소스 코드 읽 기-Array List 의 내 면 세계 로 들 어가 기

public ArrayList() {
        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
    }

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);
        }
    }

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;
        }
    }

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

    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);
    }

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

    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);
    }

     /**
     * Increases the capacity to ensure that it can hold at least the
     * number of elements specified by the minimum capacity argument.
     *
     * @param minCapacity the desired minimum capacity
     */
    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);
    }

//ArrayList    remove  
    /**
     * Removes the element at the specified position in this list.
     * Shifts any subsequent elements to the left (subtracts one from their
     * indices).
     *
     * @param index the index of the element to be removed
     * @return the element that was removed from the list
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public E remove(int index) {
        rangeCheck(index);

        modCount++;
        E oldValue = elementData(index);

        int numMoved = size - index - 1;
        if (numMoved > 0)
            System.arraycopy(elementData, index+1, elementData, index,
                             numMoved);
        elementData[--size] = null; // clear to let GC do its work

        return oldValue;
    }

    /**
     * Removes the first occurrence of the specified element from this list,
     * if it is present.  If the list does not contain the element, it is
     * unchanged.  More formally, removes the element with the lowest index
     * i such that
     * (o==null ? get(i)==null : o.equals(get(i)))
     * (if such an element exists).  Returns true if this list
     * contained the specified element (or equivalently, if this list
     * changed as a result of the call).
     *
     * @param o element to be removed from this list, if present
     * @return true if this list contained the specified element
     */
    public boolean remove(Object o) {
        if (o == null) {
            for (int index = 0; index < size; index++)
                if (elementData[index] == null) {
                    fastRemove(index);
                    return true;
                }
        } else {
            for (int index = 0; index < size; index++)
                if (o.equals(elementData[index])) {
                    fastRemove(index);
                    return true;
                }
        }
        return false;
    }

    /*
     * Private remove method that skips bounds checking and does not
     * return the value removed.
     */
    private void fastRemove(int index) {
        modCount++;
        int numMoved = size - index - 1;
        if (numMoved > 0)
            System.arraycopy(elementData, index+1, elementData, index,
                             numMoved);
        elementData[--size] = null; // clear to let GC do its work
    }

    /**
     * Returns the element at the specified position in this list.
     *
     * @param  index index of the element to return
     * @return the element at the specified position in this list
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public E get(int index) {
        rangeCheck(index);

        return elementData(index);
    }

    /**
     * Checks if the given index is in range.  If not, throws an appropriate
     * runtime exception.  This method does *not* check if the index is
     * negative: It is always used immediately prior to an array access,
     * which throws an ArrayIndexOutOfBoundsException if index is negative.
     */
    private void rangeCheck(int index) {
        if (index >= size)
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }
 
    /**
     * Returns the index of the first occurrence of the specified element
     * in this list, or -1 if this list does not contain the element.
     * More formally, returns the lowest index i such that
     * (o==null ? get(i)==null : o.equals(get(i))),
     * or -1 if there is no such index.
     */
    public int indexOf(Object o) {
        if (o == null) {
            for (int i = 0; i < size; i++)
                if (elementData[i]==null)
                    return i;
        } else {
            for (int i = 0; i < size; i++)
                if (o.equals(elementData[i]))
                    return i;
        }
        return -1;
    }

   /**
     * Replaces the element at the specified position in this list with
     * the specified element.
     *
     * @param index index of the element to replace
     * @param element element to be stored at the specified position
     * @return the element previously at the specified position
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public E set(int index, E element) {
        rangeCheck(index);

        E oldValue = elementData(index);
        elementData[index] = element;
        return oldValue;
    }

ArrayList list = new ArrayList<>();
list.add("a");
list.add("b");
list.add("c");

//  for
for(String str : list){
    System.out.print(str + " ");
}

//     
Iterator it = list.iterator();
while(it.hasNext()){
    String str = it.next();
    System.out.print(str+" ");
}

//  foreach
for(String str : list){
    System.out.print(str + " ");
}

//    ListIterator
ListIterator listIt = list.listIterator();

//    
while(listIt.hasNext()){
    System.out.print(listIt.next()+" ");//a b c
}
//     ,             ，             ，           
while(listIt.hasPrevious()){
    System.out.print(listIt.previous()+" ");//c b a
}

    /**
     * Trims the capacity of this ArrayList instance to be the
     * list's current size.  An application can use this operation to minimize
     * the storage of an ArrayList instance.
     */
    public void trimToSize() {
        modCount++;
        if (size < elementData.length) {
            elementData = (size == 0)
              ? EMPTY_ELEMENTDATA
              : Arrays.copyOf(elementData, size);
        }
    }

//ArrayList   
public static void main(String[] args) {
		//             list，list    String     
        ArrayList list = new ArrayList();

        //      list   
        list.add("Item1");
        list.add("Item2");
        list.add(2, "Item3"); //        “Item3”      list  3   。
        list.add("Item4");

        //           
        System.out.println("The arraylist contains the following elements: "
                + list);

        //        
        int pos = list.indexOf("Item2");
        System.out.println("The index of Item2 is: " + pos);

        //           
        boolean check = list.isEmpty();
        System.out.println("Checking if the arraylist is empty: " + check);

        //        
        int size = list.size();
        System.out.println("The size of the list is: " + size);

        //               
        boolean element = list.contains("Item5");
        System.out
                .println("Checking if the arraylist contains the object Item5: "
                        + element);

        //           
        String item = list.get(0);
        System.out.println("The item is the index 0 is: " + item);

        //   arraylist    

        //  1   :                
        System.out
                .println("Retrieving items with loop using index and size list");
        for (int i = 0; i < list.size(); i++) {
            System.out.println("Index: " + i + " - Item: " + list.get(i));
        }

        //  2   :  foreach  
        System.out.println("Retrieving items using foreach loop");
        for (String str : list) {
            System.out.println("Item is: " + str);
        }

        //      :     
        // hasNext():   true           
        // next():        
        System.out.println("Retrieving items using iterator");
        for (Iterator it = list.iterator(); it.hasNext();) {
            System.out.println("Item is: " + it.next());
        }

        //     
        list.set(1, "NewItem");
        System.out.println("The arraylist after the replacement is: " + list);

        //     
        //    0       
        list.remove(0);

        //          "Item3"  
        list.remove("Item3");

        System.out.println("The final contents of the arraylist are: " + list);

        //    ArrayList   Array
        String[] simpleArray = list.toArray(new String[list.size()]);
        System.out.println("The array created after the conversion of our arraylist is: "
                        + Arrays.toString(simpleArray));
    }