（java）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());


    }


}