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

public boolean add(E e) {
	// size為當(dāng)前數(shù)據(jù)存放元素的數(shù)量
    ensureCapacityInternal(size + 1);
    // elementData為ArrayList內(nèi)部存放數(shù)據(jù)的數(shù)組
    elementData[size++] = e;  
    return true;
}
private void ensureCapacityInternal(int minCapacity) { 
	// 判斷數(shù)組是否為空，為空則將最小容量設(shè)置為默認(rèn)值10
    if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {  
        minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);  
    }  
	// 判斷當(dāng)前容量是否滿足最小容量
    ensureExplicitCapacity(minCapacity);  
}
private void ensureExplicitCapacity(int minCapacity) {
	// modCount用于記錄修改次數(shù)，作用于fast-fail機(jī)制
	// 如果在迭代的時(shí)候發(fā)現(xiàn)modCount被修改了，則會(huì)拋出異常來(lái)避免可能會(huì)出現(xiàn)的不確定行為
    modCount++;  
    // 如果當(dāng)前容量小于最小容量，則進(jìn)行擴(kuò)容
    if (minCapacity - elementData.length > 0)  
        grow(minCapacity);  
}
private void grow(int minCapacity) {  
    int oldCapacity = elementData.length;  
    // 計(jì)算新的容量，擴(kuò)大為原容量的1.5倍, oldCapacity >> 1 運(yùn)算表示右移一位，也就是相當(dāng)于除以二并取整
    int newCapacity = oldCapacity + (oldCapacity >> 1);
    if (newCapacity - minCapacity < 0)  
        newCapacity = minCapacity; 
    // 如果新容量超過(guò)了數(shù)組的最大容量,調(diào)用hugeCapacity方法來(lái)獲取一個(gè)更大的容量
    if (newCapacity - MAX_ARRAY_SIZE > 0)  
        newCapacity = hugeCapacity(minCapacity);  
    // 拷貝原數(shù)組，將原數(shù)組的元素復(fù)制到新數(shù)組中 
    elementData = Arrays.copyOf(elementData, newCapacity);  
}
private static int hugeCapacity(int minCapacity) {  
    if (minCapacity < 0) 
        throw new OutOfMemoryError();
	// 如果最小容量大于最大容量，則將容量設(shè)置為Integer.MAX_VALUE
    return (minCapacity > MAX_ARRAY_SIZE) ?  
        Integer.MAX_VALUE :  
        MAX_ARRAY_SIZE;  
}

public class Example1 {  
    public static void main(String[] args) {  
        ArrayList<String> list = new ArrayList<>(3);  
        list.add("qwe");  
        list.add("asd");  
        list.add("zxc");  
        Iterator<String> iterator = list.iterator();  
        while (iterator.hasNext()){  
            String next = iterator.next();  
            System.out.println(next);  
            list.remove(next);  
        }  
    }  
}
輸出：
qwe
Exception in thread "main" java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
	at java.util.ArrayList$Itr.next(ArrayList.java:851)
	at com.example.lepractice.collection.Example1.main(Example1.java:21)