Java Interview Questions
1.How are Observer and Observable used?
Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.
2.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.
3.How does Java handle integer overflows and underflows?
It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.
4.Does garbage collection guarantee that a program will not run out of memory?
Garbage collection does not guarantee that a program will not run out of
memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection
5.What is the difference between preemptive scheduling and time slicing?
Under preemptive scheduling, the highest priority task executes until it enters
the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.
6.When a thread is created and started, what is its initial state?
A thread is in the ready state after it has been created and started.
7.What is the purpose of finalization?
The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.
8.What is the Locale class?
The Locale class is used to tailor program output to the conventions of a
particular geographic, political, or cultural region.
9.What is the difference between a while statement and a do statement?
A while statement checks at the beginning of a loop to see whether the next
loop iteration should occur. A do statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do statement will
always execute the body of a loop at least once.
10.What is the difference between static and non-static variables?
A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance.
11.How are this() and super() used with constructors?
this() is used to invoke a constructor of the same class. super() is used to
invoke a superclass constructor.
12.What are synchronized methods and synchronized statements?
Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.
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