Java 集合的简单实现 (ArrayList & LinkedList & Queue & Stack)

ArrayList

就是数组实现的啦，没什么好说的，如果数组不够了就扩容到原来的1.5倍

实现了迭代器

package com.wenr.collection;

import java.io.Serializable;
import java.util.Arrays;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.RandomAccess;

/**
 * @author wenr
 * 
 *   实现方法：
 * - void add(E e)
 * - void add(int index, E e)
 * - E get(int index)
 * - int indexOf(Object o)
 * - boolean contains(Object o)
 * - int size()
 * - boolean isEmpty()
 * - E remove(int index)
 * - boolean remove(Object o)
 * - Iterator<E> iterator()
 * 
 */
public class ArrayListDemo<E> implements RandomAccess, Cloneable, Serializable{
    
    private static final int DEFAULT_SIZE = 10;
    
    private Object[] elementData;
    private int size = 0;
    
    ArrayListDemo() {
        this(DEFAULT_SIZE);
    }
    
    ArrayListDemo(int initialCapacity) {
        if (initialCapacity < 0) {
            throw new IllegalArgumentException("初始化参数错误：" + initialCapacity);
        } else {
            elementData = new Object[initialCapacity];
        }
    }
    
    public void add(E e) {
        isCapacityEnough(size + 1);
        elementData[size++] = e;
    }
    
    public void add(int index, E e) {
        rangeCheckForAdd(index);
        isCapacityEnough(size + 1);
        System.arraycopy(elementData, index, elementData, index + 1, size - index);
        elementData[index] = e;
        size++;
    }
    
    private void rangeCheckForAdd(int index) {
        if (index < 0 || index > size)
            throw new IndexOutOfBoundsException("下标越界：" + index);
    }
    
    private void isCapacityEnough(int capacity) {
        // 溢出
        if (capacity < 0)
            throw new OutOfMemoryError();
        // 需要扩容
        if (capacity - elementData.length > 0)
            grow(capacity);
    }
    
    private void grow(int capacity) {
        int oldCapacity = elementData.length;
        // 设置新容量是原容量的1.5倍
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        // 可能会有一次加入多个数据的情况 那么久直接加到所需容量
        if (capacity - newCapacity > 0)
            newCapacity = capacity;
        elementData = Arrays.copyOf(elementData, newCapacity);
    }
    
    public E get(int index) {
        rangeCheck(index);
        return (E)elementData[index];
    }
    
    private void rangeCheck(int index) {
        if (index < 0 || index >= size) 
            throw new IllegalArgumentException("下标越界：" + index);
    }
    
    public int indexOf(Object o) {
        if (o == null) {
            for (int i = 0; i < size; ++i) {
                if (elementData[i] == null)
                    return i;
            }
        } else {
            for (int i = 0; i < size; ++i) {
                if (o.equals(elementData[i]))
                    return i;
            }
        }
        return -1;
    }
    
    public boolean contains(Object o) {
        return indexOf(o) >= 0;
    }
    
    public int size() {
        return size;
    }
    
    public boolean isEmpty() {
        return size == 0;
    }
    
    public E remove(int index) {
        rangeCheck(index);
        E value = (E)elementData[index];
        int moveSize = size - index - 1;
        if (moveSize > 0)
            System.arraycopy(elementData, index + 1, elementData, index, moveSize);
        elementData[--size] = null;
        return value;
    }
    
    public boolean remove(Object o) {
        int index = indexOf(o);
        if (index < 0) {
            return false;
        } else {
            remove(index);
            return true;
        }
    }
    
    public Iterator<E> iterator() {
        return new Itr();
    }
    
    private class Itr implements Iterator<E> {
        
        int cursor = 0;            // 下一个将返回的元素

        @Override
        public boolean hasNext() {
            return cursor != size;
        }

        @Override
        public E next() {
            if (cursor < 0 || cursor >= size)
                throw new NoSuchElementException();
            Object[] elementData = ArrayListDemo.this.elementData;
            return (E)elementData[cursor++];
        }
        
    }
    

    public static void main(String[] args) {
        ArrayListDemo<String> list = new ArrayListDemo<String>();
        list.add("1");
        list.add("2");
        list.add("3");
        System.out.println(list.get(0));
        System.out.println(list.get(1));
        System.out.println(list.get(2));
        System.out.println(list.indexOf("3"));
        System.out.println(list.remove("3"));
        System.out.println(list.contains("3"));
        // System.out.println(list.get(3));
        Iterator<String> itr = list.iterator();
        while (itr.hasNext()) {
            System.out.println(itr.next());
        }
    }
    
