Java实现栈

数组栈：压栈、出栈、返回栈顶元素

public interface StackADT<T> {

    /**
     * 压栈
     * */
    public void push(T element);

    /**
     * 出栈
     * */
    public T pop();

    /**
     * 返回栈顶元素
     * */
    public T peek();

    public boolean isEmpty();

    public int size();

}

public class ArrayStack<T> implements StackADT<T> {

    private Object[] data = null;
    private Integer maxSize = 0;
    private Integer top = -1;

    ArrayStack() {
        this(10);
    }

    ArrayStack(int initialSize) {
        if (initialSize >= 0) {
            this.maxSize = initialSize;
            data = new Object[initialSize];
            top = -1;
        } else {
            throw new RuntimeException("初始化大小不能小于0：" + initialSize);
        }
    }

    @Override
    public void push(T element) {
        if (top != maxSize - 1)
            data[++top] = element;
        else
            throw new RuntimeException("栈已满，压栈失败！");
    }

    @Override
    public T pop() {
        if (top != -1)
            return (T) data[top--];
        else
            throw new RuntimeException("栈为空！");
    }

    @Override
    public T peek() {
        if (top != -1)
            return (T) data[top];
        else
            throw new RuntimeException("栈为空！");
    }

    @Override
    public boolean isEmpty() {
        return top != -1 ? false : true;
    }

    @Override
    public int size() {
        return top + 1;
    }

    @Override
    public String toString() {
        return top != -1 ? "容量=" + maxSize + "\n栈内容=" + Arrays.toString(data)
                + "\n栈顶元素=" + peek() : "栈为空！";
    }

}

链式栈：压栈、出栈、返回栈顶元素

public class LinkStack<T> implements StackADT<T> {

    private class Node {

        T t;
        Node next;

        public Node(T t, Node next) {
            this.t = t;
            this.next = next;
        }

    }

    private Node top;
    private int size;

    public LinkStack() {
        top = null;
    }

    @Override
    public void push(T element) {
        top = new Node(element, top);
        size++;
    }

    @Override
    public T pop() {
        if (isEmpty()) {
            throw new RuntimeException("栈为空！");
        } else {
            Node value = top; // 得到栈顶元素
            top = top.next; // 让top引用指向原栈顶元素的下一个元素
            value.next = null; // 释放原栈顶元素的next引用
            size--;
            return value.t;
        }
    }

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

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

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

    @Override
    public String toString() {
        return isEmpty() ? "栈为空！" : "LinkStack [top=" + top.t + ", size="
                + size + "]";
    }

}