菜鸟谈——java集合之Collection关系图谱及源码解析

java集合框架之Collection

1.类图

List和Set都是接口，它们都继承自Collection。List是有序的队列，可以有重复的元素；set不能有重复的元素。

为了方便，抽象出了AbstractCollection类，让其他类继承，该类实现了Collection中的绝大部分方法。AbstractList、AbstractSet、AbstractQueue都继承自AbstractCollection。

Collection中有iterator()方法，作用是返回一个iterator接口，通过iterator迭代器遍历集合。ListIterator是List接口所特有的。

2.Collection

collection定义如下：

public interface Collection<E> extends Iterable<E>

Collection接口的所有子类都必须实现两种构造函数：不带参数的和参数为Collection的构造函数。带参数的构造函数可以用来转换Collection类型。

//Collection的Api
int size();
boolean isEmpty();
boolean contains(Object o);
Iterator iterator();
Object[] toArray();
 T[] toArray(T[] a);
boolean add(E e);
boolean remove(Object o);
boolean containsAll(Collection c);
boolean addAll(Collection c);
boolean removeAll(Collection c);
boolean retainAll(Collection c);
void clear();
boolean equals(Object o);
int hashCode();
/**
下面的函数从jdk1.8开始支持
@since 1.8
**/
default boolean removeIf(Predicatesuper E> filter) {
  Objects.requireNonNull(filter);
  boolean removed = false;
  final Iterator each = iterator();
  while (each.hasNext()) {
    if (filter.test(each.next())) {
      each.remove();
      removed = true;
    }
  }
  return removed;
}
@Override
default Spliterator spliterator() {
  return Spliterators.spliterator(this, 0);
}
default Stream stream() {
  return StreamSupport.stream(spliterator(), false);
}
default Stream parallelStream() {
  return StreamSupport.stream(spliterator(), true);
}

3.List

list代码实现

public interface List<E> extends Collection<E> {}

//Collection集合API
int size();
boolean isEmpty();
boolean contains(Object o);
Iterator iterator();
Object[] toArray();
 T[] toArray(T[] a);
boolean add(E e);
boolean remove(Object o);
boolean containsAll(Collection c);
boolean addAll(Collection c);
boolean removeAll(Collection c);
boolean retainAll(Collection c);
void clear();
boolean equals(Object o);
int hashCode();

//相比Collection，list新增的API
E get(int index); //获取指定位置的元素
E set(int index, E element); //修改指定位置的元素
void add(int index, E element); //添加元素到指定位置
boolean addAll(int index, Collection c);//在指定位置添加其他集合中的元素
E remove(int index);//删除指定位置的元素
int indexOf(Object o); //获取指定元素的索引
int lastIndexOf(Object o); //获取指定元素从右边的索引
ListIterator listIterator(); //获得Iterator
ListIterator listIterator(int index);
List subList(int fromIndex, int toIndex);//获取子List
/**
下面的函数从jdk1.8开始支持
@since 1.8
**/
default void replaceAll(UnaryOperator operator) {
  Objects.requireNonNull(operator);
  final ListIterator li = this.listIterator();
  while (li.hasNext()) {
    li.set(operator.apply(li.next()));
  }
}
@SuppressWarnings({"unchecked", "rawtypes"})
default void sort(Comparatorsuper E> c) {
  Object[] a = this.toArray();
  Arrays.sort(a, (Comparator) c);
  ListIterator i = this.listIterator();
  for (Object e : a) {
    i.next();
    i.set((E) e);
  }
}
@Override
default Spliterator spliterator() {
  return Spliterators.spliterator(this, Spliterator.ORDERED);
}

4.set

set实现代码

public interface Set<E> extends Collection<E>{}

set也继承自Collection接口，且里面不能有重复元素。关于API，set与Collection的API完全一样。。。

int size();
boolean isEmpty();
boolean contains(Object o);
Iterator iterator();
Object[] toArray();
 T[] toArray(T[] a);
boolean add(E e);
boolean remove(Object o);
boolean containsAll(Collection c);
boolean addAll(Collection c);
boolean retainAll(Collection c);
boolean removeAll(Collection c);
void clear();
boolean equals(Object o);
int hashCode();

