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Core Java - Interview Questions and Answers for 'Keywords' - 45 question(s) found - Order By Newest

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 Q1. Which of the following combination of keywords is illegal in Java ?

a. static and transient
b. transient and final
c. static and synchronized
d. abstract and final
Core Java
Ans. abstract and final

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Advanced level question usually asked to senior developers , leads and architects.
 Q2. How does volatile affect code optimization by compiler?Core Java
Ans. Volatile is an instruction that the variables can be accessed by multiple threads and hence shouldn't be cached. As volatile variables are never cached and hence their retrieval cannot be optimized.

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Frequently asked question for intermediate developers. Frequently asked in HCL Technologies and EPAM.
  Q3. What is Volatile keyword used for ?Core Java
Ans. Volatile is a declaration that a variable can be accessed by multiple threads and hence shouldnt be cached.

  Sample Code for volatile

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 Q4. Can we access instance variables within static methods ?Core Java
Ans. Yes.we cannot access them directly but we can access them using object reference.Static methods belong to a class and not objects whereas non static members are tied to an instance. Accessing instance variables without the instance handler would mean an ambiguity regarding which instance the method is referring to and hence its prohibited.

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  Q5. What is the use of Transient Keyword ?Core Java
Ans. It in Java is used to indicate that a field should not be serialized.

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 Q6. When we say final x = 10, is the reference final or the value ?Core Java
Ans. final keyword have meaning only to referenced and not the value. It means that the specified reference cannot be dereferenced. It doesn't control the value assigned to the memory that's being referenced. This is the reason that final object references doesn't mean that the object is immutable but means that the reference cannot be changed to point to new object.

In case of primitive types too, when we assign a reference to another, values are passed and not the object reference, and hence a new placeholder is created in memory with the same value. That is why final to that context means that you cannot change the assigned memory and there is no way we can have that memory place have another value.

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 Q7. What is a Final Method ?Core Java
Ans. A Method that cannot be overriden in the sub class.

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Very Frequently asked.Favorite question in Walk in drive for many Indian service companies.
 Q8. What is a Final Class ?
Ans. A Class that cannot be sub classed.

  Sample Code for final class

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 Q9. Can we override static methods ? Why ?Core Java
Ans. No.

Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.

A static method is not associated with any instance of a class so the concept of overriding for runtime polymorphism using static methods is not applicable.

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 Q10. What is "super" used for ?
Ans. Used to access members of the base class.

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 Q11. What is "this" keyword used for ?
Ans. Used to represent an instance of the class in which it appears.

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 Q12. What is "Import" used for ?Core Java
Ans. Enables the programmer to abbreviate the names of classes defined in a package.

  Sample Code for import

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 Q13. What is a Static import ?Core Java
Ans. By static import , we can access the static members of a class directly without prefixing it with the class name.

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 Q14. Why can't we use this in static context ?Core Java
Ans. Static methods can be called using instance references wherein this would have made sense but static method can also be called using Class name wherein this would mean nothing and hence forbidden.

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 Q15. Which of the following keyword is not permitted for outer class ?

a. public
b. abstract
c. final
d. protected
Ans. protected

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 Q16. What is the use of static keyword in Java ?Core Java
Ans. static keyword is used to specify that the respective programming construct ( method , variable ) belongs to the class and not to its instance and is supposed to be shared by all instances of the class.

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 Q17. What is the difference between a keyword and a modifier ?Core Java
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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 Q18. What is the difference between keywords, identifiers and literals in java ?Core Java
Ans. Keywords are the reserved words that have a pre defined meaning for the compiler and hence are restricted to be used as identifiers.

Identifiers are the name assigned to different programming constructs like classes, interfaces, methods , variables etc.

Literals are the values that are assigned to Identifiers.

For example

int count = 0;

in the above statement "int" is a keyword, "count" is an identifier and "0" is a literal

  Sample Code for keywords

  Sample Code for identifiers

  Sample Code for literals

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 Q19. Explain the use of "Native" keyword ?Core Java
Ans. Used in method declarations to specify that the method is not implemented in the same Java source file, but rather in another language

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 Q20. Can we use "this" within static method ? Why ?Core Java
Ans. No. Even though "this" would mean a reference to current object id the method gets called using object reference but "this" would mean an ambiguity if the same static method gets called using Class name.

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Rarely asked as default methods have been introduced with Java 8.
 Q21. Can we have a default method definition in the interface without specifying the keyword "default" ? Core Java
Ans. No. Compiler complains that its an abstract method and hence shouldn't have the body.

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 Q22. In majority of the situations it won't make much sense whether you append this with the instance method call.Can you tell a situation wherein this keyword would make sense in a instance method ? Core Java
Ans. Within instance method of the parent class that has other multiple methods that have been overridden by the derived classes.

In such case a simple method call from the common method will always be made to the method definition in the parent class. But If we use this.methodCall , this will be polymorphic and will be made to the respective derived object overriding method.

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 Q23. Which of the following is not the use of this keyword ?

a. Passing itself to another method
b. To call the static method
c. Referring to the instance variable when local variable has the same name
d. Calling another constructor in constructor chaining
Ans. To call the static method

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 Q24. Which of the following is not true for final variables ?

a. They cannot be changed after initialization
b. They can be initialized within static method
c. They can be declared and initialized together at the same place
d. They can be initialized within constructor
Ans. They can be initialized within static method

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 Q25. Which of the following is false for final ?

a. Final methods cannot be overriden
b. Final methods cannot be overloaded
c. Final classes cannot be subclassed
d. Final class cannot be abstract
Ans. Final methods cannot be overloaded

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 Q26. Can we add more elements to an array list that has been marked as final ?
Ans. Yes, the array list can hold more elements. Final only puts the restriction that the array list reference cannot hold any other array list.

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 Q27. Why can't we declare a class abstract as well as final ?Core Java
Ans. Abstract means that the class is only meant to be subclassed whereas final means that it cannot be subclassed so both concepts - abstract and final are actually mutually exclusive and hence not permitted together.

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 Q28. Does compiler treats it differently if we don't prefix this to the member element and its implicit as its the only variable available with that name ?
Ans. It makes no difference whether we add this to the variable or not. The only use of this is in the cases where there are multiple variables with the same name and we want to distinguish between the member variable and local variable. In case this is not added ,this is automatically added by the compiler in the byte code.

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 Q29. Is New Keyword a method Name ?Core Java
Ans. No, Its an Operator.

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 Q30. Name some of the Java Keywords ?Core Java
Ans. Static , Final , Synchronized, private , public , protected, volatile, transient, super, this,import , abstract,native,default (effective java 8), new

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