HashSet的結(jié)構(gòu)
public class HashSet<E>
extends AbstractSet<E>
implements Set<E>, Cloneable, java.io.Serializable
{
static final long serialVersionUID = -5024744406713321676L;
private transient HashMap<E,Object> map;
// Dummy value to associate with an Object in the backing Map
private static final Object PRESENT = new Object();
}
????HastSet的底層存儲結(jié)構(gòu)是一個名字叫做map的HashMap躺屁，因為HashSet是單值的，非鍵值對蹈集，把HashSet的值用作了HashMap的Key烁试，Value就是上面代碼中的PRESENT。
構(gòu)造函數(shù)
public HashSet() {
map = new HashMap<>();
}
public HashSet(Collection<? extends E> c) {
map = new HashMap<>(Math.max((int) (c.size()/.75f) + 1, 16));
addAll(c);
}
public HashSet(int initialCapacity, float loadFactor) {
map = new HashMap<>(initialCapacity, loadFactor);
}
public HashSet(int initialCapacity) {
map = new HashMap<>(initialCapacity);
}
常用API
????如果元素e不存在Set當中拢肆，那么加入元素e减响，并返回true，否則返回false
public boolean add(E e) {
return map.put(e, PRESENT)==null;
}
????如果此集合包含指定的元素則返回true郭怪，否則返回false
public boolean contains(Object o) {
return map.containsKey(o);
}
????在Set中刪除元素o支示，如果刪除成功返回true，否則返回false
public boolean remove(Object o) {
return map.remove(o)==PRESENT;
}
