Java 数组实现 stack

 首先定义 IStack

package cn.com.example.stack;

/**
 * Created by Jack on 2017/3/8.
 */
public interface IStack<T> {

    //元素出栈，并返回出栈元素
    public T pop() throws IllegalAccessException;

    //元素入栈
    public void push(T element);

    //获取栈顶元素
    public T peek() throws IllegalAccessException;

    //判断栈是否为空
    public boolean isEmpty();

    // 栈大小
    public int size();

    public void clear();
}

接着定义 MyStack 实现 IStack接口  并测试

package cn.com.example.stack;

import java.util.Arrays;

/**
 * Created by Jack on 2017/3/8.
 */
public class MyStack<T> implements IStack {

    private final int DEFAULT_SIZE = 3;
    private int size = 0;
    private int capacity = 0;

    //top指向下一个可以添加元素的位置
    private int top = 0;
    private Object[] array;

    public MyStack() {
        this.capacity = this.DEFAULT_SIZE;
        this.array = new Object[this.capacity];
        this.size = 0;
    }

    public MyStack(int capacity) {
        this.capacity = capacity;
        this.array = new Object[this.capacity];
        this.size = 0;
    }


    /**
     * 元素出栈，并返回出栈元素
     *
     * @return
     */
    @Override
    public Object pop() throws IllegalAccessException {
        if (this.size == 0)
            throw new IllegalAccessException("stack element empty");
        T element = (T) this.array[top - 1];
        this.array[top - 1] = null;
        this.size--;
        this.top--;
        return element;
    }

    /**
     * 元素入栈
     *
     * @param element
     */
    @Override
    public void push(Object element) {
        if (this.size < this.capacity) {
            this.array[this.top] = element;
            this.top++;
            this.size++;
        } else {
            // 扩容
            enlarge();
            push(element);
        }
    }

    private void enlarge() {
        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;
    }

    /**
     * 获取栈顶元素
     *
     * @return
     */
    @Override
    public Object peek() throws IllegalAccessException {
        if (this.size == 0)
            throw new IllegalAccessException("stack element empty");
        return this.array[this.top - 1];
    }

    /**
     * 判断栈是否为空
     *
     * @return
     */
    @Override
    public boolean isEmpty() {
        return size == 0;
    }

    /**
     * 获取栈大小
     *
     * @return
     */
    @Override
    public int size() {
        return size;
    }

    /**
     * 清空 栈
     */
    @Override
    public void clear() {
        Arrays.fill(array, null);
        this.capacity = this.DEFAULT_SIZE;
        this.array = new Object[this.capacity];
        this.size = 0;
        this.top = 0;
    }
}

class MyStackTest {
    public static void main(String[] args) throws IllegalAccessException {
        MyStack<String> stack = new MyStack<String>();

        stack.push("1");

        // 栈头
        System.out.println(stack.peek());

        // 栈头出栈
        System.out.println(stack.pop());

        // 是否为空
        System.out.println(stack.isEmpty());

        System.out.println(stack.size());

        for (int i = 1; i <= 10; i++) {
            stack.push("" + i);
        }

        System.out.println(stack.size());

        for (int i = 0; i < 10; i++) {
            String s = (String) stack.pop();
            System.out.println(s);
        }

        // 清空
        //stack.clear();

        System.out.println("size = " + stack.size());
    }
}

输出

1
1
true
0
10
10
9
8
7
6
5
4
3
2
1
size = 0