HashSet源码

签名

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

原理

构造方法

    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);
    }

// 这里留一个伏笔！
    HashSet(int initialCapacity, float loadFactor, boolean dummy) {
        map = new LinkedHashMap<>(initialCapacity, loadFactor);
    }

add

private static final Object PRESENT = new Object();

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

remove

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

LinkedHashSet源码

签名

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

原理

继承自HashSet
底层实现是LinkedHashMap，一些基本方法使用的父类HashSet的方法！
他的方法特别少，刚看我一度怀疑是我源码出问题了？？

在调了一个add方法之后我发现，好家伙，写的真好！

源码

    public LinkedHashSet(int initialCapacity, float loadFactor) {
        super(initialCapacity, loadFactor, true);
    }
    public LinkedHashSet(int initialCapacity) {
        super(initialCapacity, .75f, true);
    }
    public LinkedHashSet() {
        super(16, .75f, true);
    }
    public LinkedHashSet(Collection<? extends E> c) {
        super(Math.max(2*c.size(), 11), .75f, true);
        addAll(c);
    }

仔细看这几个构造方法，他们无一例外全部调用的都是HashSet的构造方法HashSet(int initialCapacity, float loadFactor, boolean dummy)

这里写的很鸡贼，我都没注意观察，看注释，他说这个包私有构造方法仅仅被LinkedHashSet使用！！

    /**
     * Constructs a new, empty linked hash set.  (This package private
     * constructor is only used by LinkedHashSet.) The backing
     * HashMap instance is a LinkedHashMap with the specified initial
     * capacity and the specified load factor.
     *
     * @param      initialCapacity   the initial capacity of the hash map
     * @param      loadFactor        the load factor of the hash map
     * @param      dummy             ignored (distinguishes this
     *             constructor from other int, float constructor.)
     * @throws     IllegalArgumentException if the initial capacity is less
     *             than zero, or if the load factor is nonpositive
     */
    HashSet(int initialCapacity, float loadFactor, boolean dummy) {
        map = new LinkedHashMap<>(initialCapacity, loadFactor);
    }