Arraylist 与 Linklist
继承与实现
ArrayList:
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
Linklist:
public class LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable
Vector
public class Vector<E>
extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
数据结构
ArrayList:
线程不安全
对象数组:始长度为10
扩容函数:
elementData = Arrays.copyOf(elementData, newCapacity);
扩容方案:每次扩容是原先的1.5 倍
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
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);
}
Linklist:
双向链表:
线程不安全，多线程下容易出现这些异常:
java.util.ConcurrentModificationException
java.util.LinkedList$ListItr.checkForComodification(Unknown Source)
java.util.LinkedList$ListItr.next(Unknown Source)
Linklist记录了首尾两个节点，可以删除首部和尾部，也可以查询第一个数据和最后一个数据。
线程安全:
ArrayList LinkList Vector 线程安全测试
写一个for循环 循环 10000次，循环内开三个子线程，向list数组添加一条数据。
最后输出 List长度，
Vector 输出长度为 30000
ArrayList 输出长度小于 30000
Linklist 输出长度也小于 30000
结论:Vector 单次操作，例如 add remove size,trimeSize,get 都是加锁的，互斥执行
线程不安全代码:
int index = (int) Math.floor(Math.random()*list.size());
System.out.println("index="+index+" list.size()="+list.size());
if(list.size()>0) {
list.remove(index);
}
原因: 此线程list.size()是一个枷锁的操作，得到数组长度后，会释放 Vector的锁，这个时候其他线程可能会获取到Vector锁，可能进行删除操作。
然后再此获取到锁的时候，可能数组的长度就发生了变化，移除的时候出现数组越界问题。
这段代码: 问题是，两次获取Vector的锁，两次释放它，在这中间是不安全的。
。
Vector<String> list = new Vector<>();
for(int i=0;i<10000;i++)
{
Thread t1 = new Thread(){
@Override
public void run() {
list.add(Math.random()+"00");
}
};
Thread t2 = new Thread(){
@Override
public void run() {
int index = (int) Math.floor(Math.random()*list.size());
if(list.size()>0&&index<list.size()) {
System.out.println("index = " + index + " "+"list.size()="+list.size());
list.remove(index);
}
}
};
// Thread t3 = new Thread(){
// @Override
// public void run() {
// int index = (int) Math.floor(Math.random()*list.size());
// if(list.size()>0&&index<list.size()) {
// System.out.println("index = " + index + " "+"value="+list.get(index));
// }
// }
// };
t1.start();
t2.start();
// t3.start();
}
}
stack源码
package java.util;
/**
* The <code>Stack</code> class represents a last-in-first-out
* (LIFO) stack of objects. It extends class <tt>Vector</tt> with five
* operations that allow a vector to be treated as a stack. The usual
* <tt>push</tt> and <tt>pop</tt> operations are provided, as well as a
* method to <tt>peek</tt> at the top item on the stack, a method to test
* for whether the stack is <tt>empty</tt>, and a method to <tt>search</tt>
* the stack for an item and discover how far it is from the top.
* <p>
* When a stack is first created, it contains no items.
*
* <p>A more complete and consistent set of LIFO stack operations is
* provided by the {@link Deque} interface and its implementations, which
* should be used in preference to this class. For example:
* <pre> {@code
* Deque<Integer> stack = new ArrayDeque<Integer>();}</pre>
*
* @author Jonathan Payne
* @since JDK1.0
*/
public
class Stack<E> extends Vector<E> {
/**
* Creates an empty Stack.
*/
public Stack() {
}
/**
* Pushes an item onto the top of this stack. This has exactly
* the same effect as:
* <blockquote><pre>
* addElement(item)</pre></blockquote>
*
* @param item the item to be pushed onto this stack.
* @return the <code>item</code> argument.
* @see java.util.Vector#addElement
*/
public E push(E item) {
addElement(item);
return item;
}
/**
* Removes the object at the top of this stack and returns that
* object as the value of this function.
*
* @return The object at the top of this stack (the last item
* of the <tt>Vector</tt> object).
* @throws EmptyStackException if this stack is empty.
*/
public synchronized E pop() {
E obj;
int len = size();
obj = peek();
removeElementAt(len - 1);
return obj;
}
/**
* Looks at the object at the top of this stack without removing it
* from the stack.
*
* @return the object at the top of this stack (the last item
* of the <tt>Vector</tt> object).
* @throws EmptyStackException if this stack is empty.
*/
public synchronized E peek() {
int len = size();
if (len == 0)
throw new EmptyStackException();
return elementAt(len - 1);
}
/**
* Tests if this stack is empty.
*
* @return <code>true</code> if and only if this stack contains
* no items; <code>false</code> otherwise.
*/
public boolean empty() {
return size() == 0;
}
/**
* Returns the 1-based position where an object is on this stack.
* If the object <tt>o</tt> occurs as an item in this stack, this
* method returns the distance from the top of the stack of the
* occurrence nearest the top of the stack; the topmost item on the
* stack is considered to be at distance <tt>1</tt>. The <tt>equals</tt>
* method is used to compare <tt>o</tt> to the
* items in this stack.
*
* @param o the desired object.
* @return the 1-based position from the top of the stack where
* the object is located; the return value <code>-1</code>
* indicates that the object is not on the stack.
*/
public synchronized int search(Object o) {
int i = lastIndexOf(o);
if (i >= 0) {
return size() - i;
}
return -1;
}
/** use serialVersionUID from JDK 1.0.2 for interoperability */
private static final long serialVersionUID = 1224463164541339165L;
}
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