java集合框架源码分析
Java Collection FrameWork 源码分析（JDK8）
1.ArrayList
添加元素的方式和移除元素
add(E e)
add(int index,E element)
addAll(Collection c)
addAll(int index, Collection c)
remove(int index)
remove(Object o)
public boolean add(E e) {
//确保添加元素后的容器（数组.length）是否放得下，size为数组中元素个数,size+1是添加后元素个数
ensureCapacityInternal(size + 1); // Increments modCount!!
elementData[size++] = e;
return true;
}
private static final int DEFAULT_CAPACITY = 10;
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
private void ensureCapacityInternal(int minCapacity) {
ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
}
private static int calculateCapacity(Object[] elementData, int minCapacity) {
//如果数组elementData为空,说明现在数组还没被初始化，仅仅是有个引用
//那么minCapacity=size+1=1,空的数组没有办法存放元素，那么就将默认数组容量设为10并返回
//如果数组elementData不为空直接返回minCapacity
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
return Math.max(DEFAULT_CAPACITY, minCapacity);
}
return minCapacity;
}
private void ensureExplicitCapacity(int minCapacity) {
//List,map这些集合结构中常能看到modCount属性，在对集合进行新增或移除操作时会使modCount+1,这 //是一个记录集合变化次数的变量。作用是在使用迭代器Iterator对集合进行遍历时，用modCount来判断集 //合内数据没有发生变化，否则会抛出异常。
链接：https://www.jianshu.com/p/d01e9cf207f9
//判断是否需要扩容
// overflow-conscious code
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}
private void grow(int minCapacity) {
// overflow-conscious code
//将当前数组长度赋值为老数组容量
int oldCapacity = elementData.length;
//将老数组容量扩容1.5倍后赋值给新数组容量
int newCapacity = oldCapacity + (oldCapacity >> 1);
//这种情况出现的原因为如果返回的minCapacity==10，此时elementDate还为{}，没有被初始化，
//newCapacity==oldCapacity==00,int范围为-2^31~2^31-1
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);
}
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}
@SuppressWarnings("unchecked")
public static T[] copyOf(T[] original, int newLength) {
return (T[]) copyOf(original, newLength, original.getClass());
}
public static T[] copyOf(U[] original, int newLength, Class newType) {
@SuppressWarnings("unchecked")
T[] copy = ((Object)newType == (Object)Object[].class)
? (T[]) new Object[newLength]
: (T[]) Array.newInstance(newType.getComponentType(), newLength);
System.arraycopy(original, 0, copy, 0,
Math.min(original.length, newLength));
return copy;
}
//调用了本地方法arraycopy
/**
* @param src the source array.
* @param srcPos starting position in the source array.
* @param dest the destination array.
* @param destPos starting position in the destination data.
* @param length the number of array elements to be copied.
*\
把src数组从srcPos位置其长度为length复制到dest数组的destPos位置后
public static native void arraycopy(Object src, int srcPos,
Object dest, int destPos,
int length);
int[] arr = new int[100];
int[] arr2 = {11,12,23,23};
for (int i = 0; i <10 ; i++) {
arr[i]=i;
}
System.arraycopy(arr, 0, arr, 4, 10);
System.out.println(Arrays.toString(arr));
System.arraycopy(arr2, 0, arr, 0, 4);
System.out.println(Arrays.toString(arr));
[0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0] [11, 12, 23, 23, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
add(int index,E element)
public void add(int index, E element) {
//判断添加位置合法性
rangeCheckForAdd(index);
//上面分析过了
ensureCapacityInternal(size + 1); // Increments modCount!!
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
elementData[index] = element;
size++;
}
private void rangeCheckForAdd(int index) {
if (index > size || index < 0)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
addAll(Collection c)
public boolean addAll(Collection c) {
Object[] a = c.toArray();
int numNew = a.length;
ensureCapacityInternal(size + numNew); // Increments modCount
System.arraycopy(a, 0, elementData, size, numNew);
size += numNew;
return numNew != 0;
}
addAll(int index, Collection c)
public boolean addAll(int index, Collection c) {
rangeCheckForAdd(index);
Object[] a = c.toArray();
int numNew = a.length;
ensureCapacityInternal(size + numNew); // Increments modCount
int numMoved = size - index;
if (numMoved > 0)
System.arraycopy(elementData, index, elementData, index + numNew,
numMoved);
System.arraycopy(a, 0, elementData, index, numNew);
size += numNew;
return numNew != 0;
}
remove(int index)
public E remove(int index) {
rangeCheck(index);
modCount++;
E oldValue = elementData(index);
int numMoved = size - index - 1;
//表示移动元素的个数，也是元素移动的步数
if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
elementData[--size] = null; // clear to let GC do its work
return oldValue;
}
remove(Object o)
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 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
}