AbstractSet 源代码

AbstractSet源代码

/* * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. * * * * * * * * * * * * * * * * * * * * */package java.util;/** * This class provides a skeletal implementation of the <tt>Set</tt> * interface to minimize the effort required to implement this * interface. <p> * * The process of implementing a set by extending this class is identical * to that of implementing a Collection by extending AbstractCollection, * except that all of the methods and constructors in subclasses of this * class must obey the additional constraints imposed by the <tt>Set</tt> * interface (for instance, the add method must not permit addition of * multiple instances of an object to a set).<p> * * Note that this class does not override any of the implementations from * the <tt>AbstractCollection</tt> class.  It merely adds implementations * for <tt>equals</tt> and <tt>hashCode</tt>.<p> * * This class is a member of the * <a href="{@docRoot}/../technotes/guides/collections/index.html"> * Java Collections Framework</a>. * * @param <E> the type of elements maintained by this set * * @author  Josh Bloch * @author  Neal Gafter * @see Collection * @see AbstractCollection * @see Set * @since 1.2 *//*此类提供 Set 接口的骨干实现，从而最大限度地减少了实现此接口所需的工作。通过扩展此类来实现一个 set 的过程与通过扩展 AbstractCollection 来实现 Collection 的过程是相同的，除了此类的子类中的所有方法和构造方法都必须服从 Set 接口所强加的额外限制（例如，add 方法必须不允许将一个对象的多个实例添加到一个 set 中）。注意，此类并没有重写 AbstractCollection 类中的任何实现。它仅仅添加了 equals 和 hashCode 的实现。 */public abstract class AbstractSet<E> extends AbstractCollection<E> implements Set<E> {    /**     * Sole constructor.  (For invocation by subclass constructors, typically     * implicit.)     */    protected AbstractSet() {    }    // Comparison and hashing    /**     * Compares the specified object with this set for equality.  Returns     * <tt>true</tt> if the given object is also a set, the two sets have     * the same size, and every member of the given set is contained in     * this set.  This ensures that the <tt>equals</tt> method works     * properly across different implementations of the <tt>Set</tt>     * interface.<p>     *     * This implementation first checks if the specified object is this     * set; if so it returns <tt>true</tt>.  Then, it checks if the     * specified object is a set whose size is identical to the size of     * this set; if not, it returns false.  If so, it returns     * <tt>containsAll((Collection) o)</tt>.     *     * @param o object to be compared for equality with this set     * @return <tt>true</tt> if the specified object is equal to this set     */    //实现了equals方法    public boolean equals(Object o) {        //先通过 == 对比，如果2个引用指向同一个对象，则返回 true        if (o == this)            return true;        //如果o不是Set类的对象，则返回false        if (!(o instanceof Set))            return false;        //将o转为集合类        Collection<?> c = (Collection<?>) o;        //先对比容量，如果容量不相等，则返回 false        if (c.size() != size())            return false;        try {            //容量相同的前提下，调用containsAll(),如果返回true，则代表2个容器想等            return containsAll(c);        } catch (ClassCastException unused)   {            //有异常则返回 false            return false;        } catch (NullPointerException unused) {            return false;        }    }    /**     * Returns the hash code value for this set.  The hash code of a set is     * defined to be the sum of the hash codes of the elements in the set,     * where the hash code of a <tt>null</tt> element is defined to be zero.     * This ensures that <tt>s1.equals(s2)</tt> implies that     * <tt>s1.hashCode()==s2.hashCode()</tt> for any two sets <tt>s1</tt>     * and <tt>s2</tt>, as required by the general contract of     * {@link Object#hashCode}.     *     * <p>This implementation iterates over the set, calling the     * <tt>hashCode</tt> method on each element in the set, and adding up     * the results.     *     * @return the hash code value for this set     * @see Object#equals(Object)     * @see Set#equals(Object)     */    //实现了计算hashCode方法    public int hashCode() {        int h = 0;        //获取容器元素组成的迭代器        Iterator<E> i = iterator();        while (i.hasNext()) {            //循环每个元素，将每个元素的hashCode相加，得到容器的hashCode            E obj = i.next();            if (obj != null)                h += obj.hashCode();        }        return h;    }    /**     * Removes from this set all of its elements that are contained in the     * specified collection (optional operation).  If the specified     * collection is also a set, this operation effectively modifies this     * set so that its value is the <i>asymmetric set difference</i> of     * the two sets.     *     * <p>This implementation determines which is the smaller of this set     * and the specified collection, by invoking the <tt>size</tt>     * method on each.  If this set has fewer elements, then the     * implementation iterates over this set, checking each element     * returned by the iterator in turn to see if it is contained in     * the specified collection.  If it is so contained, it is removed     * from this set with the iterator's <tt>remove</tt> method.  If     * the specified collection has fewer elements, then the     * implementation iterates over the specified collection, removing     * from this set each element returned by the iterator, using this     * set's <tt>remove</tt> method.     *     * <p>Note that this implementation will throw an     * <tt>UnsupportedOperationException</tt> if the iterator returned by the     * <tt>iterator</tt> method does not implement the <tt>remove</tt> method.     *     * @param  c collection containing elements to be removed from this set     * @return <tt>true</tt> if this set changed as a result of the call     * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation     *         is not supported by this set     * @throws ClassCastException if the class of an element of this set     *         is incompatible with the specified collection     * (<a href="Collection.html#optional-restrictions">optional</a>)     * @throws NullPointerException if this set contains a null element and the     *         specified collection does not permit null elements     * (<a href="Collection.html#optional-restrictions">optional</a>),     *         or if the specified collection is null     * @see #remove(Object)     * @see #contains(Object)     */    //移除掉所有存在容器c中的元素    public boolean removeAll(Collection<?> c) {        //检测不为空        Objects.requireNonNull(c);        boolean modified = false;        //比较当前容器和c容器哪个容量小，用小的容器遍历        if (size() > c.size()) {            for (Iterator<?> i = c.iterator(); i.hasNext(); )                //一个一个元素移除                modified |= remove(i.next());        } else {            for (Iterator<?> i = iterator(); i.hasNext(); ) {                if (c.contains(i.next())) {                    //如果在c容器中存在，则移除                    i.remove();                    modified = true;                }            }        }        return modified;    }}