标签：有关 lin order limit 指定 拷贝 == 没有 cep
??此处的集合指的是java集合框架中的实现了Collection接口相关的类。所以主要为List Set 和 Queue 其他章节会专门介绍Map相关。
/**
* Constructs an empty list with an initial capacity of ten.
*/
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}/**
* Constructs an empty list with the specified initial capacity.
*
* @param initialCapacity the initial capacity of the list
* @throws IllegalArgumentException if the specified initial capacity
* is negative
*/
public ArrayList(int initialCapacity) {
if (initialCapacity > 0) {
// 直接指定 没有扩容操作
this.elementData = new Object[initialCapacity];
} else if (initialCapacity == 0) {
this.elementData = EMPTY_ELEMENTDATA;
} else {
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
}
}/**
* Constructs a list containing the elements of the specified
* collection, in the order they are returned by the collection's
* iterator.
*
* @param c the collection whose elements are to be placed into this list
* @throws NullPointerException if the specified collection is null
*/
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;
}
} private static final long serialVersionUID = 8683452581122892189L;
/**
* Default initial capacity.
*/
// 默认容量
private static final int DEFAULT_CAPACITY = 10;
/**
* Shared empty array instance used for empty instances.
*/
private static final Object[] EMPTY_ELEMENTDATA = {};
/**
* Shared empty array instance used for default sized empty instances. We
* distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
* first element is added.
*/
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
/**
* The array buffer into which the elements of the ArrayList are stored.
* The capacity of the ArrayList is the length of this array buffer. Any
* empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
* will be expanded to DEFAULT_CAPACITY when the first element is added.
*/
transient Object[] elementData; // non-private to simplify nested class access
/**
* The size of the ArrayList (the number of elements it contains).
*
* @serial
*/
private int size;
// 数组最大的长度 其中通过最终的hugeCapacity()可以突破这个限制达到Integer.MAX_VALUE
// 数组需要-8: 有些虚拟机在数组中保留了一些头信息。避免内存溢出
/**
* The maximum size of array to allocate.
* Some VMs reserve some header words in an array.
* Attempts to allocate larger arrays may result in
* OutOfMemoryError: Requested array size exceeds VM limit
*/
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
需要注意的是ArrayList存储的最大量其实跟你设置的内存也是有关系的。
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)
// 将index后面的舒服复制到index处
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
//置空
elementData[--size] = null; // clear to let GC do its work
} // 添加函数
public boolean add(E e) {
ensureCapacityInternal(size + 1); // Increments modCount!!
elementData[size++] = e;
return true;
}
private void ensureCapacityInternal(int minCapacity) {
ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
}
private static int calculateCapacity(Object[] elementData, int minCapacity) {
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
return Math.max(DEFAULT_CAPACITY, minCapacity);//空数组扩容默认值和需要的长度 取最大值
}
return minCapacity;
}
private void ensureExplicitCapacity(int minCapacity) {
// modCount: 继承自AbstractList 用于防止一个迭代器(Iterator)对集合进行修改而另一个迭代器对其进行遍历时，产生混乱的现象(并发场景下)。与modCount 搭配的是 expectedModCount
modCount++;
// overflow-conscious code
// 需要的长度比数组长度大，此时确实需要扩容
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
// 目标扩容为原数组长度的1.5倍
int newCapacity = oldCapacity + (oldCapacity >> 1);
// 需要的长度比计算值大的话 取最大值
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
// 如果计算后的值比ArrayList 的MAX_ARRAY_SIZE属性还要大的话，进行终极扩容
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
// minCapacity is usually close to size, so this is a win:
// 拷贝到新数组中
elementData = Arrays.copyOf(elementData, newCapacity);
}
private static int hugeCapacity(int minCapacity) {
// 溢出
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
// 最大值为Integer.MAX_VALUE 此时多余的会被舍弃掉
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}散列集
队列的实现方式有两种： 数组或链表
有边界 但是效率高
优先级队列
标签：有关 lin order limit 指定 拷贝 == 没有 cep
原文地址：https://www.cnblogs.com/wei57960/p/12194508.html
