Source Reading List collection

A: Overview:

　　Mainly on the three collections

　　1.ArrayList:

　　　The bottom is an array, thread safe;

　　2.LinkedList:

　　　The bottom layer is a linked list, the thread unsafe;

　　3.Vector

　　   Underlying data structure is an array. Thread-safe;

Two: ArrayList resolved

　　

　　First, let's look at the ArrayList properties:

　　　　/ **
　　　　. * The Default Initial Capacity
　　　　* /
　　　　Private Final static int DEFAULT_CAPACITY = 10; // initial capacity value

  
  / ** 
     * Used for instance the Shared empty empty Array instances. 
     * / 
    Private  static  Final Object [] EMPTY_ELEMENTDATA = {}; // 0 specified, returns the empty capacity of ArrayList array

     / ** 
     * Used for instance the Shared empty Array . We instances default sized empty 
     * distinguish from EMPTY_ELEMENTDATA to know the this How much to the inflate When 
     * First Element iS added. 
     * / 
    Private  static  Final Object [] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {}; // with the distinguishing attributes are: the array is return to the default, and the capacity is designated attribute is zero return

     / ** 
     * Array of the Elements of Buffer the INTO Which are the ArrayList the Stored. 
     * iS of the capacity of the ArrayList the length of the this Array the Buffer. the Any
     * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
     * will be expanded to DEFAULT_CAPACITY when the first element is added.
     */
    transient Object[] elementData; // non-private to simplify nested class access//第一次保存元素时，数组将会扩容

    /**
     * The size of the ArrayList (the number of elements it contains).
     *
     * @serial
     */
    private int size;//ArrayList的实际大小

　　According to the above we can clearly find: ArrayList bottom is actually an array, ArrayList expansion have such a concept, precisely because it is expansion, so it can achieve "dynamic" growth

Constructor 1.2

    /**
     * Constructs an empty list with the specified initial capacity.
     *
     * @param  initialCapacity  the initial capacity of the list
     * @throws IllegalArgumentException if the specified initial capacity
     *         is negative
     */
　　//指定初始化长度initCapacity
    public ArrayList(int initialCapacity) {
        if (initialCapacity > 0) {
            this.elementData = new Object[initialCapacity];
        } else if (initialCapacity == 0) {
            this.elementData = EMPTY_ELEMENTDATA;
        } else {
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        }
    }

    /**
     * Constructs an empty list with an initial capacity of ten.
     */
　　//否则返回的是：DEFAULTCAPACITY_EMPTY_ELEMENTDATA
    public ArrayList() {
        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
    }

    /**
     * Constructs a list containing the elements of the specified
     * collection, in the order they are returned by the collection's
     * iterator.
     *
     * @param c the collection whose elements are to be placed into this list
     * @throws NullPointerException if the specified collection is null
     */
    public ArrayList(Collection<? extends E> c) {
        elementData = c.toArray();
        if ((size = elementData.length) != 0) {
            // c.toArray might (incorrectly) not return Object[] (see 6260652)
            if (elementData.getClass() != Object[].class)
                elementData = Arrays.copyOf(elementData, size, Object[].class);
        } else {
            // replace with empty array.
            this.elementData = EMPTY_ELEMENTDATA;
        }
    }

 

1.3 Add () method

Source as follows:

    /**
     * Appends the specified element to the end of this list.
     *
     * @param e element to be appended to this list
     * @return <tt>true</tt> (as specified by {@link Collection#add})
     */
    public boolean add(E e) {
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        elementData[size++] = e;
        return true;
    }

    /**
     * Inserts the specified element at the specified position in this
     * list. Shifts the element currently at that position (if any) and
     * any subsequent elements to the right (adds one to their indices).
     *
     * @param index index at which the specified element is to be inserted
     * @param element element to be inserted
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public void add(int index, E element) {
        rangeCheckForAdd(index);

        ensureCapacityInternal(size + 1);  // Increments modCount!!
        System.arraycopy(elementData, index, elementData, index + 1,
                         size - index);
        elementData[index] = element;
        size++;
    }

 

1.3.1 Add (E)

step:

• Check if the capacity is needed
• Insert elements

First, let's take a look at this method:

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

This method is very short, we can guess the name of the method is what he did:

• Confirmed list capacity, capacity plus one try, to see whether the necessary
• Adding elements

Next we look at the small capacity (+1) meets our needs:

To be continued