java(HashSet TreeSet源碼分析)

hashSet 特點：基於Hash表實現，元素唯一不可重複（重寫hashCode和equal方法）

TreeSet 特點：基於紅黑樹（平衡二叉樹），元素唯一且有序

源碼分析：

HashSet hs = new HashSet();

hs.add("sss");

1--------------------------------------------------------創建對象

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);
}

hashSet底層是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();  常量對象

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<K,V>[] tab;
    Node<K,V> p; 
    int n, i;
    if ((tab = table) == null || (n = tab.length) == 0)
        n = (tab = resize()).length;      //首次創建時會走這個流程
    if ((p = tab[i = (n - 1) & hash]) == null)
        tab[i] = newNode(hash, key, value, null);
    else {
        Node<K,V> 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<K,V>)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-------------------------------------------------------------創建對象

public TreeSet() {
    this(new TreeMap<E,Object>());
}

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

public TreeSet(Collection<? extends E> c) {
    this();
    addAll(c);
}

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

底層是TreeMap存儲數據

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<K,V> 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<K,V> parent;
    // split comparator and comparable paths
    Comparator<? super K> cpr = comparator;
    if (cpr != null) {//如果構造器中傳遞進來比較器，則走這邊
        do {    //元素比較及保存邏輯
            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 {//否則，走這邊
        if (key == null)
            throw new NullPointerException();
        @SuppressWarnings("unchecked")
            Comparable<? super K> k = (Comparable<? super K>) key;//添加的元素對象實現比較器
        do {   //元素比較及保存邏輯
            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<K,V> e = new TreeMapEntry<>(key, value, parent);
    if (cmp < 0)
        parent.left = e;
    else
        parent.right = e;
    fixAfterInsertion(e);
    size++;
    modCount++;
    return null;
}

內部實現Comparator保證大小有序（平衡二叉樹，大的放右邊，小的放左邊 ）

2種實現方式

2.1給set構造方法傳一個比較器

public TreeMap(Comparator<? super K> comparator) { this.comparator = comparator; }

2.2讓存儲的自定義數據實現Comparator接口重寫comparto()方法

 

 

爲了方便自己理解， 故做此筆記，如有問題，請多多指教。