固定长度数组实现栈和队列

public class ArrayStack {
	private Integer[] arr;
	private Integer index;
	
	public ArrayStack(int initSize) {     //固定数组大小
		if (initSize < 0) {
			throw new IllegalArgumentException("this init size is less than 0");
		}
		arr = new Integer[initSize];
		index = 0;
	}
	
	public Integer peek() {
		if (index == 0) {
			return null;
		}
		return arr[index - 1];
	}
	
	public void push(int obj) {
		if (index == arr.length) {
			throw new ArrayIndexOutOfBoundsException("The queue is full");
		}
		arr[index++] = obj;
	} 
	
	public Integer pop() {
		if (index == 0) {
			throw new ArrayIndexOutOfBoundsException("The queue is empty");
		}
		return arr[--index];
	}
}

循环利用数组 设置start和end开始指向0，设置一个size元素与约束end，加入元素，size++，当size=数组长度时，不允许在加入元素，当end,start走到数组最后一个下标时，返回0位置

public class ArrayQueue {
	
	private Integer[] arr;
	private Integer size;
	private Integer start;
	private Integer end;
	
	public ArrayQueue(int initSize) {     //固定数组大小
		if (initSize < 0) {
			throw new IllegalArgumentException("this init size is less than 0");
		}
		arr = new Integer[initSize];
		size = 0;
		start = 0;
		end = 0;
	}
	
	public Integer peek() {
		if (size == 0) {
			return null;
		}
		return arr[start];
	}
	
	public void push(int obj) {
		if (size == arr.length) {
			throw new ArrayIndexOutOfBoundsException("The queue is full");
		}
		size++;
		arr[end] = obj;
		end = end == arr.length - 1 ? 0 : end + 1;   //看end是不是走到了最后面
	}
	
	public Integer pop() {
		if (size == 0) {
			throw new ArrayIndexOutOfBoundsException("The queue is empty");
		}
		size--;
		int temp = start;
		start = start == arr.length - 1 ? 0 : start + 1;   //看start是不是走到了最后面
		return arr[temp];
	}
}