Using explicit lock gives you more control but you have to put more effort. Remember that using synchronized keyword is easier and less error-prone then using explicit lock. Do the methods contain internal locks that control the locking and unlocking of the data for multiple thread access No, despite the keyword being on the method, it is the object which is locked, not the method. This means the thread can wake up itself after a specified timeout expires. What does it mean that Vectors contain synchronized methods The methods have been marked as synchronized. Specify a timeout while a thread is waiting.Use more than one Condition objects associate with a Lock.You can still choose to synchronize any collection you need to using methods in, but its your choice. We learned that synchronization as a default meant poor performance, so it was reversed when the Java Collections API came out. Consider using explicit Lock and Condition objects if you want to have greater control over the synchronization process: Vector was part of JDK 1.0 ArrayList was not.Consider using the synchronized keyword if you want to block concurrent access to instance methods (non-static synchronized methods) or static methods (static synchronized methods).If you refer to second paragraph on documentation, it clearly quoted that operations behave as if they occur in serial order. A static synchronized method is locked on the Class object. Additionally, only one thread at a time can execute any method/block locked on the same object. Now the question is: when to use which? When to use Lock and when to use synchronized?Here are some guidelines that help you make your decision: the answer is: getChars () will wait till other synchronized methods complete the execution and release lock. Any 'synchronized' method or block is 'locked' on entry such that only one thread at a time can execute that method/block (relative to the lock object). Intrinsic locking using the synchronized keyword.Explicit locking using Lock and Condition objects.When one thread is executing a synchronized method for an object, all other threads that invoke synchronized methods for the same object block (suspend execution) until the first thread is done with the object. Intrinsic LockingSo far I have explained to you the work of two synchronization mechanism in Java: Straight from the Java documentation: It is not possible for two invocations of synchronized methods on the same object to interleave. They can run at the same time.That’s how the intrinsic (implicit) locking mechanism works in Java. It’s because synchronized static methods and synchronized non-static methods work on different locks: class lock and instance lock.In other words, a synchronized static method and a non-static synchronized method will not block each other. The synchronized non-static methods are still executable by other threads. Synchronized MethodsConsider the following class: public class A So when a thread is executing a synchronized static method, it also blocks access to all other synchronized static methods. This default lock is called intrinsic lock which belongs to every Java object.The synchronized keyword can be used at method level or code block level. Methods such as add (), get (), size (), etc, are all synchronized such that modifications to the internal structure of the Vector and access to that internal structure cannot be processed simultaneously by separate threads. And to make it easier for programmers, Java provides the synchronized keyword that operates on the default lock of a class. Vector is considered thread-safe because access the the internals of the Vector is synchronized. This is basically how synchronized is designed and working in Java. Both ArrayList and Vector are implemented internally as arrays, both are dynamically resized but Vector is has a capacityIncrement of double the current array size where for ArrayList it is half the current size. Synchronization has two forms: synchronized methods and synchronized statements.Welcome to part 3 of Java Synchronization Tutorial series! In part 2, you know how to use Lock and Condition objects for synchronizing access to a method. Making Vector synchronised is just the way the people who write that Java library decided to implement it. If you have two different instances, two different threads can use them at the same time, and they won’t block each other: MutableInteger integer1 = new MutableInteger ( ) MutableInteger integer2 = new MutableInteger ( ) // Threads are using different objects and don't // interact with each other Thread thread1 = new Thread ( new IncrementingRunnable (integer1 ) ) Thread thread2 = new Thread ( new IncrementingRunnable (integer2 ) ) How synchronized Works The synchronized keyword only limits thread access to one object. Synchronization in Java is a Java feature that restricts multiple threads from trying to access the commonly shared resources at the same time.
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