.size--;
		return o;
	}
	
	public int size(){
		return this.size;
	}
	
	public Iterator iterator(){
		return new ArrayListIterator(this);
	}
	
	public static class ArrayListIterator implements Iterator{
		private ArrayList list;
		private int pres;
		
		public ArrayListIterator(ArrayList list) {
			super();
			this.list = list;
			this.pres = 0;
		}

		@Override
		public boolean hasNext() {
			if(this.pres < this.list.size()){
				return true;
			}else{
				return false;
			}
		}

		@Override
		public Object next() {
			Object o = this.list.get(this.pres);
			this.pres++;
			return o;
		}
		
	}
	
	/*
	 * 说明：扩张数组
	 * 参数：被扩张的原数组，扩张的增加数（扩张后数组的大小为原数组的长度+增加数）
	 * 返回值：扩张后的数组
	 */
	private static Object[] grow(Object[] src,int size){
//		return Arrays.copyOf(src, src.length + size);
		Object[] target = new Object[src.length + size];
		System.arraycopy(src, 0, target, 0, src.length);
		return target;
	}
	
	public String toString(){
		String result = "[";
		if(this.size == 0){
			result = result + "]";
			return result;
		}else{
			for(int i = 0;i < size;i++){
				result = result + this.elementData[i] + ",";
			}
			result = result.substring(0,result.length()-1);
			result = result + "]";
			return result;
		}
	}
	
}