/** * Adds the specified element to this set if it is not already present. * More formally, adds the specified element e to this set if * this set contains no element e2 such that * (e==null ? e2==null : e.equals(e2)). * If this set already contains the element, the call leaves the set * unchanged and returns false. * * @param e element to be added to this set * @return true if this set did not already contain the specified * element */ public boolean add(E e) { return map.put(e, PRESENT)==null; }
向HashSet内部维护的map添加新元素 //HashMap代码
/** * Associates the specified value with the specified key in this map. * If the map previously contained a mapping for the key, the old * value is replaced. * * @param key key with which the specified value is to be associated * @param value value to be associated with the specified key * @return the previous value associated with key, or * null if there was no mapping for key. * (A null return can also indicate that the map * previously associated null with key.) */ public V put(K key, V value) { if (table == EMPTY_TABLE) { inflateTable(threshold); } if (key == null) return putForNullKey(value); int hash = hash(key); int i = indexFor(hash, table.length); for (Entry e = table[i]; e != null; e = e.next) { Object k; if (e.hash == hash && ((k = e.key) == key || key.equals(k))) { V oldValue = e.value; e.value = value; e.recordAccess(this); return oldValue; } } modCount++; addEntry(hash, key, value, i); return null; }
/** * Returns true if this set contains the specified element. * More formally, returns true if and only if this set * contains an element e such that * (o==null ? e==null : o.equals(e)). * * @param o element whose presence in this set is to be tested * @return true if this set contains the specified element */ public boolean contains(Object o) { return map.containsKey(o); }
//HashMap代码
/** * Returns true if this map contains a mapping for the * specified key. * * @param key The key whose presence in this map is to be tested * @return true if this map contains a mapping for the specified * key. */ public boolean containsKey(Object key) { return getEntry(key) != null; }
/** * Returns the entry associated with the specified key in the * HashMap. Returns null if the HashMap contains no mapping * for the key. */ final Entry getEntry(Object key) { if (size == 0) { return null; } int hash = (key == null) ? 0 : hash(key); for (Entry e = table[indexFor(hash, table.length)]; e != null; e = e.next) { Object k; if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) return e; } return null; }
public boolean contains(Object o) { Iterator it = iterator(); if (o==null) { while (it.hasNext()) if (it.next()==null) return true; } else { while (it.hasNext()) if (o.equals(it.next())) return true; } return false; }
我查了下源码,我觉得
HashSet
的Hash
这里有文章。1.首先看添加元素的过程
//HashSet代码
向
HashSet
内部维护的map
添加新元素//HashMap代码
可以看出会对
Element
做哈希,所以如果添加Foo(1)
的话,保存到HashSet
过程中也少不了这个环节的。再来看比较的情况
//HashSet代码
//HashMap代码
结论
插入
HashSet
容器时对元素做哈希,判断容器是否含有某个元素时也要对元素做哈希,他们比较的是元素的哈希值。equals的方法,但是值得注意的是二楼说的是String下的equals方法,因为String的equals方法是重写过的,如果题主希望通过contains方法对于一般Object的比较的话,还是得和String一样重写equals方法,确定何种规则
这个是
AbstractCollection
的实现,AbstractList
,AbstractSet
都是以此为父类实现的.