Java基础数据结构及其实现原理（一）

Java基础数据结构

Java类库中的基础数据结构

关注的问题：

• 实现的方式 基础的数据结构
• 是否有序 是否为空 是否重复

1， List

ArrayList的实现原理

实现原理：数组，可扩容

基本的特点：

• 查询快
• 增删慢

//无参构造 默认容量是空
public ArrayList() {
        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
    }

private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
//有参构造
public ArrayList(int initialCapacity) {
        if (initialCapacity > 0) {
            this.elementData = new Object[initialCapacity];
        } else if (initialCapacity == 0) {
            this.elementData = EMPTY_ELEMENTDATA;
        } else {
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        }
    }

添加的实现 基本就是数组的实现方式

public boolean add(E e) {
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        elementData[size++] = e;
        return true;
    }
public void add(int index, E element) {
        rangeCheckForAdd(index);

        ensureCapacityInternal(size + 1);  // Increments modCount!!
        System.arraycopy(elementData, index, elementData, index + 1,
                         size - index);
        elementData[index] = element;
        size++;
    }
//主要是动态扩容的实现


    private static int calculateCapacity(Object[] elementData, int minCapacity) {
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
            return Math.max(DEFAULT_CAPACITY, minCapacity);
        }
        return minCapacity;
    }

    private void ensureCapacityInternal(int minCapacity) {
        ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
    }

    private void ensureExplicitCapacity(int minCapacity) {
        modCount++;

        // overflow-conscious code
        if (minCapacity - elementData.length > 0)
            grow(minCapacity);
    }


private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity + (oldCapacity >> 1);//每次扩容为原来的容量的一半
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        // minCapacity is usually close to size, so this is a win:
        elementData = Arrays.copyOf(elementData, newCapacity);
    }

删除的方式1. 指定元素删除2.指定坐标删除

//按照坐标删除
public E remove(int index) {
        rangeCheck(index);

        modCount++;
        E oldValue = elementData(index);

        int numMoved = size - index - 1;
        if (numMoved > 0)
            System.arraycopy(elementData, index+1, elementData, index,
                             numMoved);
        elementData[--size] = null; // clear to let GC do its work

        return oldValue;
    }

//指定元素删除
public boolean remove(Object o) {
        if (o == null) {
            for (int index = 0; index < size; index++)
                if (elementData[index] == null) {
                    fastRemove(index);
                    return true;
                }
        } else {
            for (int index = 0; index < size; index++)
                if (o.equals(elementData[index])) {
                    fastRemove(index);
                    return true;
                }
        }
        return false;
    }
//不检测下标直接删除
private void fastRemove(int index) {
        modCount++;
        int numMoved = size - index - 1;
        if (numMoved > 0)
            System.arraycopy(elementData, index+1, elementData, index,
                             numMoved);
        elementData[--size] = null; // clear to let GC do its work
    }

迭代器的使用

待补充

LinkedList的实现原理

实现原理：双向链表

LinkedList	添加元素	删除元素	查看元素
链表	add(),set()	remove()	get()
队列	offer()	poll()	peek()
栈	push()	pop()	-

插入方法：

public boolean add(E e) {
    linkLast(e);
    return true;
}
//添加新节点的方式 将新节点前驱-last 后继-null
void linkLast(E e) {
    final Node<E> l = last;
    //Node(Node<E> prev, E element, Node<E> next)
    final Node<E> newNode = new Node<>(l, e, null);
    last = newNode;
    
    //判断链表是否有元素 有的话添加链表关系
    if (l == null)
        first = newNode;
    else
        l.next = newNode;
    size++;
    modCount++;
}

//添加新节点的方式 前驱null 后继first
private void linkFirst(E e) {
    final Node<E> f = first;
    final Node<E> newNode = new Node<>(null, e, f);
    first = newNode;
    //判断链表是否有元素 有的话添加关系
    if (f == null)
        last = newNode;
    else
        f.prev = newNode;
    size++;
    modCount++;
}
//按照下标添加
public void add(int index, E element) {
    checkPositionIndex(index);

    if (index == size)
        linkLast(element);
    else
        //element要插入的节点
        //node(index)原来位置的节点
        linkBefore(element, node(index));
}
//添加指定节点 在succ前面添加节点
void linkBefore(E e, Node<E> succ) {
    // assert succ != null;
    final Node<E> pred = succ.prev;
    //Node(Node<E> prev, E element, Node<E> next)
    final Node<E> newNode = new Node<>(pred, e, succ);
    succ.prev = newNode;
    if (pred == null)
        first = newNode;
    else
        pred.next = newNode;
    size++;
    modCount++;
}

删除方法

//指定对象的删除方法
public boolean remove(Object o) {
    if (o == null) {
        for (Node<E> x = first; x != null; x = x.next) {
            if (x.item == null) {
                unlink(x);
                return true;
            }
        }
    } else {
        for (Node<E> x = first; x != null; x = x.next) {
            if (o.equals(x.item)) {
                unlink(x);
                return true;
            }
        }
    }
    return false;
}

//指定下标的删除方法

public E remove(int index) {
    checkElementIndex(index);
    return unlink(node(index));
}

//删除链表的操作
E unlink(Node<E> x) {
    // assert x != null;
    final E element = x.item;
    final Node<E> next = x.next;
    final Node<E> prev = x.prev;

    if (prev == null) {
        //说明是链表首位
        first = next;
    } else {
        //链表前驱更改
        //节点的前驱节点的后继指向节点的后继
        prev.next = next;
        x.prev = null;
    }

    if (next == null) {
        last = prev;
    } else {
        //链表后继更改
        //节点的后继节点的前驱指向节点的前驱
        next.prev = prev;
        x.next = null;
    }

    x.item = null;
    size--;
    modCount++;
    return element;
}


//获取index位置的元素节点
Node<E> node(int index) {
    // assert isElementIndex(index);
	//双向链表，当节点index比size的一半大，反向搜索；反向正向
    if (index < (size >> 1)) {
        Node<E> x = first;
        for (int i = 0; i < index; i++)
            x = x.next;
        return x;
    } else {
        Node<E> x = last;
        for (int i = size - 1; i > index; i--)
            x = x.prev;
        return x;
    }
}

//删除头节点的操作
private E unlinkFirst(Node<E> f) {
    // assert f == first && f != null;
    final E element = f.item;
    final Node<E> next = f.next;
    f.item = null;
    f.next = null; // help GC
    first = next;
    
    //关键
    if (next == null)
        last = null;
    else
        next.prev = null;
    size--;
    modCount++;
    return element;
}

查找方法

//查找下标
public E get(int index) {
    checkElementIndex(index);
    return node(index).item;
}
//查找