集合

一.集合框架

1.1 List

链表主要分为两种ArrayList,LinkedList

1.1.1 ArrayList

ArrayList组成是由数组形式生成的.故其拥有查找时速度快.但是插入和删除时的损耗较大
如果添加元素的数量大于其容量时.会触发扩容

  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);
    }

1.1.2 LinkedList

LinkedList是由双向链表组成,其在添加和删除时速度快.但是查找速度慢.

1.2 Set

集合主要分为HashSet,EnumSet,TreeSet

1.2.1 HashSet

HashSet是将其值进行哈希从而进行进行插入的.默认容量值为4.扩容增长为2的幂次.当其装填因子大于0.75将自动扩容
其

private static final Object PRESENT = new Object();
public HashSet() {
        map = new HashMap<>();
    }
public boolean add(E e) {
        return map.put(e, PRESENT)==null;
    }

1.2.2TreeSet

TreeSet是个有序集合.通过红黑树实现.如果需要对数据进行排序 最好选TreeSet,如果不需要 则是以HashSet

 private static final Object PRESENT = new Object();
public TreeSet() {
        this(new TreeMap<E,Object>());
    }
public boolean add(E e) {
        return m.put(e, PRESENT)==null;
    }

1.3 Map

映射主要分为HashMap,TreeMap

1.3.1 HashMap

HashMap主要对键进行散列.

static final int DEFAULT_INITIAL_CAPACITY = 4; //默认容量
static final int MAXIMUM_CAPACITY = 1 << 30;  //最大容量为2^30
static final float DEFAULT_LOAD_FACTOR = 0.75f; //装载因子
   public HashMap(int initialCapacity, float loadFactor) {
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal initial capacity: " +
                                               initialCapacity);
        if (initialCapacity > MAXIMUM_CAPACITY) {
            initialCapacity = MAXIMUM_CAPACITY;
        } else if (initialCapacity < DEFAULT_INITIAL_CAPACITY) {
            initialCapacity = DEFAULT_INITIAL_CAPACITY;
        }

        if (loadFactor <= 0 || Float.isNaN(loadFactor))
            throw new IllegalArgumentException("Illegal load factor: " +
                                               loadFactor);
        // Android-Note: We always use the default load factor of 0.75f.

        // This might appear wrong but it's just awkward design. We always call
        // inflateTable() when table == EMPTY_TABLE. That method will take "threshold"
        // to mean "capacity" and then replace it with the real threshold (i.e, multiplied with
        // the load factor).
        threshold = initialCapacity;
        init();
    }

1.3.2TreeMap

TreeMap采用红黑树的形式进行key,value值的插入.在插入同时会进行排序.