@Override
default Spliterator spliterator() {
  return Spliterators.spliterator(this, Spliterator.DISTINCT);
}

5.AbstractCollection

AbstracCollection实现代码

public abstract class AbstractCollection<E> implements Collection<E> {}

AbstractCollection是一个抽象类，实现了collection中除了iterator()和size()之外的所有方法。

public abstract class AbstractCollection<E> implements Collection<E> {
    protected AbstractCollection() {
    }
//******Query Operations ********************//

    //iterator()和size()方法未实现
    public abstract Iterator iterator();
    public abstract int size();
    //判断集合是否为空  
    public boolean isEmpty() {
        return size() == 0; //判断集合大小是否为0
    }
    //检查集合中是否包含指定元素
    public boolean contains(Object o) {
        Iterator it = iterator();
        if (o==null) {//可以看出，任何非空集合都包含null
            while (it.hasNext())
                if (it.next()==null)
                    return true;
        } else {
            while (it.hasNext())
                if (o.equals(it.next()))
                    return true;
        }
        return false;
    }
    //将集合转变为数组
    public Object[] toArray() {
        // Estimate size of array; be prepared to see more or fewer elements
        Object[] r = new Object[size()]; //定义一个数组，大小为集合的大小
        Iterator it = iterator();
        for (int i = 0; i < r.length; i++) {
            if (! it.hasNext()) // fewer elements than expected
                return Arrays.copyOf(r, i);
            r[i] = it.next();
        }
        return it.hasNext() ? finishToArray(r, it) : r;
    }

    @SuppressWarnings("unchecked")
    public  T[] toArray(T[] a) {
        // Estimate size of array; be prepared to see more or fewer elements
        int size = size();
        T[] r = a.length >= size ? a :
                  (T[])java.lang.reflect.Array
                  .newInstance(a.getClass().getComponentType(), size);
        Iterator it = iterator();

        for (int i = 0; i < r.length; i++) {
            if (! it.hasNext()) { // fewer elements than expected
                if (a == r) {
                    r[i] = null; // null-terminate
                } else if (a.length < i) {
                    return Arrays.copyOf(r, i);
                } else {
                    System.arraycopy(r, 0, a, 0, i);
                    if (a.length > i) {
                        a[i] = null;
                    }
                }
                return a;
            }
            r[i] = (T)it.next();
        }
        // more elements than expected
        return it.hasNext() ? finishToArray(r, it) : r;
    }

    /**
     * The maximum size of array to allocate.
     * Some VMs reserve some header words in an array.
     * Attempts to allocate larger arrays may result in
     * OutOfMemoryError: Requested array size exceeds VM limit
     */
    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

    @SuppressWarnings("unchecked")
    private static  T[] finishToArray(T[] r, Iterator it) {
        int i = r.length;
        while (it.hasNext()) {
            int cap = r.length;
            if (i == cap) {
                int newCap = cap + (cap >> 1) + 1;
                // overflow-conscious code
                if (newCap - MAX_ARRAY_SIZE > 0)
                    newCap = hugeCapacity(cap + 1);
                r = Arrays.copyOf(r, newCap);
            }
            r[i++] = (T)it.next();
        }
        // trim if overallocated
        return (i == r.length) ? r : Arrays.copyOf(r, i);
    }

    private static int hugeCapacity(int minCapacity) {
        if (minCapacity < 0) // overflow
            throw new OutOfMemoryError
                ("Required array size too large");
        return (minCapacity > MAX_ARRAY_SIZE) ?
            Integer.MAX_VALUE :
            MAX_ARRAY_SIZE;
    }

//******Modification Operations ********************//
    public boolean add(E e) {
        throw new UnsupportedOperationException();
    }
    //删除对象o
    public boolean remove(Object o) {
        Iterator it = iterator();
        if (o==null) {
            while (it.hasNext()) {
                if (it.next()==null) {
                    it.remove();
                    return true;
                }
            }
        } else {
            while (it.hasNext()) {
                if (o.equals(it.next())) {
                    it.remove();
                    return true;
                }
            }
        }
        return false;
    }

