StackArray 一个栈类

public class StackArray implements Stack {

private final int LEN = 4; //数组的默认大小
private Object[] elements; //数据元素数组
private int top; //栈顶指针

public StackArray() {
top = -1;
elements = new Object[LEN];
}

//返回堆栈的大小
public int getSize() {
return top+1;
}

//判断堆栈是否为空
public boolean isEmpty() {
return top<0;
}

//数据元素e入栈
public void push(Object e) {
if (getSize()>=elements.length) expandSpace();
elements[++top] = e;
}

private void expandSpace(){
Object[] a = new Object[elements.length*2];
for (int i=0; i<elements.length; i++)
a[i] = elements[i];
elements = a;
}

//栈顶元素出栈
public Object pop() throws StackEmptyException {
if (getSize()<1)
throw new StackEmptyException("错误，堆栈为空。");
Object obj = elements[top];
elements[top--] = null;
return obj;
}

//取栈顶元素
public Object peek() throws StackEmptyException {
if (getSize()<1)
throw new StackEmptyException("错误，堆栈为空。");
return elements[top];
}
}