JDK源码阅读(6)：HashSet类阅读笔记

HashSet

public class HashSet<E>
    extends AbstractSet<E>
    implements Set<E>, Cloneable, java.io.Serializable
{
    ...
}

1. map属性和构造方法

HashSet中最重要的属性是一个HashMap，在构造方法中会创建它。

private transient HashMap<E,Object> map;

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);
}

2. 业务方法-借助map

public Iterator<E> iterator() {
    return map.keySet().iterator();
}

public int size() {
    return map.size();
}

public boolean isEmpty() {
    return map.isEmpty();
}

public boolean contains(Object o) {
    return map.containsKey(o);
}

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

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

public void clear() {
    map.clear();
}