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Get Trained And Certified. What are the principle concepts of OOPS? They are: Abstraction Polymorphism Inheritance Encapsulation i. Related Article - Data Types in java 2. What is Abstraction? What is Encapsulation? What is the difference between Abstraction and Encapsulation? Top 10 Programming Languages that you need to watch out to boost your career in 5. What is Inheritance? The two most common reasons to use inheritance are: To promote code reuse To use polymorphism Core Java Interview Questions for Freshers 6.
What is Polymorphism? How does Java implement polymorphism? Explain the different forms of Polymorphism. Note : From a practical programming viewpoint, polymorphism manifests itself in three distinct forms in Java: Method overloading Method overriding through inheritance Method overriding through the Java interface 9.
What is runtime polymorphism or dynamic method dispatch? What is Dynamic Binding? What is method overloading? Overloaded methods CAN change the return type.
Overloaded methods CAN change the access modifier. Overloaded methods CAN declare new or broader checked exceptions. A method can be overloaded in the same class or in a subclass. What is method overriding? Related Article - Operators in Java What is the difference between method overloading and method overriding?
Happens at compile time. Must not throw new or broader checked exceptions Access — Must not make more restrictive can be less restrictive Invocation — Object type determines which method is selected. Can overloaded methods be overridden too? Explore Core Java Sample Resumes! Is it possible to override the main method?
A Class which doesn't provide complete implementation is defined as an abstract class. Abstract classes enforce abstraction. Can a abstract class be declared final? An abstract class without being inherited is of no use and hence will result in compile time error.
What is use of a abstract variable? Variables can't be declared as abstract. Can you create an object of an abstract class? Abstract classes can't be instantiated. Can a abstract class be defined without any abstract methods? Yes it's possible. This is basically to avoid instance creation of the class.
Class C implements Interface I containing method m1 and m2 declarations. Class C has provided implementation for method m2. Can i create an object of Class C? No not possible. Class C should provide implementation for all the methods in the Interface I. Since Class C didn't provide implementation for m1 method, it has to be declared as abstract. Can a method inside a Interface be declared as final? Doing so will result in compilation error. 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? A Class can extend only one class but can implement any number of Interfaces.
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? Doing so so will result in compilation error. Can a class be defined inside an Interface?
Can an Interface be defined inside a class? What is a Marker Interface? An Interface which doesn't have any declaration inside but still enforces a mechanism. Which object oriented Concept is achieved by using overloading and overriding? 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? What is Externalizable? Externalizable is an Interface that extends Serializable Interface.
And sends data into Streams in Compressed Format. 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. 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. 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? What restrictions are placed on method overloading?
Two methods may not have the same name and argument list but different return types. 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? 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.
What is Downcasting? Downcasting is the casting from a general to a more specific type, i. What modifiers may be used with an inner class that is a member of an outer class? A non-local inner class may be declared as public, protected, private, static, final, or abstract. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF uses bit and larger bit patterns. What restrictions are placed on the location of a package statement within a source code file? A package statement must appear as the first line in a source code file excluding blank lines and comments.
What is a native method? A native method is a method that is implemented in a language other than Java. What are order of precedence and associativity, and how are they used? Order of precedence determines the order in which operators are evaluated in expressions. Associatity determines whether an expression is evaluated left-to-right or right-to-left. Can an anonymous class be declared as implementing an interface and extending a class?
An anonymous class may implement an interface or extend a superclass, but may not be declared to do both. What is the range of the char type? The range of the char type is 0 to - 1 i. What is the range of the short type? The range of the short type is - to - 1. Why isn't there operator overloading? What does it mean that a method or field is "static"? Static variables and methods are instantiated only once per class. In other words they are class variables, not instance variables.
If you change the value of a static variable in a particular object, the value of that variable changes for all instances of that class. Static methods can be referenced with the name of the class rather than the name of a particular object of the class though that works too. That's how library methods like System. System class. Is null a keyword? Latest new arrivals tutorials on java interview questions and answers for freshers pdf free download for all users - 1.
The following list contains important Core Java interview questions for freshers as well as Java interview questions and answers for experienced programmers to help them prepare for the interview. This interview section questions contains a brief introduction to the Java. It is intended as a tutorial on the Java, and commonly asked qestions in all interviews.
As per my experience, good interviewers hardly planned to ask any particular question during your interview, normally questions start with some basic concept of. These questions make your mind linger and go through actual projects and scenarios.
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