概述
This class implements the Set interface, backed by a hash table (actually a HashMap instance). It makes no guarantees as to the iteration order of the set; in particular, it does not guarantee that the order will remain constant over time. This class permits the null element.This class implements the Set interface, backed by a hash table (actually a HashMap instance). It makes no guarantees as to the iteration order of the set; in particular, it does not guarantee that the order will remain constant over time. This class permits the null element.
HashSet是基于HashMap來實(shí)現(xiàn)的，操作很簡(jiǎn)單，更像是對(duì)HashMap做了一次“封裝”，而且只使用了HashMap的key來實(shí)現(xiàn)各種特性，我們先來感性的認(rèn)識(shí)一下這個(gè)結(jié)構(gòu)：
HashSet set = new HashSet();set.add("語文");set.add("數(shù)學(xué)");set.add("英語");set.add("歷史");set.add("政治");set.add("地理");set.add("生物");set.add("化學(xué)");其大致的結(jié)構(gòu)是這樣的：
private transient HashMap map;// Dummy value to associate with an Object in the backing Mapprivate static final Object PRESENT = new Object();
map是整個(gè)HashSet的核心，而PRESENT則是用來造一個(gè)假的value來用的。Map有鍵和值，HashSet相當(dāng)于只有鍵，值都是相同的固定值，即PRESENT。
2. 基本操作
public boolean add(E e) { return map.put(e, PRESENT)==null;}public boolean remove(Object o) { return map.remove(o)==PRESENT;}public boolean contains(Object o) { return map.containsKey(o);}public int size() { return map.size();}基本操作也非常簡(jiǎn)單，就是調(diào)用HashMap的相關(guān)方法，其中value就是之前那個(gè)dummy的Object。
以上就是長(zhǎng)沙達(dá)內(nèi)教育java培訓(xùn)機(jī)構(gòu)的小編針對(duì)“Java hashset實(shí)現(xiàn)原理及工作原理”的內(nèi)容進(jìn)行的回答，希望對(duì)大家有所幫助，如有疑問，請(qǐng)?jiān)诰€咨詢，有專業(yè)老師隨時(shí)為你服務(wù)。
