Dassault Systemes Most Frequently Asked Latest Core Java Interview Questions Answers
Can A Method Inside A Interface Be Declared As Final?
No not possible. Doing so will result in compilation error. public and abstract are the only applicable modifiers for method declaration in an interface.
Can An Interface Implement Another Interface?
Intefaces doesn't provide implementation hence a interface cannot implement another interface.
Can An Interface Extend Another Interface?
Yes an Interface can inherit another Interface, for that matter an Interface can extend more than one Interface.
Can A Class Extend More Than One Class?
Not possible. A Class can extend only one class but can implement any number of Interfaces.
Why Is An Interface Be Able To Extend More Than One Interface But A Class Can't Extend More Than One Class?
Basically Java doesn't allow multiple inheritance, so a Class is restricted to extend only one Class. But an Interface is a pure abstraction model and doesn't have inheritance hierarchy like classes(do remember that the base class of all classes is Object). So an Interface is allowed to extend more than one Interface.
Can An Interface Be Final?
Not possible. Doing it will result in compilation error.
Can A Class Be Defined Inside An Interface?
Yes it's possible.
Can An Interface Be Defined Inside A Class?
Yes it's possible.
What Is A Marker Interface?
An Interface which doesn't have any declaration inside but still enforces a mechanism.
Which Oo Concept Is Achieved By Using Overloading And Overriding?
Polymorphism.
If I Only Change The Return Type, Does The Method Become Overloaded?
No it doesn't. There should be a change in method arguements for a method to be overloaded.
Why Does Java Not Support Operator Overloading?
Operator overloading makes the code very difficult to read and maintain. To maintain code simplicity, Java doesn't support operator overloading.
Can We Define Private And Protected Modifiers For Variables In Interfaces?
No
What Is Externalizable?
Externalizable is an Interface that extends Serializable Interface. And sends data into Streams in Compressed Format. It has two methods, writeExternal(ObjectOuput out) and readExternal(ObjectInput in)
What Modifiers Are Allowed For Methods In An Interface?
Only public and abstract modifiers are allowed for methods in interfaces.
What Is A Local, Member And A Class Variable?
Variables declared within a method are "local" variables. Variables declared within the class i.e not within any methods are "member" variables (global variables). Variables declared within the class i.e not within any methods and are defined as "static" are class variables.
What Is An Abstract Method?
An abstract method is a method whose implementation is deferred to a subclass.
What Value Does Read() Return When It Has Reached The End Of A File?
The read() method returns -1 when it has reached the end of a file.
Can A Byte Object Be Cast To A Double Value?
No, an object cannot be cast to a primitive value.
What Is The Difference Between A Static And A Non-static Inner Class?
A non-static inner class may have object instances that are associated with instances of the class's outer class. A static inner class does not have any object instances.
What Is An Object's Lock And Which Object's Have Locks?
An object's lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object's lock. All objects and classes have locks. A class's lock is acquired on the class's Class object.
What Is The % Operator?
It is referred to as the modulo or remainder operator. It returns the remainder of dividing the first operand by the second operand.
When Can An Object Reference Be Cast To An Interface Reference?
An object reference be cast to an interface reference when the object implements the referenced interface.
Which Class Is Extended By All Other Classes?
The Object class is extended by all other classes.
Which Non-unicode Letter Characters May Be Used As The First Character Of An Identifier?
The non-Unicode letter characters $ and _ may appear as the first character of an identifier.
What Restrictions Are Placed On Method Overloading?
Two methods may not have the same name and argument list but different return types.
What Is Transient Variable?
Transient variable can't be serialize. For example if a variable is declared as transient in a Serializable class and the class is written to an ObjectStream, the value of the variable can't be written to the stream instead when the class is retrieved from the ObjectStream the value of the variable becomes null.
What Is Collection Api?
The Collection API is a set of classes and interfaces that support operation on collections of objects. These classes and interfaces are more flexible, more powerful, and more regular than the vectors, arrays, and hashtables if effectively replaces.
Example of classes: HashSet, HashMap, ArrayList, LinkedList, TreeSet and TreeMap.
Example of interfaces: Collection, Set, List and Map.
What Is Casting?
There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.
What Is The Return Type Of A Program's Main() Method?
void.
If A Variable Is Declared As Private, Where May The Variable Be Accessed?
A private variable may only be accessed within the class in which it is declared.
What Do You Understand By Private, Protected And Public?
These are accessibility modifiers. Private is the most restrictive, while public is the least restrictive. There is no real difference between protected and the default type (also known as package protected) within the context of the same package, however the protected keyword allows visibility to a derived class in a different package.
