栈具有先进后出的特性。栈和队列一样，同样是一种特殊的列表。本文将介绍栈的基本接口及数组栈、链栈的Java实现。

源码

public interface IStack {
    void push(T data); // 入栈
    T peek(); // 取栈顶元素
    T pop(); // 出栈
    int size(); // 长度
    boolean isEmpty(); // 是否为空
}

源码
测试类

public class MyArrayStack implements IStack {

    private T[] datas;
    int count = 0; // 栈长度,兼栈顶指针
    int capacity; // 数组容量

    public MyArrayStack(int capacity) {
        this.capacity = capacity;
        this.datas = (T[]) new Object[capacity];
    }

    @Override
    public void push(T data) {
        if (count == capacity)
            throw new RuntimeException("栈已满");
        this.datas[count++] = data;
    }

    @Override
    public T peek() {
        if (isEmpty())
            throw new RuntimeException("栈为空");
        return datas[count - 1];
    }

    @Override
    public T pop() {
        if (isEmpty())
            throw new RuntimeException("栈为空");
        return datas[--count];
    }

    @Override
    public int size() {
        return count;
    }

    @Override
    public boolean isEmpty() {
        return count == 0;
    }
}

源码
测试类

public class MyLinkedStack implements IStack {

    private class Node {
        T data;
        Node next;
        Node() {}
        Node(T data) {
            this.data = data;
        }
        Node(T data, Node next) {
            this.data = data;
            this.next = next;
        }
    }

    private Node top = new Node(); // 栈顶为top.next
    private int count = 0;

    @Override
    public void push(T data) {
        Node node = new Node(data, top.next);
        top.next = node;
        count++;
    }

    @Override
    public T peek() {
        if (isEmpty())
            throw new RuntimeException("栈为空");
        return top.next.data;
    }

    @Override
    public T pop() {
        if (isEmpty())
            throw new RuntimeException("栈为空");
        T res = top.next.data;
        top = top.next;
        count--;
        return res;
    }

    @Override
    public int size() {
        return count;
    }

    @Override
    public boolean isEmpty() {
        return count == 0;
    }
}

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数据结构——栈

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