list和set集合

arraylist集合

list底层是数值，默认扩充1.5倍

源码分析：线程不安全

public boolean add(E e) {
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        elementData[size++] = e;
        return true;
    }

判断是否扩容，默认是10个数组大小，取最大的值，按照1.5倍扩容

private void ensureCapacityInternal(int minCapacity) {
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
            minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
        }

        ensureExplicitCapacity(minCapacity);
    }

    private void ensureExplicitCapacity(int minCapacity) {
        modCount++;

        // overflow-conscious code
        if (minCapacity - elementData.length > 0)
            grow(minCapacity);
    }

    private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        // minCapacity is usually close to size, so this is a win:
        elementData = Arrays.copyOf(elementData, newCapacity);
    }

linkedlist学习

linkedlist底层的双向链表和双端队列、node节点包括pre、next、element

linkedlist源码分析：

线程不安全的

 public boolean add(E e) {
        linkLast(e);
        return true;
    }

底层是一个双向链表结构

 node包含3个元素

 vector是线程安全的，默认扩充2倍

  public synchronized boolean add(E e) {
        modCount++;
        ensureCapacityHelper(elementCount + 1);
        elementData[elementCount++] = e;
        return true;
    }

按照2倍扩充数组

   private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity + ((capacityIncrement > 0) ?
                                         capacityIncrement : oldCapacity);
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        elementData = Arrays.copyOf(elementData, newCapacity);
    }

底层也是数组

 set集合

 hashmap集合

键值对可以为null，但是只能有一个，null键存放到数组为0的位置

   static final int hash(Object key) {
        int h;
        return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
    }

线程不安全的

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

加载因子默认是0.75，node数组默认16个，当达到临界值进行扩容(数组*0.75=12个)，当元素为·12的时候会进行预先扩容到32个数组长度

 

 

 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;
        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) { // existing mapping for key
                V oldValue = e.value;
                if (!onlyIfAbsent || oldValue == null)
                    e.value = value;
                afterNodeAccess(e);
                return oldValue;
            }
        }
        ++modCount;
        if (++size > threshold)
            resize();
        afterNodeInsertion(evict);
        return null;
    }

public static void main(String[] args) {
List<Integer> list=new ArrayList<>();
list.add(1);
list.add(0);
list.add(3);
list.add(0);
System.out.println(list);
Set<Integer> set=new HashSet<>();
set.add(1);
set.add(0);
set.add(3);
set.add(0);
System.out.println(set);

}

打印结构：

[1, 0, 3, 0]
[0, 1, 3]

结论：list是有序，重复的

          set是无序的，并且不重复。只能有一个null值

 

 参考学习：https://www.bilibili.com/video/BV1YA411T76k?p=28&spm_id_from=pageDriver