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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.
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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.
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Ans. Include directive includes the file at translation time (the phase of JSP life cycle where the JSP gets converted into the equivalent servlet) whereas the include action includes the file at runtime.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Ans. The objective of an abstract class is to provide an interface as well as code reuse. Though we cannot instantiate an instance of abstract class but we can reuse the code by extending such a class. Moreover abstract class provides interfacing to outside components just like interfaces.
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Q1053. If we don't provide any argument to the executed program, What arguments will be passed to the main method ? Will the String array argument be null ?
Ans. Constructors are used to initialize the state of an object. If there are no constructor , objects won't have any initialized state and hence it's elements may contain garbage values. If the memory were used as is, the behavior of the object would also be unpredictable.
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Ans. JVM (Java Virtual Machine) is an abstract machine. It is a specification that provides runtime environment in which java bytecode can be executed.JVMs are available for many hardware and software platforms (i.e. JVM is platform dependent).Runtime Instance Whenever you write java command on the command prompt to run the java class, an instance of JVM is createdThe JVM performs following operation:Loads codeVerifies codeExecutes codeProvides runtime environment
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Ans. Counter controlled repetitions are the loops that are controlled with the use of counters or the loops where the number of repetitions are known in advance. for loop in java is the counter controlled repetition.
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Ans. It's a programming technique wherein the method can call itself. The method call usually involves a different set of parameters as otherwise it would lead to an infinite loop. There is usually a termination check and statement to finally return the control out of all function calls.
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