Can A Method Inside A Interface Be Declared As Final?
No not possible. Doing so will result in compilation error. public and abstract are the only applicable modifiers for method declaration in an interface.
Can An Interface Implement Another Interface?
Intefaces doesn't provide implementation hence a interface cannot implement another interface.
Can An Interface Extend Another Interface?
Yes an Interface can inherit another Interface, for that matter an Interface can extend more than one Interface.
Can A Class Extend More Than One Class?
Not possible. A Class can extend only one class but can implement any number of Interfaces.
Why Is An Interface Be Able To Extend More Than One Interface But A Class Can't Extend More Than One Class?
Basically Java doesn't allow multiple inheritance, so a Class is restricted to extend only one Class. But an Interface is a pure abstraction model and doesn't have inheritance hierarchy like classes(do remember that the base class of all classes is Object). So an Interface is allowed to extend more than one Interface.
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| Dassault Systemes Most Frequently Asked Latest Core Java Interview Questions Answers |
Can An Interface Be Final?
Not possible. Doing it will result in compilation error.
Can A Class Be Defined Inside An Interface?
Yes it's possible.
Can An Interface Be Defined Inside A Class?
Yes it's possible.
What Is A Marker Interface?
An Interface which doesn't have any declaration inside but still enforces a mechanism.
Which Oo Concept Is Achieved By Using Overloading And Overriding?
Polymorphism.
If I Only Change The Return Type, Does The Method Become Overloaded?
No it doesn't. There should be a change in method arguements for a method to be overloaded.
Why Does Java Not Support Operator Overloading?
Operator overloading makes the code very difficult to read and maintain. To maintain code simplicity, Java doesn't support operator overloading.
Can We Define Private And Protected Modifiers For Variables In Interfaces?
No
What Is Externalizable?
Externalizable is an Interface that extends Serializable Interface. And sends data into Streams in Compressed Format. It has two methods, writeExternal(ObjectOuput out) and readExternal(ObjectInput in)
What Modifiers Are Allowed For Methods In An Interface?
Only public and abstract modifiers are allowed for methods in interfaces.
What Is A Local, Member And A Class Variable?
Variables declared within a method are "local" variables. Variables declared within the class i.e not within any methods are "member" variables (global variables). Variables declared within the class i.e not within any methods and are defined as "static" are class variables.
What Is An Abstract Method?
An abstract method is a method whose implementation is deferred to a subclass.
What Value Does Read() Return When It Has Reached The End Of A File?
The read() method returns -1 when it has reached the end of a file.
Can A Byte Object Be Cast To A Double Value?
No, an object cannot be cast to a primitive value.
What Is The Difference Between A Static And A Non-static Inner Class?
A non-static inner class may have object instances that are associated with instances of the class's outer class. A static inner class does not have any object instances.
What Is An Object's Lock And Which Object's Have Locks?
An object's lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object's lock. All objects and classes have locks. A class's lock is acquired on the class's Class object.
What Is The % Operator?
It is referred to as the modulo or remainder operator. It returns the remainder of dividing the first operand by the second operand.
When Can An Object Reference Be Cast To An Interface Reference?
An object reference be cast to an interface reference when the object implements the referenced interface.
Which Class Is Extended By All Other Classes?
The Object class is extended by all other classes.
Which Non-unicode Letter Characters May Be Used As The First Character Of An Identifier?
The non-Unicode letter characters $ and _ may appear as the first character of an identifier.
What Restrictions Are Placed On Method Overloading?
Two methods may not have the same name and argument list but different return types.
What Is Transient Variable?
Transient variable can't be serialize. For example if a variable is declared as transient in a Serializable class and the class is written to an ObjectStream, the value of the variable can't be written to the stream instead when the class is retrieved from the ObjectStream the value of the variable becomes null.
What Is Collection Api?
The Collection API is a set of classes and interfaces that support operation on collections of objects. These classes and interfaces are more flexible, more powerful, and more regular than the vectors, arrays, and hashtables if effectively replaces.
Example of classes: HashSet, HashMap, ArrayList, LinkedList, TreeSet and TreeMap.
Example of interfaces: Collection, Set, List and Map.
What Is Casting?
There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.
What Is The Return Type Of A Program's Main() Method?
void.
If A Variable Is Declared As Private, Where May The Variable Be Accessed?
A private variable may only be accessed within the class in which it is declared.
What Do You Understand By Private, Protected And Public?
These are accessibility modifiers. Private is the most restrictive, while public is the least restrictive. There is no real difference between protected and the default type (also known as package protected) within the context of the same package, however the protected keyword allows visibility to a derived class in a different package.
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