}

LinkedList

嗯，就是一个双向链表~

package com.wenr.collection;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * @author wenr
 * 
 *  实现方法:
 * - void add(E e)
 * - void add(int index, E e)
 * - E get(int index)
 * - int indexOf(Object o)
 * - boolean contains(Object o)
 * - E remove(int index)
 * - boolean remove(Object o)
 * - boolean isEmpty()
 * - int size()
 * - Iterator<E> iterator()
 *
 */
public class LinkedListDemo<E> {
    
    private int size;
    Node<E> first;
    Node<E> last;
    
    public LinkedListDemo() {
    }
    
    // 添加一个节点在结尾处
    public void add(E e) {
        Node<E> l = last;
        Node<E> node = new Node(e, last, null);
        last = node;
        if (l == null) {
            first = node;
        } else {
            l.next = node;
        }
        size++;
    }
    
    public void add(int index, E e) {
        rangeCheckForAdd(index);
        if (index == size) {
            add(e);
        } else {
            Node<E> x = node(index);
            addBeforeNode(e, x);
        }
    }
    
    private void rangeCheckForAdd(int index) {
        if (index < 0 || index > size)
            throw new IndexOutOfBoundsException("下标越界：" + index);
    }
    
    private void addBeforeNode(E e, Node<E> beforeNode) {
        Node<E> preNode = beforeNode.prev;
        Node<E> newNode = new Node(e, preNode, beforeNode);
        if (preNode == null) {
            first = newNode;
        } else {
            preNode.next = newNode;
        }
        beforeNode.prev = newNode;
        size++;
    }
    
    private Node<E> node(int index) {
        // 如果node在前一半就正向查找 否则逆向查找
        if (index < (size >> 1)) {
            Node<E> cursor = first;
            for (int i = 0; i < index; ++i) {
                cursor = cursor.next;
            }
            return cursor;
        } else {
            Node<E> cursor = last;
            for (int i = size-1; i > index; --i) {
                cursor = cursor.prev;
            }
            return cursor;
        }
    }
    
    public E get(int index) {
        rangeCheck(index);
        Node<E> x = node(index);
        return x.item;
    }
    
    private void rangeCheck(int index) {
        if (index < 0 || index >= size)
            throw new IndexOutOfBoundsException("数组越界：" + index);
    }
    
    public int indexOf(Object o) {
        int index = 0;
        if (o == null) {
            for (Node<E> x = first; x != null; x = x.next) {
                if (x.item == null)
                    return index;
                index++;
            }
        } else {
            for (Node<E> x = first; x != null; x = x.next) {
                if (o.equals(x.item))
                    return index;
                index++;
            }
        }
        return -1;
    }
    
    public E remove(int index) {
        rangeCheck(index);
        
        Node<E> x = node(index);
        final E element = x.item;
        final Node<E> prev = x.prev;
        final Node<E> next = x.next;
        
        if (prev == null) {
            first = next;
        } else {
            prev.next = next;
            x.prev = null;
        }
        
        if (next == null) {
            last = prev;
        } else {
            next.prev = prev;
            x.next = null;
        }
        
        x.item = null;
        size--;
        return element;
    }
    
    public boolean remove(Object o) {
        int index = indexOf(o);
        if (index < 0)
            return false;
        remove(index);
        return true;
    }
    
    public int size() {
        return size;
    }
    
    public boolean isEmpty() {
        return size == 0;
    }
    
    public boolean contains(Object o) {
        return indexOf(o) >= 0;
    }
    
    public Iterator<E> iterator() {
        return new Itr();
    }
    
    
    private static class Node<E> {
        E item;
        Node<E> prev;
        Node<E> next;
        public Node(E item, Node<E> prev, Node<E> next) {
            this.item = item;
            this.prev = prev;
            this.next = next;
        }
    }
    
    private class Itr implements Iterator<E> {
        
        private Node<E> cursor;
        private int nextIndex;
        
        public Itr() {
            cursor = first;
            nextIndex = 0;
        }

        @Override
        public boolean hasNext() {
            return nextIndex < size;
        }

        @Override
        public E next() {
            if (!hasNext())
                throw new NoSuchElementException();
            E element = cursor.item;
            cursor = cursor.next;
            nextIndex++;
            return element;
        }
        
    }
    
    public static void main(String[] args) {
        LinkedListDemo<String> list = new LinkedListDemo<>();
        list.add("aaaa");
        list.add("bbbb");
        list.add("cccc");
        list.add("dddd");
        System.out.println(list.size());
        System.out.println(list.get(1));
        System.out.println(list.get(2));
        System.out.println(list.get(0));
        System.out.println(list.remove(2));
        list.add(3, "eeee");
        System.out.println(list.get(1));
        System.out.println(list.get(2));
        System.out.println(list.get(3));
        System.out.println("_____");
        Iterator<String> itr = list.iterator();
        while (itr.hasNext()) {
            System.out.println(itr.next());
        }
    }
    
