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  • jdk源码阅读笔记-HashSet

      通过阅读源码发现,HashSet底层的实现源码其实就是调用HashMap的方法实现的,所以如果你阅读过HashMap或对HashMap比较熟悉的话,那么阅读HashSet就很轻松,也很容易理解了。我之前也写了一篇关于hashMap源码阅读的文章,可以点击这里查看。

      使用过HashSet的都清楚它保存的元素是不可以重复的,其实HashSet的元素都是保存在HashMap的key中的,而HashMap的key是没有重复的。

      构造函数

    /**
         * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has
         * the specified initial capacity and the specified load factor.
         *
         * @param      initialCapacity   the initial capacity of the hash map
         * @param      loadFactor        the load factor of the hash map
         * @throws     IllegalArgumentException if the initial capacity is less
         *             than zero, or if the load factor is nonpositive
         */
        public HashSet(int initialCapacity, float loadFactor) {
            map = new HashMap<>(initialCapacity, loadFactor);
        }

      HashSet的构造方法都是直接调用了HashMap的构造方法,HashSet有很多个构造方法全部都是直接调用了HashMap的构造方法。

      add方法

    /**
         * Adds the specified element to this set if it is not already present.
         * More formally, adds the specified element <tt>e</tt> to this set if
         * this set contains no element <tt>e2</tt> such that
         * <tt>(e==null&nbsp;?&nbsp;e2==null&nbsp;:&nbsp;e.equals(e2))</tt>.
         * If this set already contains the element, the call leaves the set
         * unchanged and returns <tt>false</tt>.
         *
         * @param e element to be added to this set
         * @return <tt>true</tt> if this set did not already contain the specified
         * element
         */
        public boolean add(E e) {
            return map.put(e, PRESENT)==null;
        }

      contains方法

     /**
         * Returns <tt>true</tt> if this set contains the specified element.
         * More formally, returns <tt>true</tt> if and only if this set
         * contains an element <tt>e</tt> such that
         * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
         *
         * @param o element whose presence in this set is to be tested
         * @return <tt>true</tt> if this set contains the specified element
         */
        public boolean contains(Object o) {
            return map.containsKey(o);
        }

      remove方法

     /**
         * Removes the specified element from this set if it is present.
         * More formally, removes an element <tt>e</tt> such that
         * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>,
         * if this set contains such an element.  Returns <tt>true</tt> if
         * this set contained the element (or equivalently, if this set
         * changed as a result of the call).  (This set will not contain the
         * element once the call returns.)
         *
         * @param o object to be removed from this set, if present
         * @return <tt>true</tt> if the set contained the specified element
         */
        public boolean remove(Object o) {
            return map.remove(o)==PRESENT;
        }

     其他的方法也都是直接调用HashMap的方法,所以在这里就不用贴出来了。

      1、只要弄懂HashMap就很容易明白HashSet了,可以参考这篇文章:jdk源码浅读-HashMap https://www.cnblogs.com/rainple/p/9927263.html

      2、我自己在看源码的时候也手写了HashMap、HashSet等数据结构的类,大家可以下载下来参考一下,有不懂或不理解的地方可以问我,如果有什么问题也随时欢迎骚扰。项目地址:https://github.com/rainple1860/MyCollection

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  • 原文地址:https://www.cnblogs.com/rainple/p/9933406.html
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