使用数组实现栈

//使用数组来实现栈package 数组实现栈;import java.util.Arrays;interface StackADT {    public void push(Object element);//压栈    public Object pop();//出栈    public boolean isEmpty();//判断是否为空栈    public int size();    public Object peek();    public String toString();}public class Stack implements StackADT {    private final int DEFAULT_SIZE = 3;  //默认数组大小    private int size = 0;    private int capacity = 0;    //top指向下一个能够添加元素的位置      private int top = 0;    private Object[] array;    public Stack() {//设置数组初始大小        this.capacity = this.DEFAULT_SIZE;        this.array = new Object[this.capacity];        this.size = 0;    }    public Stack(int capacity) {  //控制数组容量        this.capacity = capacity;        this.array = new Object[this.capacity];        this.size = 0;    }    @Override    public void push(Object element) {        //压栈        if (this.size < this.capacity) {            this.array[top] = element;            this.top++;            this.size++;        } else {            enlarge();            push(element);        }    }    public void enlarge() {   //扩容        this.capacity = this.capacity + this.DEFAULT_SIZE;        Object[] newArray = new Object[this.capacity];        System.arraycopy(array, 0, newArray, 0, array.length);        Arrays.fill(array, null);        this.array = newArray;    }    @Override    public Object pop() { //查看栈顶元素并将栈顶元素删除        Object element = (Object) this.array[top - 1];        this.array[top - 1] = null;        this.size--;        return element;    }    @Override    public boolean isEmpty() { //判断栈是否为空        return size == 0;    }    @Override    public int size() { //返回栈的大小        return size;    }    @Override    public Object peek() {   //查看栈顶元素但不删除        return (Object) this.array[this.top - 1];    }    public static void main(String[] args) {        Stack s = new Stack();        s.push(1);        s.push(2);        s.push(3);        System.out.println(s.pop());        System.out.println(s.size());    }}