java(HashSet TreeSet源码分析)

hashSet 特点：基于Hash表实现，元素唯一不可重复（重写hashCode和equal方法）

TreeSet 特点：基于红黑树（平衡二叉树），元素唯一且有序

源码分析：

HashSet hs = new HashSet();

hs.add("sss");

1--------------------------------------------------------创建对象

public HashSet() {
    map = new HashMap<>();
}

public HashSet(Collection 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);
}

hashSet底层是HashMap()管理。

2------------------------------------------------------------添加元素

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

private static final Object PRESENT = new Object();  常量对象

public V put(K key, V value) {
    return putVal(hash(key), key, value, false, true);
}

final V putVal(int hash, K key, V value, boolean onlyIfAbsent, boolean evict) {
    Node[] tab;
    Node p; 
    int n, i;
    if ((tab = table) == null || (n = tab.length) == 0)
        n = (tab = resize()).length;      //首次创建时会走这个流程
    if ((p = tab[i = (n - 1) & hash]) == null)
        tab[i] = newNode(hash, key, value, null);
    else {
        Node e; K k;
        if (p.hash == hash &&
            ((k = p.key) == key || (key != null && key.equals(k))))
            e = p;
        else if (p instanceof TreeNode)
            e = ((TreeNode)p).putTreeVal(this, tab, hash, key, value);
        else {
            for (int binCount = 0; ; ++binCount) {
                if ((e = p.next) == null) {
                    p.next = newNode(hash, key, value, null);
                    if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                        treeifyBin(tab, hash);
                    break;
                }
                if (e.hash == hash &&
                    ((k = e.key) == key || (key != null && key.equals(k))))
                    break;
                p = e;
            }
        }
        if (e != null) { 
            V oldValue = e.value;
            if (!onlyIfAbsent || oldValue == null)
                e.value = value;
            afterNodeAccess(e);
            return oldValue;
        }
    }
    ++modCount;
    if (++size > threshold)
        resize();
    afterNodeInsertion(evict);
    return null;
}

TreeSet ts = new TreeSet();

ts.add("sss");

1-------------------------------------------------------------创建对象

public TreeSet() {
    this(new TreeMap());
}

public TreeSet(Comparator comparator) {
    this(new TreeMap<>(comparator));
}

public TreeSet(Collection c) {
    this();
    addAll(c);
}

public TreeSet(SortedSet s) {
    this(s.comparator());
    addAll(s);
}

底层是TreeMap存储数据

2----------------------------------------------添加元素

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

public final V put(K key, V value) {
    if (!inRange(key))
        throw new IllegalArgumentException("key out of range");
    return m.put(key, value);
}

public V put(K key, V value) {
    TreeMapEntry t = root;
    if (t == null) {
        compare(key, key); // type (and possibly null) check

        root = new TreeMapEntry<>(key, value, null);
        size = 1;
        modCount++;
        return null;
    }
    int cmp;
    TreeMapEntry parent;
    // split comparator and comparable paths
    Comparator cpr = comparator;
    if (cpr != null) {//如果构造器中传递进来比较器，则走这边
        do {    //元素比较及保存逻辑
            parent = t;
            cmp = cpr.compare(key, t.key);
            if (cmp < 0)
                t = t.left;
            else if (cmp > 0)
                t = t.right;
            else
                return t.setValue(value);
        } while (t != null);
    }
    else {//否则，走这边
        if (key == null)
            throw new NullPointerException();
        @SuppressWarnings("unchecked")
            Comparable k = (Comparable) key;//添加的元素对象实现比较器
        do {   //元素比较及保存逻辑
            parent = t;
            cmp = k.compareTo(t.key);
            if (cmp < 0)
                t = t.left;
            else if (cmp > 0)
                t = t.right;
            else
                return t.setValue(value);
        } while (t != null);
    }
    TreeMapEntry e = new TreeMapEntry<>(key, value, parent);
    if (cmp < 0)
        parent.left = e;
    else
        parent.right = e;
    fixAfterInsertion(e);
    size++;
    modCount++;
    return null;
}

内部实现Comparator保证大小有序（平衡二叉树，大的放右边，小的放左边 ）

2种实现方式

2.1给set构造方法传一个比较器

public TreeMap(Comparator comparator) { this.comparator = comparator; }

2.2让存储的自定义数据实现Comparator接口重写comparto()方法

 

 

为了方便自己理解， 故做此笔记，如有问题，请多多指教。

此处推荐大牛的讲解，更清楚https://juejin.im/user/57890289a633bd00585c3999