手动实现ArrayList 之数组扩容(3)

版权声明： https://blog.csdn.net/weixin_40072979/article/details/82868882

package com.jianshun;

/**自定义实现一个ArrayList,体会底层原理
 * 增加数组扩容
 * @author Administrator
 *
 */
public class SxtArrayList03<E> {

	private Object[] elementData;
	private int size;
	
	private static final int DEFAULT_CAPACITY=10;
	
	public SxtArrayList03(){
		elementData =new Object[DEFAULT_CAPACITY];
	}
	
	public SxtArrayList03(int capacity){
		elementData  = new Object[capacity];
	}
	
	public void add(E element){
		//什么时候扩容
		if(size == elementData.length){
			//扩容操作
			Object[] newArray = new Object[elementData.length + (elementData.length >> 1)];//10-->10+5
			System.arraycopy(elementData,0,newArray,0,elementData.length);
			elementData  = newArray;
		}
		elementData[size++] = element;
	}
	
	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder();		
		sb.append("[");
		for(int i=0;i<size; i++){
			sb.append(elementData[i]+",");
		}
		sb.append("]");
		return sb.toString();
	}
	
	public static void main(String[] args) {
		SxtArrayList03 s1 = new SxtArrayList03();
		
		for(int i=0;i<200; i++){
			s1.add("gao"+i);
		}
		
		System.out.println(s1);
	}
}