自己实现一个栈(Stack)和队列(Queue)

需求

实现一个栈(Stack)和队列(Queue).

栈：后进先出
队列：先进先出

图示

栈

队列

代码

栈 (数组实现)

import java.util.Arrays;
import java.util.NoSuchElementException;

public class Stack<T> {
private static final int DEFAULT_CAPACITY = 10;

private Object[] elementData;

private int top;

public Stack() {
        initStack();
    }

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

private void initStack() {
        top = -1;
        ensureCapacity(DEFAULT_CAPACITY);
    }

public void push(T t) {
if (top + 1 == elementData.length)
            ensureCapacity((elementData.length << 1) + 1);
        elementData[++top] = t;
    }

public T pop() {
if (empty())
throw new NoSuchElementException();
return (T) elementData(top--);
    }

public boolean empty() {
return top == -1;
    }

private void ensureCapacity(int newCapacity) {
if (top + 1 >= newCapacity)
return;
        Object[] old = elementData;
        elementData = new Object[newCapacity];
for (int i = 0; i <= top; i++) {
            elementData[i] = old[i];
        }
    }

@SuppressWarnings("unchecked")
private T elementData(int index) {
return (T) elementData[index];
    }

@Override
public String toString() {
return Arrays.toString(elementData);
    }
}

队列 (链表实现)

public class Queue<T> {
public Node<T> beginMarker;

public Node<T> endMarker;

public int size;

public Queue() {
        initQueue();
    }

private void initQueue() {
        beginMarker = new Node<T>(null, null, null);
        endMarker = new Node<T>(null, beginMarker, null);
        beginMarker.next = endMarker;
        size = 0;
    }

public int size() {
return size;
    }

public boolean empty() {
return size == 0;
    }

public void enqueue(T t) {
        beginMarker.next = beginMarker.next.prev = new Node<T>(t, beginMarker,
                beginMarker.next);
        size++;
    }

public T dequeue() {
if (size == 0)
return null;
        Node<T> p = endMarker.prev;
        p.prev.next = endMarker;
        endMarker.prev = p.prev;
        size--;
return p.data;
    }

private static class Node<T> {
public T data;

public Node<T> prev;

public Node<T> next;

public Node(T data, Node<T> prev, Node<T> next) {
this.data = data;
this.prev = prev;
this.next = next;
        }
    }
}