这几天一直在搞关于优先级队列的实现,因为要考虑到线程的安全,所以PriorityQueue就不适用了。一个非常简单的实现方法,那就是把优先级比较好的插入一个队列,优先级低的插入另一个队列,取数的时候先在优先级高的队列上取数。这有个缺点就是如果优先级别越多的话,队列就越多。
因为要线程安全,队列采用 ConcurrentLinkedQueue 这个线程安全的,而api文档上说ConcurrentLinkedQueue 采用了有效的“无等待 (wait-free)”算法,所以它的吞吐量是很不错的!
简单代码如下:
package test;
import java.util.concurrent.ConcurrentLinkedQueue ;
public class PriorityQueueTest {
public static void main(String[] args) {
ConcurrentLinkedQueue <String> highPriority = new ConcurrentLinkedQueue <String>(); //高优先级
ConcurrentLinkedQueue <String> lowPriority = new ConcurrentLinkedQueue <String>(); //低优先级
highPriority.add( "aaa" );
highPriority.add( "bbb" );
highPriority.add( "111" );
lowPriority.add( "ccc" );
lowPriority.add( "ddd" );
lowPriority.add( "222" );
int i = 0 ,j = 0 , k= 0 ;
while ( true ){
while ( true ){
if (!highPriority.isEmpty()){
System.out.print(highPriority.remove());
i++;
k++;
System.out.println( ", i = " +i+ ", k=" +k);
break ;
}
if (!lowPriority.isEmpty()){
System.out.print(lowPriority.remove());
j++;
k++;
System.out.println( ", j = " +j+ ", k=" +k);
break ;
}
break ;
}
try {
Thread.sleep( 100 );
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
还有一种是,通过继承PriorityQueue 并实现Comparable接口,然后自已重写过compareTo方法就能实现很强大的优先级队列了,不过缺点是线程不安全的!
代码如下:
package test;
import java.util.PriorityQueue;
public class PriorityTest extends PriorityQueue<PriorityTest.Test>{
static class Test implements Comparable<Test>{
String packet;
int priotity;
public Test(String packet, int priotity) {
this .packet = packet;
this .priotity = priotity;
}
public int compareTo(Test arg) {
if (priotity < arg.priotity)
return 1 ;
else if (priotity > arg.priotity)
return - 1 ;
else
return 0 ;
}
public String toString(){
return packet;
}
}
public void add(String str, int priority){
super .add( new Test(str,priority));
}
public static void main(String args[]){
PriorityTest pTest = new PriorityTest();
pTest.add( "aaa" , 3 ); //优先级最高
pTest.add( "bbb" , 2 );
pTest.add( "ccc" , 1 );
while (!pTest.isEmpty()){
System.out.println(pTest.remove());
}
}