More than 3000 questions in repository. There are more than 900 unanswered questions. Click here and help us by providing the answer. Have a video suggestion. Click Correct / Improve and please let us know.
Ans. Substitutability means that the type of the variable does not have to exactly match with the type of the value assigned to that variable. For example - Object reference of Parent object can hold derived object.
Help us improve. Please let us know the company, where you were asked this question :
Ans. Abstract methods are the methods that need to be overridden in the derived class ( either as implementing method or again abstract method ) so it's not only allowed but its required to override abstract method in the derived class.
Help us improve. Please let us know the company, where you were asked this question :
Ans. Yes, but in that case the derived class itself should be abstract. We cannot have an object of a class without definition for the method which has been declared abstract in the parent.
Help us improve. Please let us know the company, where you were asked this question :
Ans. Executor - Simple Interface that supports launching new tasks.
ExecutorService - Subinterface of Executor, which adds features that help manage the lifecycle, both of the individual tasks and of the Executor itself.
ScheduledExecutorService - Subinterface of ExecutorService, supports future and-or periodic execution of tasks.
Help us improve. Please let us know the company, where you were asked this question :
Ans. It doesn't matter how you define that method in implementing class. there will be only one definition provided and that method can be accessed using reference of either of the interfaces.
Help us improve. Please let us know the company, where you were asked this question :
Ans. Java provides a default constructor ( no argument ) if no constructor is provided by the programmer. Java makes a check during pre compilation if there is any constructor provided by the programmer. If any constructor is provided, Java understands that programmer has provided all the mechanism for initialization and construction of the object and may not even intend to create objects by calling a no argument constructor. For example - One may like to have objects created with self defined state otherwise restrict its creation.
We make the constructor private if we want to make a class singleton as we would like to restrict creation of new objects using new operator and default constructor. Similar could be the situation wherein we would like to construct objects in a particular manner only.
Help us improve. Please let us know the company, where you were asked this question :
Ans. Classes having only static methods in java is called util classes. As they don't have specific object state, they are basically intend to have shared code and state through static elements and methods. They save resources by sharing code.
Help us improve. Please let us know the company, where you were asked this question :
Ans. whenever a reference is created in Java without assigning the object
like
String str;
It get's assigned to null. So null provides a temporary memory location which any reference can point to till an appropriate object is assigned. Moreover it denotes that nothing has been assigned yet and hence provides a check in many cases.
Help us improve. Please let us know the company, where you were asked this question :
Ans. Null means nothing and hence means it's being assigned something till anything can be assigned to the reference. Null is a common memory location that get's assigned to any object reference till an actual object is assigned.
Empty object may not have a programmer initialized state but still a separate object in memory that has been assigned the placeholders.
Help us improve. Please let us know the company, where you were asked this question :
Ans. We can declare the reference as final to avoid reassignment but again we can always initialize the final reference to null. Even if there was any such facility available , it would have meant poor use of resources by assigning a new object in memory to each reference that's created. Many a times references are just meant to refer to other objects which already have a reference i.e sharing object by multiple references.
Help us improve. Please let us know the company, where you were asked this question :
Ans. A gobbler class take care of reading from a stream and optionally write out to another stream. Allows for non blocking reads when invoking a process through Runtime.exec(). Moreover the user can specify a callback that is called whenever anything is read from the stream.
Help us improve. Please let us know the company, where you were asked this question :
Ans. Garbage collection mechanism frees up the memory that is no longer needed. In languages like C / C++ the deallocation needs to be done explicitly by the programmer and hence any leniency may result in memory leak. Garbage collection in java ensures that all unused memory is reclaimed and hence there are no memory leaks.Moreover it relieves the programmer from the hassle of carefully releasing all memory.
Help us improve. Please let us know the company, where you were asked this question :
More than 3000 questions in repository.
Discuss 
core oops concepts 
Asked in 65 Companies 
basic 
frequent
Try 1 Question(s) Test
An Ideal Util class doesn't have ...
