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Ans. Abstract classes provide a mechanism of interfacing ( using abstract method ) as well as code reuse through inheritance ( extending abstract class )
Comparing to concrete class they have an advantage of providing interface which a concrete class doesn't provide.
Comparing to interfaces they have an advantage of providing code reuse through inheritance which interfaces dont provide.
Ans. Keyword is a reserved word that has a pre defined meaning for the compiler and hence cannot be used as an identifier, for example - final, private , for etc.
Identifier is the name given by the programmer to a programming construct, for example - class and method names etc.
java Keywords cannot be used as an identifier in java.
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Ans. Keywords are the reserved words that have a pre defined meaning for a compiler whereas modifiers are the type of keywords that modifies the state or definition of a programming construct.
for, while are keywords but not modifiers.
private , public , final , abstract etc are keywords as well as modifiers.
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Ans. Access modifiers are the java reserved keywords that changes the access privileges on a class , method , element etc. For example - public , private and protected.
Non Access modifiers are the java modifiers other than access modifiers. For example - static , final, abstract, synchronized, transient, volatile etc.
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Ans. synchronized is a keyword and a modifier. The synchronized keyword is used to indicate that a method can be accessed exclusively by one thread at a time.
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Ans. it depends on the implementation of equals method of the respective class. If no definition is provided and it uses the default definition of the object class, two references are equal only if they point to the same object.
We can have such an equality defined for a particular class objects if we provide appropriate implementation of equals method comparing all those fields.
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Ans. Frankly saying I dont see much use of method overloading as its just little design convenience as you can use the same name but still have binding to different methods depending on the need.
Method overriding is really important and is much more useful than method overloading. Along with other programming concepts like interfaces and dependency injection , it facilitates the development of software as libraries and plug-gable components.
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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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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. 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. 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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Q625. 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. 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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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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