//******Bulk Operations ********************//
    //判断是否包含集合C中的所有元素
    public boolean containsAll(Collection c) {
        for (Object e : c)
            if (!contains(e))
                return false;
        return true;
    }
    //添加集合C中所有元素
    public boolean addAll(Collection c) {
        boolean modified = false;
        for (E e : c)
            if (add(e))
                modified = true;
        return modified;
    }
    //删除集合c中所有元素
    public boolean removeAll(Collection c) {
        Objects.requireNonNull(c);
        boolean modified = false;
        Iterator it = iterator();
        while (it.hasNext()) {
            if (c.contains(it.next())) {
                it.remove();
                modified = true;
            }
        }
        return modified;
    }

    /**
     * {@inheritDoc}
     *
     * 
This implementation iterates over this collection, checking each
     * element returned by the iterator in turn to see if it's contained
     * in the specified collection.  If it's not so contained, it's removed
     * from this collection with the iterator's remove method.
     */
    //当前集合  指定集合C
    //这个接口遍历整个集合，检测每个元素是否在指定集合C中，如果不存在就调用remove方法删除
    //提示：两个集合的交集
    public boolean retainAll(Collection c) {
        Objects.requireNonNull(c);
        boolean modified = false;
        Iterator it = iterator();
        while (it.hasNext()) {
            if (!c.contains(it.next())) {
                it.remove();
                modified = true;
            }
        }
        return modified;
    }
    //清空集合
    public void clear() {
        Iterator it = iterator();
        while (it.hasNext()) {
            it.next();
            it.remove();
        }
    }

    //将集合元素显示为[String]
    //  String conversion
    public String toString() {
        Iterator it = iterator();
        if (! it.hasNext())
            return "[]";

        StringBuilder sb = new StringBuilder();
        sb.append('[');
        for (;;) {
            E e = it.next();
            sb.append(e == this ? "(this Collection)" : e);
            if (! it.hasNext())
                return sb.append(']').toString();
            sb.append(',').append(' ');
        }
    }
}

6.AbstractList

AbstractList代码实现

public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E> {}

package java.util;
public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E> {
    protected AbstractList() {
    }
    //**************下面几个方法会在子类中进行实现**********************************//
    public boolean add(E e) {
        add(size(), e);
        return true;
    }
    abstract public E get(int index);
    public E set(int index, E element) {
        throw new UnsupportedOperationException();
    }
    public void add(int index, E element) {
        throw new UnsupportedOperationException();
    }
    public E remove(int index) {
        throw new UnsupportedOperationException();
    }


    //***************Search Operations**************************************//
    //搜索对象O的索引
    public int indexOf(Object o) {
        ListIterator it = listIterator();
        if (o==null) {
            while (it.hasNext())
                if (it.next()==null)//执行it.next()，会先返回it指向位置的值，然后it会移到下一个位置
                    return it.previousIndex();//所以要返回it.previousIndex()
        } else {
            while (it.hasNext())
                if (o.equals(it.next()))
                    return it.previousIndex();
        }
        return -1;
    }
    //反向索引
    public int lastIndexOf(Object o) {
        ListIterator it = listIterator(size());
        if (o==null) {
            while (it.hasPrevious())
                if (it.previous()==null)
                    return it.nextIndex();
        } else {
            while (it.hasPrevious())
                if (o.equals(it.previous()))
                    return it.nextIndex();
        }
        return -1;
    }

    // Bulk Operations
    //清除集合 调用removeRange()函数移除指定位置的元素
    public void clear() {
        removeRange(0, size());
    }
    //给指定位置添加集合
    public boolean addAll(int index, Collection c) {
        rangeCheckForAdd(index);
        boolean modified = false;
        for (E e : c) {
            add(index++, e); //add()方法会在子类中实现
            modified = true;
        }
        return modified;
    }


