快速了解Java中ThreadLocal类

public class Test{
	//定义ThreadLocal 
	private static ThreadLocal name;
	public static void main(String[] args) throws Exception{
		name = new ThreadLocal();
		//Define Thread A
		Thread a = new Thread(){
			public void run(){
				System.out.println("Before invoke set,value is:"+name.get());
				name.set(“Thread A”);
				System.out.println("After invoke set, value is:"+name.get());
			}
		}
		;
		//Define Thread B
		Thread b = new Thread(){
			public void run(){
				System.out.println("Before invoke set,value is :"+name.get());
				name.set(“Thread B”);
				System.out.println("After invoke set,value is :"+name.get());
			}
		}
		;
		// Not invoke set, print the value is null
		System.out.println(name.get());
		// Invoke set to fill a value
		name.set(“Thread Main”);
		// Start thread A
		a.start();
		a.join();
		// Print the value after changed the value by thread A
		System.out.println(name.get());
		// Start thread B
		b.start();
		b.join();
		// Print the value after changed the value by thread B
		System.out.println(name.get())
	}
}

// Class that statistic the cost time
public class StatisticCostTime{
	// record the startTime
	// private ThreadLocal startTime = new ThreadLocal();
	private long startTime;
	// private ThreadLocal costTime = new ThreadLocal();
	private long costTime;
	private StatisticCostTime(){
	}
	//Singleton
	public static final StatisticCostTime shareInstance(){
		return InstanceFactory.instance;
	}
	private static class InstanceFactory{
		private static final StatisticCostTime instance = new StatisticCostTime();
	}
	// start
	public void start(){
		// startTime.set(System. nanoTime ());
		startTime = System.nanoTime();
	}
	// end
	public void end(){
		// costTime.set(System. nanoTime () - startTime.get());
		costTime = System.nanoTime() - startTime;
	}
	public long getStartTime(){
		return startTime;
		// return startTime.get();
	}
	public long getCostTime(){
		// return costTime.get();
		return costTime;
	}

public class Main{
	public static void main(String[] args) throws Exception{
		// Define the thread a
		Thread a = new Thread(){
			public void run(){
				try{
					// start record time
					StatisticCostTime.shareInstance().start();
					sleep(200);
					// print the start time of A 
					System.out.println("A-startTime:"+StatisticCostTime.shareInstance().getStartTime());
					// end the record
					StatisticCostTime.shareInstance().end();
					// print the costTime of A   
					System.out.println("A:"+StatisticCostTime.shareInstance().getCostTime());
				}
				catch(Exception e){
				}
			}
		}
		;
		// start a
		a.start();
		// Define thread b
		Thread b = new Thread(){
			public void run(){
				try{
					// record the start time of B1
					StatisticCostTime.shareInstance().start();
					sleep(100);
					// print the start time to console
					System.out.println("B1-startTime:"+StatisticCostTime.shareInstance().getStartTime());
					// end record start time of B1
					StatisticCostTime.shareInstance().end();
					// print the cost time of B1
					System.out.println("B1:"+StatisticCostTime.shareInstance().getCostTime());
					// start record time of B2
					StatisticCostTime.shareInstance().start();
					sleep(100);
					// print start time of B2
					System.out.println("B2-startTime:"+StatisticCostTime.shareInstance().getStartTime());
					// end record time of B2
					StatisticCostTime.shareInstance().end();
					// print cost time of B2
					System.out.println("B2:"+StatisticCostTime.shareInstance().getCostTime());
				}
				catch(Exception e){
				}
			}
		}
		;
		b.start();
	}
}

/**
 * Sets the value of this variable for the current thread. If set to
 * {@code null}, the value will be set to null and the underlying entry will
 * still be present.
 *
 * @param value the new value of the variable for the caller thread.
 */
public void set(T value) {
  Thread currentThread = Thread.currentThread();
  Values values = values(currentThread);
  if (values == null) {
    values = initializeValues(currentThread);
  }
  values.put(this, value);
}

/**
 * Returns the value of this variable for the current thread. If an entry
 * doesn't yet exist for this variable on this thread, this method will
 * create an entry, populating the value with the result of
 * {@link #initialValue()}.
 *
 * @return the current value of the variable for the calling thread.
 */
@SuppressWarnings("unchecked")
public T get() {
  // Optimized for the fast path.
  Thread currentThread = Thread.currentThread();
  Values values = values(currentThread);
  if (values != null) {
    Object[] table = values.table;
    int index = hash & values.mask;
    if (this.reference == table[index]) {
      return (T) table[index + 1];
    }
  } else {
    values = initializeValues(currentThread);
  }
  return (T) values.getAfterMiss(this);
}

/**
 * Creates Values instance for this thread and variable type.
 */
Values initializeValues(Thread current) {
  return current.localValues = new Values();
}

/**
 * Gets Values instance for this thread and variable type.
 */
Values values(Thread current) {
  return current.localValues;
}