Java 中ThreadLocal類詳解。本站提示廣大學習愛好者：（Java 中ThreadLocal類詳解）文章只能為提供參考，不一定能成為您想要的結果。以下是Java 中ThreadLocal類詳解正文
ThreadLocal類，代表一個線程部分變量，經由過程把數據放在ThreadLocal中，可讓每一個線程創立一個該變量的正本。也能夠算作是線程同步的另外一種方法吧，經由過程為每一個線程創立一個變量的線程當地正本，從而防止並發線程同時讀寫統一個變量資本時的抵觸。
示例以下：
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import com.sun.javafx.webkit.Accessor;
public class ThreadLocalTest {
static class ThreadLocalVariableHolder {
private static ThreadLocal<Integer> value = new ThreadLocal<Integer>() {
private Random random = new Random();
protected synchronized Integer initialValue() {
return random.nextInt(10000);
}
};
public static void increment() {
value.set(value.get() + 1);
}
public static int get() {
return value.get();
}
}
static class Accessor implements Runnable{
private final int id;
public Accessor(int id) {
this.id = id;
}
@Override
public void run() {
while (!Thread.currentThread().isInterrupted()) {
ThreadLocalVariableHolder.increment();
System.out.println(this);
Thread.yield();
}
}
@Override
public String toString() {
return "#" + id + ": " + ThreadLocalVariableHolder.get();
}
}
public static void main(String[] args) {
ExecutorService executorService = Executors.newCachedThreadPool();
for (int i = 0; i < 5; i++) {
executorService.execute(new Accessor(i));
}
try {
TimeUnit.MICROSECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
executorService.shutdownNow();
}
}
運轉成果：
#1: 9685 #1: 9686 #2: 138 #2: 139 #2: 140 #2: 141 #0: 5255 。。。
由運轉成果可知，各線程都用於各自的Local變量，並各自讀寫互不攪擾。
ThreadLocal共供給了三個辦法來操作，set,get和remove。
在Android 中的Looper，即便用了ThreadLocal來為每一個線程都創立各自自力的Looper對象。
public final class Looper {
private static final String TAG = "Looper";
// sThreadLocal.get() will return null unless you've called prepare().
static final ThreadLocal<Looper> sThreadLocal = new ThreadLocal<Looper>();
private static void prepare(boolean quitAllowed) {
if (sThreadLocal.get() != null) {
throw new RuntimeException("Only one Looper may be created per thread");
}
sThreadLocal.set(new Looper(quitAllowed));
}
。。。
}
當某個線程須要本身的Looper及新聞隊列時，就挪用Looper.prepare()，它會為線程創立屬於線程的Looper對象及MessageQueue，並將Looper對象保留在ThreadLocal中。