    // Comparison and hashing
    public boolean equals(Object o) {
        if (o == this)
            return true;
        if (!(o instanceof List))
            return false;
        ListIterator e1 = listIterator();
        ListIterator e2 = ((List) o).listIterator();
        while (e1.hasNext() && e2.hasNext()) {
            E o1 = e1.next();
            Object o2 = e2.next();
            if (!(o1==null ? o2==null : o1.equals(o2)))
                return false;
        }
        return !(e1.hasNext() || e2.hasNext());
    }
    public int hashCode() {
        int hashCode = 1;
        for (E e : this)
            hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
        return hashCode;
    }
    //删除指定集合范围内的元素
    protected void removeRange(int fromIndex, int toIndex) {
        ListIterator it = listIterator(fromIndex);
        for (int i=0, n=toIndex-fromIndex; i//********************************迭代器*************************//
    public Iterator iterator() {
        return new Itr(); //内部类
    }
    public ListIterator listIterator() {
        return listIterator(0);
    }
    public ListIterator listIterator(final int index) {
        rangeCheckForAdd(index);
        return new ListItr(index);
    }
    private class Itr implements Iterator<E> {
        /**
         * Index of element to be returned by subsequent call to next.
         */
        int cursor = 0;

        /**
         * Index of element returned by most recent call to next or
         * previous.  Reset to -1 if this element is deleted by a call
         * to remove.
         */
        int lastRet = -1;

        /**
         * The modCount value that the iterator believes that the backing
         * List should have.  If this expectation is violated, the iterator
         * has detected concurrent modification.
         */
        int expectedModCount = modCount;
        public boolean hasNext() {
            return cursor != size();
        }
        public E next() {
            checkForComodification();
            try {
                int i = cursor;
                E next = get(i);
                lastRet = i;
                cursor = i + 1;
                return next;
            } catch (IndexOutOfBoundsException e) {
                checkForComodification();
                throw new NoSuchElementException();
            }
        }

        public void remove() {
            if (lastRet < 0)
                throw new IllegalStateException();
            checkForComodification();
            try {
                AbstractList.this.remove(lastRet);
                if (lastRet < cursor)
                    cursor--;
                lastRet = -1;
                expectedModCount = modCount;
            } catch (IndexOutOfBoundsException e) {
                throw new ConcurrentModificationException();
            }
        }

        final void checkForComodification() {
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
        }
    }

    private class ListItr extends Itr implements ListIterator<E> {
        ListItr(int index) {
            cursor = index;
        }

        public boolean hasPrevious() {
            return cursor != 0;
        }

        public E previous() {
            checkForComodification();
            try {
                int i = cursor - 1;
                E previous = get(i);
                lastRet = cursor = i;
                return previous;
            } catch (IndexOutOfBoundsException e) {
                checkForComodification();
                throw new NoSuchElementException();
            }
        }

        public int nextIndex() {
            return cursor;
        }

        public int previousIndex() {
            return cursor-1;
        }

        public void set(E e) {
            if (lastRet < 0)
                throw new IllegalStateException();
            checkForComodification();

            try {
                AbstractList.this.set(lastRet, e);
                expectedModCount = modCount;
            } catch (IndexOutOfBoundsException ex) {
                throw new ConcurrentModificationException();
            }
        }

        public void add(E e) {
            checkForComodification();

            try {
                int i = cursor;
                AbstractList.this.add(i, e);
                lastRet = -1;
                cursor = i + 1;
                expectedModCount = modCount;
            } catch (IndexOutOfBoundsException ex) {
                throw new ConcurrentModificationException();
            }
        }
    }
    public List subList(int fromIndex, int toIndex) {
        return (this instanceof RandomAccess ?
                new RandomAccessSubList<>(this, fromIndex, toIndex) :
                new SubList<>(this, fromIndex, toIndex));
    }


    /**
     * The number of times this list has been structurally modified.
     记录集合被修改次数
     */
    protected transient int modCount = 0;

    //添加元素之前，检测添加的索引是否合法
    private void rangeCheckForAdd(int index) {
        if (index < 0 || index > size())
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }
    //拼接索引越界消息
    private String outOfBoundsMsg(int index) {
        return "Index: "+index+", Size: "+size();
    }
}

