AtomicInteger，一個提供原子操作的Integer的類。在Java語言中，++i和i++操作并不是線程安全的，在使用的時候，不可避免的會用到synchronized關鍵字。而AtomicInteger則通過一種線程安全的加減操作接口。
來看AtomicInteger提供的接口。
//獲取當前的值
public final int get()
//取當前的值，并設置新的值
?public final int getAndSet(int newValue)
//獲取當前的值，并自增
?public final int getAndIncrement()
//獲取當前的值，并自減
public final int getAndDecrement()
//獲取當前的值，并加上預期的值
public final int getAndAdd(int delta)
... ...
下面是一個對比測試，我們寫一個synchronized的方法和一個AtomicInteger的方法來進行測試，直觀的感受下性能上的差異
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package
?zl.study.concurrency;??
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import
?java.util.concurrent.atomic.AtomicInteger;??
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public
?
class
?AtomicIntegerCompareTest?{??
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????private?int?value;??
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??????
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????public?AtomicIntegerCompareTest(int?value){??
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????????this.value?=?value;??
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????}??
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??????
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????public?synchronized?int?increase(){??
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????????return?value++;??
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????}??
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??????
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????public?static?void?main(String?args[]){??
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????????long?start?=?System.currentTimeMillis();??
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??????????
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????????AtomicIntegerCompareTest?test?=?new?AtomicIntegerCompareTest(0);??
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????????for(?int?i=0;i<?1000000;i++){??
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????????????test.increase();??
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????????}??
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????????long?end?=?System.currentTimeMillis();??
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????????System.out.println("time?elapse:"+(end?-start));??
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??????????
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????????long?start1?=?System.currentTimeMillis();??
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??????????
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????????AtomicInteger?atomic?=?new?AtomicInteger(0);??
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??????????
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????????for(?int?i=0;i<?1000000;i++){??
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????????????atomic.incrementAndGet();??
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????????}??
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????????long?end1?=?System.currentTimeMillis();??
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????????System.out.println("time?elapse:"+(end1?-start1)?);??
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??????????
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??????????
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????}??
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}??
結果
time elapse:31
time elapse:16
由此不難看出，通過JNI本地的CAS性能遠超synchronized關鍵字
?
Reference
http://stackoverflow.com/questions/2443239/java-atomicinteger-what-are-the-differences-between-compareandset-and-weakcompar