数组实现线程安全的栈

package quiz;/** * 线程安全的栈实现，固定10容量，扩展容量没有用到 * */public class StackImplUseArray {private Object[] objs = new Object[10];//栈元素private int index;//栈指针/** * 压栈操作 * */public synchronized void push(Object obj)throws OverFlowException{if(objs.length <= index){throw new OverFlowException("栈空间已用完!");}objs[index++] = obj;}/** * 出栈操作 * */public synchronized Object pop()throws NullPointerException{if(index == 0){throw new NullPointerException("棧里没有元素!");}return objs[index--];}private void expand(){Object[] objs = new Object[this.objs.length*2];System.arraycopy(this.objs, 0, objs, 0, index);this.objs = objs;}}