}

Queue

瞎写的啦哈哈哈

队列先进先出 用循环队列实现 节省空间

当front==tail就是队列为空

因为如果队列全部装满的时候front==tail，和空一样，所以循环队列不能全部装满，至少空出一位

当(tail+1)%capacity==front的时候就是队列满（capacity是队列容量大小

package com.wenr.collection;

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

/**
 * 
 * @author wenr
 *    
 *  通过数组实现的循环队列
 *    
 *  实现方法：
 * - boolean offer(E)
 * - boolean isEmpty()
 * - E peek()
 * - E poll()
 * - int size()
 *
 */

public class QueueDemo<E> {

    private static final int DEFAULT_SIZE = 0;
    
    private Object[] elementData;
    private int front;
    private int tail;
    
    public QueueDemo() {
        this(DEFAULT_SIZE);
    }
    
    public QueueDemo(int capacity) {
        elementData = new Object[capacity];
        front = tail = 0;
    }
    
    // 向队列中加入一个元素
    public boolean offer(E element) {
        int capacity = elementData.length;
        // 注意这里是capacity-1哦  因为要区别empty 所以循环队列不能装满的
        if (size() == capacity - 1) {
            grow(++capacity);
        }
        elementData[tail] = element;
        tail = (tail + 1) % capacity;
        return true;
    }
    
    // 获取并移除此队列的头
    public E poll() {
        if (isEmpty())
            throw new NoSuchElementException();
        E element = (E)elementData[front];
        front = (front + 1) % elementData.length;
        return element;
    }
    
    private void grow(int capacity) {
        if (capacity == -1)
            throw new OutOfMemoryError();
        
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        if (newCapacity < capacity)
            newCapacity = capacity;
        if (front < tail) {
            // [front...tail]
            elementData = Arrays.copyOf(elementData, newCapacity);
        } else {
            // [...tail front...]
            Object[] tempData = new Object[newCapacity];
            int moveSize = oldCapacity - front;
            System.arraycopy(elementData, front, tempData, 0, moveSize);
            System.arraycopy(elementData, 0, tempData, moveSize, tail);
            elementData = tempData;
            tempData = null;
            front = 0;
            tail = oldCapacity - 1;
        }
        
    }
    
    // 获取但不移除此队列的头
    public E peek() {
        if (isEmpty())
            throw new NoSuchElementException();
        else 
            return (E)elementData[front];
    }
    
    public boolean isEmpty() {
        return front == tail;
    }
    
    public int size() {
        int capacity = elementData.length;
        return (tail - front + capacity) % capacity;
    }
        
    public static void main(String[] args) {
        QueueDemo<Integer> q = new QueueDemo<>(5);
        q.offer(1);
        q.offer(2);
        q.offer(3);
        q.offer(4);
        System.out.println(q.poll());
        System.out.println(q.poll());
        q.offer(5);
        q.offer(6);
        q.offer(7);
        q.offer(8);
        while (!q.isEmpty()) {
            System.out.print(q.peek() + " ");
            q.poll();
        }
        //q.poll();
    }    
}

Stack

哦 还是瞎写的

栈 先进后出 没什么好说的 都比较简单

package com.wenr.collection;

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

/**
 * @author wenr
 * 
 * 实现函数：
 * - E peek()
 * - E pop()
 * - void push(E)
 * - isEmpty()
 * - size()
 * 
 */
public class StackDemo<E> {
    private static final int DEFAULT_SIZE = 10;
    private int top;
    private Object[] data;
    
    public StackDemo() {
        this(DEFAULT_SIZE);
    }
    
    public StackDemo(int capacity) {
        data = new Object[capacity];
    }
    
    public E peek() {
        if (isEmpty())
            throw new NoSuchElementException();
        return (E)data[top - 1];
    }
    
    public E pop() {
        if (isEmpty())
            throw new NoSuchElementException();
        return (E)data[--top];
    }
    
    public void push(E e) {
        int capacity = data.length; 
        if (top == capacity) {
            grow(capacity + 1);
        }
        data[top++] = e;
    }

    private void grow(int capacity) {
        if (capacity <= 0)
            throw new OutOfMemoryError();
        int oldCapacity = data.length;
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        if (newCapacity < capacity) {
            newCapacity = capacity;
        }
        data = Arrays.copyOf(data, newCapacity);
    }

    public boolean isEmpty() {
        return top == 0;
    }
    
    public int size() {
        return top;
    }
    
    public static void main(String[] args) {
        StackDemo<Integer> stack = new StackDemo<>(3);
        stack.push(1);
        stack.push(2);
        stack.push(3);
        stack.push(4);
        stack.push(5);
        stack.push(6);
        stack.pop();
        stack.push(7);
        while (!stack.isEmpty()) {
            System.out.println(stack.peek());
            stack.pop();
        }
    }
    
}