Java Learning (11): Java lock synchronized, object lock and Class lock example

Java locks are divided into object locks and class locks.

1. When two concurrent threads access the same object in the synchronized (this) synchronization code block, only one thread can be executed for that object within a single time. The other thread must wait for the current thread to finish executing the block before it can execute the code block.

2. However, another thread can still access the non-synchronized (this) synchronous code block in the object.

　　3. In particular, when a thread accesses a synchronized (this) synchronization block of object, the access of other threads to all other synchronized (this) synchronization blocks in the object is blocked.

4. Synchronous locking is the object, not the code. Therefore, if you have a synchronization method in your class, this method can be executed by two different threads at the same time, as long as each thread creates an instance of the class itself.

5. The Synchronized method of different object instances is non-interfering. In other words, other threads can access the Synchronized method in another object instance of the same class at the same time.

6 The . Synchronized keyword cannot be inherited, that is, the method of the base class synchronized F () {} is not automatically synchronized F () {} in the inheriting class, but instead becomes F () {}. Inheriting a class requires that you explicitly specify one of its methods as the Synchronized method.

7. When a global object or class is locked, all objects of that class function.

Class Lock Example

To lock a global variable:

1  Public classMysynchronizedextendsThread2 {3     Private intVal;4     5     Private StaticObject lock =NewObject ();6     7      PublicMysynchronized (intv)8     {9val =v;Ten     } One      A      Public voidPrintval (intv) -     { -         synchronized(Lock) the         { -              while(true) -             { - System.out.println (v); +             } -         } +     } A      at      Public voidRun () -     { - Printval (val); -     } -}

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Lock the entire class:

1  Public classMysynchronizedextendsThread2 {3     Private intVal;4     5      PublicMysynchronized (intv)6     {7val =v;8     }9     Ten      Public voidPrintval (intv) One     { A         synchronized(mysynchronized.class) -         { -              while(true) the             { - System.out.println (v); -             } -         } +     } -      +      Public voidRun () A     { at Printval (val); -     } -}

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Additional Lock Examples:

1  Public classMysynchronizedextendsThread2 {3     PrivateString name;4     5     PrivateString Val;6     7      Publicmysynchronized (string name, String v)8     {9          This. Name =name;Tenval =v; One     } A      -      Public voidPrintval () -     { the         synchronized(val) -         { -              while(true) -             { +SYSTEM.OUT.PRINTLN (name +val); -             } +         } A     } at      -      Public voidRun () -     { - printval (); -     } -      in      Public Static voidMain (String args[]) -     { toMysynchronized F1 =NewMysynchronized ("Foo 1:", "Printval"); + F1.start (); -mysynchronized F2 =NewMysynchronized ("Foo 2:", "Printval"); the F2.start (); *     } $}

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The particularity of a string constant, belonging to the same object.

Java Learning (11): Java lock synchronized, object lock and Class lock example