//**************************子列表SubList***********************************//
class SubList extends AbstractList {
    private final AbstractList l;
    private final int offset;
    private int size;
    //当需要获取一个List时，底层并不是真正的返回一个子list 还是原来的list，
    //只不过在操作时，索引全部限定在用户所需的子List部分而已
    SubList(AbstractList list, int fromIndex, int toIndex) {
        if (fromIndex < 0)
            throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
        if (toIndex > list.size())
            throw new IndexOutOfBoundsException("toIndex = " + toIndex);
        if (fromIndex > toIndex)
            throw new IllegalArgumentException("fromIndex(" + fromIndex +
                                               ") > toIndex(" + toIndex + ")");
        l = list; //原封不动的将原来的list赋值给l
        offset = fromIndex; //偏移量
        size = toIndex - fromIndex; //子LIST的大小
        this.modCount = l.modCount;
    }
    //注：下面所有的操作都在索引上加偏移量offset，相当于在原来的list的副本上操作子List
    public E set(int index, E element) {
        rangeCheck(index);
        checkForComodification();
        return l.set(index+offset, element);
    }

    public E get(int index) {
        rangeCheck(index);
        checkForComodification();
        return l.get(index+offset);
    }

    public int size() {
        checkForComodification();
        return size;
    }

    public void add(int index, E element) {
        rangeCheckForAdd(index);
        checkForComodification();
        l.add(index+offset, element);
        this.modCount = l.modCount;
        size++;
    }

    public E remove(int index) {
        rangeCheck(index);
        checkForComodification();
        E result = l.remove(index+offset);
        this.modCount = l.modCount;
        size--;
        return result;
    }

    protected void removeRange(int fromIndex, int toIndex) {
        checkForComodification();
        l.removeRange(fromIndex+offset, toIndex+offset);
        this.modCount = l.modCount;
        size -= (toIndex-fromIndex);
    }

    public boolean addAll(Collection c) {
        return addAll(size, c);
    }

    public boolean addAll(int index, Collection c) {
        rangeCheckForAdd(index);
        int cSize = c.size();
        if (cSize==0)
            return false;

        checkForComodification();
        l.addAll(offset+index, c);
        this.modCount = l.modCount;
        size += cSize;
        return true;
    }

    public Iterator iterator() {
        return listIterator();
    }

    public ListIterator listIterator(final int index) {
        checkForComodification();
        rangeCheckForAdd(index);

        return new ListIterator() {
            private final ListIterator i = l.listIterator(index+offset);

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

            public E next() {
                if (hasNext())
                    return i.next();
                else
                    throw new NoSuchElementException();
            }

            public boolean hasPrevious() {
                return previousIndex() >= 0;
            }

            public E previous() {
                if (hasPrevious())
                    return i.previous();
                else
                    throw new NoSuchElementException();
            }

            public int nextIndex() {
                return i.nextIndex() - offset;
            }

            public int previousIndex() {
                return i.previousIndex() - offset;
            }

            public void remove() {
                i.remove();
                SubList.this.modCount = l.modCount;
                size--;
            }

            public void set(E e) {
                i.set(e);
            }

            public void add(E e) {
                i.add(e);
                SubList.this.modCount = l.modCount;
                size++;
            }
        };
    }

    public List subList(int fromIndex, int toIndex) {
        return new SubList<>(this, fromIndex, toIndex);
    }

    private void rangeCheck(int index) {
        if (index < 0 || index >= size)
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }

    private void rangeCheckForAdd(int index) {
        if (index < 0 || index > size)
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }

    private String outOfBoundsMsg(int index) {
        return "Index: "+index+", Size: "+size;
    }

    private void checkForComodification() {
        if (this.modCount != l.modCount)
            throw new ConcurrentModificationException();
    }
}

class RandomAccessSubList extends SubList implements RandomAccess {
    RandomAccessSubList(AbstractList list, int fromIndex, int toIndex) {
        super(list, fromIndex, toIndex);
    }

    public List subList(int fromIndex, int toIndex) {
        return new RandomAccessSubList<>(this, fromIndex, toIndex);
    }
}

7.AbstractSet

AbstractSet的定义如下：

public abstract class AbstractSet<E> extends AbstractCollection<E> implements Set<E> {}

和AbstractCollection一样

8.Iterator

public interface Iterator<E> {}

集合的迭代器，

API有：是否存在下一个元素、获取下一个元素、删除当前元素

注意：fail-fast机制

当某个线程A通过iterator去遍历某集合的过程中，若该集合的内容被其他线程改变了，那么线程A访问集合时，就会抛出CurrentModificationException异常，产生fail-fast事件

9.ListIterator

专门遍历list，提供前遍历和后遍历

注意

迭代器执行it.next()，会先返回it指向位置的值，然后it会移到下一个位置