栈

API

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
import java.util.Iterator;

public class Stack<E> implements Iterable<E> {
    
    /**
     * 入栈
     */
    void push(E element);

    /**
     * 弹出栈顶端元素，若栈为空，则抛出 IllegalArgumentException
     */
    public E pop();

    /**
     * 栈元素个数
     */
    public int size();

    /**
     * 栈是否为空
     */
    public boolean isEmpty();

    /**
     * 迭代器
     */
    @Override
    public Iterator<E> iterator();
}

实现

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
public class Stack<E> implements Iterable<E> {

    private static class Node<T> {
        Node<T> next;
        T item;

        Node(Node<T> next, T item) {
            this.next = next;
            this.item = item;
        }
    }

    /**
     * 栈顶元素
     */
    private Node<E> top;

    /**
     * 栈元素个数
     */
    private int size;

    /**
     * 入栈
     */
    void push(E element) {
        top = new Node<>(top, element);
        size++;
    }

    /**
     * 弹出栈顶端元素，若栈为空，则抛出异常
     */
    public E pop() {
        if (isEmpty()) {
            throw new IllegalArgumentException("empty stack");
        }
        Node<E> temp = top;
        top = top.next;
        temp.next = null; // help gc
        size--;
        return temp.item;
    }

    /**
     * 栈元素个数
     */
    public int size() {
        return size;
    }

    /**
     * 栈是否为空
     */
    public boolean isEmpty() {
        return top == null;
    }

    /**
     * 迭代器
     */
    @Override
    public Iterator<E> iterator() {
        return new StackIterator();
    }

    private class StackIterator implements Iterator<E> {
        Node<E> current = top;

        @Override
        public boolean hasNext() {
            return current != null;
        }

        @Override
        public E next() {
            Node<E> oldCurrent = current;
            current = current.next;
            return oldCurrent.item;
        }
    }
}

测试

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
public static void main(String[] args) {
        Stack<Integer> stack = new Stack<>();
        for (int i = 0; i < 5; i++) {
            stack.push(i);
        }
        System.out.println("stack size is : " + stack.size()); //output: 5

        for (int i : stack) {
            System.out.print(i); // output: 43210
        }
        System.out.println();
        for (int i = 0; i < 5; i++) {
            stack.pop();
        }
        System.out.println("stack size is : " + stack.size()); // output: 0
        System.out.println("stack is empty : " + stack.isEmpty()); // output: true
    }