What is synchronization and why is it important?

With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object’s value. This often leads to significant errors.

What is an object’s lock and which object’s have locks

An object’s lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object’s lock.

All objects and classes have locks. A class’s lock is acquired on the class’s Class object.

What method must be implemented by all threads

All tasks must implement the run() method, whether they are a subclass of Thread or implement theRunnable interface.

What state is a thread in when it is executing?

An executing thread is in the running state.

What is the class and interface in java to create thread and which is the most advantageous method?

Thread class and Runnable interface can be used to create threads and using Runnable interface is the most advantageous method to create threads because we need not extend thread class here.

What is the use of the finally block? Is finally block in Java guaranteed to be called? When finally block is NOT called?

Finally is the block of code that executes always. The code in finally block will execute even if an exception is occurred. Finally block is NOT called in following conditions

If the JVM exits while the try or catch code is being executed, then the finally block may not execute. This may happen due to System.exit() call.
if the thread executing the try or catch code is interrupted or killed, the finally block may not execute even though the application as a whole continues.
If a exception is thrown in finally block and not handled then remaining code in finally block may not be executed.

What is immutable object in Java? Can you change values of a immutable object?

A Java object is considered immutable when its state cannot change after it is created. Use of immutable objects is widely accepted as a sound strategy for creating simple, reliable code. Immutable objects are particularly useful in concurrent applications. Since they cannot change state, they cannot be corrupted by thread interference or observed in an inconsistent state. java.lang.String and java.lang.Integer classes are the Examples of immutable objects from the Java Development Kit. Immutable objects simplify your program due to following characteristics :

Immutable objects are simple to use test and construct.
Immutable objects are automatically thread-safe.
Immutable objects do not require a copy constructor.
Immutable objects do not require an implementation of clone.
Immutable objects allow hashCode to use lazy initialization, and to cache its return value.
Immutable objects do not need to be copied defensively when used as a field.
Immutable objects are good Map keys and Set elements (Since state of these objects must not change while stored in a collection).
Immutable objects have their class invariant established once upon construction, and it never needs to be checked again.

Immutable objects always have “failure atomicity” (a term used by Joshua Bloch) if an immutable object throws an exception, it’s never left in an undesirable or indeterminate state

What are three ways in which a thread can enter the waiting state

A thread can enter the waiting state by invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object’s lock, or by invoking an object’s wait() method. It can also enter the waiting state by invoking its (deprecated) suspend() method.

How does multithreading take place on a computer with a single CPU

The operating system’s task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially.

What is the relationship between clipping and repainting

When a window is repainted by the AWT painting thread, it sets the clipping regions to the area of the window that requires repainting.