在java中ArrayList集合底层的扩容原理

public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable{ 

	
	private static final int DEFAULT_CAPACITY = 10;

	
	private static final Object[] EMPTY_ELEMENTDATA = {};

	
	private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};

	
	transient Object[] elementData; // non-private to simplify nested class access

	
	private int size; 
}

1. ArrayList 集合底层存在6个成员变量
	还有一个 private static final long serialVersionUID = 8683452581122892189L;  
	序列化使用, 目前针对于当前的操作过程当中, 暂时不会使用得到。

2. ArrayList 集合当中核心的两个成员变量
	A. 底层维护数组  		transient Object[] elementData;
	B. 存储的元素个数		private int size; 

public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable{ 

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

    
    public ArrayList(Collection<? extends E> c) {
        elementData = c.toArray();
        if ((size = elementData.length) != 0) { 
            if (elementData.getClass() != Object[].class)
                elementData = Arrays.copyOf(elementData, size, Object[].class);
        } else { 
            this.elementData = 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);
        }
    }
}

来自于 ArrayList 集合当中的方法：
	1. public boolean add(E e){ ... }
	2. private void add(E e, Object[] elementData, int s){ .... }
	3. private Object[] grow()
	4. private Object[] grow(int minCapacity)

来自于其他类当中的功能
	1. Arrays.copyOf(elementData, newCapacity);  表示来自于 数组工具类 Arrays 当中的 copyOf() 底层使用的是 System.arraycopy() 方法
	2. Math.max(DEFAULT_CAPACITY, minCapacity)   表示来自于 数学工具类 Math 当中的 max() 方法，比较两个数据最大值，取较大者，返回

public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable{ 

    
    public boolean add(E e) {
        modCount++;
        add(e, elementData, size);
        return true;
    }
	
	
	
    private void add(E e, Object[] elementData, int s) {
        if (s == elementData.length)
            elementData = grow();
        elementData[s] = e;
        size = s + 1;
    }
	
	
	
	private Object[] grow() {
        return grow(size + 1);
    }


    
    private Object[] grow(int minCapacity) {
        int oldCapacity = elementData.length;
        if (oldCapacity > 0 || elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
            int newCapacity = ArraysSupport.newLength(oldCapacity,
                    minCapacity - oldCapacity, 
                    oldCapacity >> 1           );
            return elementData = Arrays.copyOf(elementData, newCapacity);
        } else {
            return elementData = new Object[Math.max(DEFAULT_CAPACITY, minCapacity)];
        }
    }
}