用数组结构实现大小固定的栈

public class StackByArrary {

	private Integer[] arr;
	private Integer size;
	
	public  StackByArrary(int initSize){
		if(initSize<0){
			throw new IllegalArgumentException("The init size is less than 0");
		}
		arr=new Integer[initSize];
		size=0;
	}
	
	/**
	 * 返回栈顶的元素但是不移除
	 * @return
	 */
	public Integer peek(){
		if(size==0){
			return null;
		}
		return arr[size-1];
	}
	
	/**
	 * 返回栈顶的元素并移除
	 * @return
	 */
	public Integer pop(){
		if(size==0){
			throw new IllegalArgumentException("The stack is null");
		}
		return arr[--size];
	}
	
	
	public void push(Integer num){
		if(size==arr.length){
			throw new ArrayIndexOutOfBoundsException("The stack is empty");
		}
		arr[size++]=num;
	}

}