interface Collection {    ...}

interface Set extends Collection {    ...}

class HashSet implements  {    private static final Object PRESENT = new Object();    private transient HashMap
      
        ;        public HashSet() {        map = new HashMap<>();    }        public boolean add(E e) { //e=hello,world        return .put(e, PRESENT)==null;    }}
      

class  implements Map {    public V put(K key, V value) { //key=e=hello,world            //看哈希表是否为空，如果空，就开辟空间        if (table == EMPTY_TABLE) {            inflateTable(threshold);        }                //判断对象是否为null        if (key == null)            return putForNullKey(value);                int hash = (key); //和对象的hashCode()方法相关                //在哈希表中查找hash值        int i = indexFor(hash, table.length);        for (Entry
      
        e = table[i]; e != null; e = e.next) {            //这次的e其实是第一次的world            Object k;            if (e.hash == hash && ((k = e.key) == key || key.(k))) {                V oldValue = e.value;                e.value = value;                e.recordAccess(this);                return oldValue;                //走这里其实是没有添加元素            }        }        modCount++;        addEntry(hash, key, value, i); //把元素添加        return null;    }        transient int hashSeed = 0;        final int (Object k) { //k=key=e=hello,        int h = hashSeed;        if (0 != h && k instanceof String) {            return sun.misc.Hashing.stringHash32((String) k);        }        h ^= k.(); //这里调用的是对象的hashCode()方法        // This function ensures that hashCodes that differ only by        // constant multiples at each bit position have a bounded        // number of collisions (approximately 8 at default load factor).        h ^= (h >>> 20) ^ (h >>> 12);        return h ^ (h >>> 7) ^ (h >>> 4);    }}
      

//对应源码

addEntry(hash, key, value, i);

//

把元素添加

void addEntry(int hash, K key, V value, int bucketIndex) {    Entry
      
        e = table[bucketIndex];        table[bucketIndex] = new Entry
       
        (hash, key, value, e);        if (size++ >= threshold)            resize(2 * table.length);    }
       
      

1. hs.add("hello"

);//由于table里面没有，直接进addEntry

hs.add("world"

);//同上

hs.add("java"

);//同上

hs.add("world");//table里已经存在，(hash和equals相等),则在put()时，用新值替代老值。ps:这里的老值和新值都是world。

总结：