源码解读全文

HashSet

• Val放在Map的Key中

构造

• 底层是放在HashMap里的

private transient HashMap<E,Object> map;
public HashSet() {
    map = new HashMap<>();
}

• 带参构造，调用HashMap

public HashSet(int initialCapacity, float loadFactor) {
    map = new HashMap<>(initialCapacity, loadFactor);
}

add

• 调用map的put方法

public boolean add(E e) {
    //如果存在就返回false
    return map.put(e, PRESENT)==null;
}

• value为固定的

private static final Object PRESENT = new Object();

remove

• 同样调用map的remove方法

public boolean remove(Object o) {
    return map.remove(o)==PRESENT;
}

LinkedHashSet

• 底层调用LinkedHashMap

构造

• 实际通过这个构造初始化一个LinkedHashMap

public LinkedHashSet() {
    super(16, .75f, true);
}

HashSet(int initialCapacity, float loadFactor, boolean dummy) {
    map = new LinkedHashMap<>(initialCapacity, loadFactor);
}

TreeSet

构造

• 内部调用了TreeMap

//接口类，TreeMap也继承了该类
private transient NavigableMap<E,Object> m;
public TreeSet() {
    this(new TreeMap<E,Object>());
}

TreeSet(NavigableMap<E,Object> m) {
    this.m = m;
}

put

• 功能方法

public boolean add(E e) {
    return m.put(e, PRESENT)==null;
}

小结

• set其实就是内部组合了map
• key为值，value为Object对象