//需要賦值A(chǔ)rrayList一個int類型長度值
    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);
        }
    }
    //無參構(gòu)造
    public ArrayList() {
        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
    }
	//入?yún)⒗^承了Collection對象轉(zhuǎn)化為ArrayList
    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;
        }
    }

/**
* Shared empty array instance used for empty instances.
*/
private static final Object[] EMPTY_ELEMENTDATA = {};
    
public ArrayList(int initialCapacity) {
		//initialCapacity大于0的情況下，就去new一個Object類型、長度為initialCapacity的數(shù)組
        if (initialCapacity > 0) {
            this.elementData = new Object[initialCapacity];
        } else if (initialCapacity == 0) {
        //initialCapacity等于0的情況下，則生成已經(jīng)創(chuàng)造好的Object[]；
            this.elementData = EMPTY_ELEMENTDATA;
        } else {
        //initialCapacity小于0的情況下，直接拋異常
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        }
    }

 private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
    
    public ArrayList() {
    	//當(dāng)你沒有賦值初始長度時，同樣是去賦值已經(jīng)創(chuàng)造好的空數(shù)組，沒有長度值
        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
    }

 private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
    
    public boolean add(E e) {
    	//1、add的第一步先去調(diào)用ensureCapacityInternal方法傳入size+1
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        elementData[size++] = e;
        return true;
    }
    
    //3、傳入一開始我們new的數(shù)組和add后的數(shù)組長度
    private static int calculateCapacity(Object[] elementData, int minCapacity) {
    	//如果elementData等于空數(shù)組，則對比DEFAULT_CAPACITY和minCapacity大小，返回大的值，DEFAULT_CAPACITY默認為10
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
            return Math.max(DEFAULT_CAPACITY, minCapacity);
        }
        //否則返回minCapacity
        return minCapacity;
    }

	//2、在ensureCapacityInternal方法內(nèi)部又去調(diào)用calculateCapacity(elementData, minCapacity)方法，傳入add數(shù)據(jù)后的list的size長度
    private void ensureCapacityInternal(int minCapacity) {
        ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
    }
	//4、拿到minCapacity的值后，對modCount++，比對添加后的list的長度和現(xiàn)在的list的長度來判斷是否需要進行擴容；
    private void ensureExplicitCapacity(int minCapacity) {
        modCount++;

        // 如果添加list的長度大于list現(xiàn)在的長度，則說明list的長度已經(jīng)不夠了，需要走grow(minCapacity)方法進行擴容
        if (minCapacity - elementData.length > 0)
            grow(minCapacity);
    }    

private void grow(int minCapacity) {
        // 拿到數(shù)組原來的長度
        int oldCapacity = elementData.length;
        //進行1.5倍計算
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        //如果1.5倍的值小于add后的長度值，則把add后的長度值設(shè)置成新數(shù)組的長度
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        //如果1.5倍的值大于array的最大長度則調(diào)用hugeCapacity(minCapacity)方法
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        // 調(diào)用Arrays.copyOf方法傳入舊數(shù)組對象和新數(shù)組的長度，進行擴容
        elementData = Arrays.copyOf(elementData, newCapacity);
    }
    
    private static int hugeCapacity(int minCapacity) {
        if (minCapacity < 0) // overflow
            throw new OutOfMemoryError();
            //如果add后的長度大于array的最大長度那就返回Integer的最大長度，否則返回array的最大長度，丟棄1.5倍的值，選擇array的最大長度來進行擴容
        return (minCapacity > MAX_ARRAY_SIZE) ?
            Integer.MAX_VALUE :
            MAX_ARRAY_SIZE;
    }