Java Interview Questions – Part3

Q: Define Inheritance?

A: It is the process where one object acquires the properties of another. With the use of inheritance the information is made manageable in a hierarchical order.

Q: When super keyword is used?

A: If the method overrides one of its superclass’s methods, overridden method can be invoked through the use of the keyword super. It can be also used to refer to a hidden field

Q: What is Polymorphism?

A: Polymorphism is the ability of an object to take on many forms. The most common use of polymorphism in OOP occurs when a parent class reference is used to refer to a child class object.

Q: What is Abstraction?

A: It refers to the ability to make a class abstract in OOP. It helps to reduce the complexity and also improves the maintainability of the system.

Q: What is Abstract class

A: These classes cannot be instantiated and are either partially implemented or not at all implemented. This class contains one or more abstract methods which are simply method declarations without a body.

Q: When Abstract methods are used?

A: If you want a class to contain a particular method but you want the actual implementation of that method to be determined by child classes, you can declare the method in the parent class as abstract.

Q: What is Encapsulation?

A: It is the technique of making the fields in a class private and providing access to the fields via public methods. If a field is declared private, it cannot be accessed by anyone outside the class, thereby hiding the fields within the class. Therefore encapsulation is also referred to as data hiding.

Q: What is the primary benefit of Encapsulation?

A: The main benefit of encapsulation is the ability to modify our implemented code without breaking the code of others who use our code. With this Encapsulation gives maintainability, flexibility and extensibility to our code.

Q: What is an Interface?

A: An interface is a collection of abstract methods. A class implements an interface, thereby inheriting the abstract methods of the interface.

Q: Give some features of Interface?

A: It includes:

• Interface cannot be instantiated
• An interface does not contain any constructors.
• All of the methods in an interface are abstract.

Q: Define Packages in Java?

A: A Package can be defined as a grouping of related types(classes, interfaces, enumerations and annotations ) providing access protection and name space management.

Q: Why Packages are used?

A: Packages are used in Java in-order to prevent naming conflicts, to control access, to make searching/locating and usage of classes, interfaces, enumerations and annotations, etc., easier.

Q: What do you mean by Multithreaded program?

A: A multithreaded program contains two or more parts that can run concurrently. Each part of such a program is called a thread, and each thread defines a separate path of execution.

Q: What are the two ways in which Thread can be created?

A: Thread can be created by: implementing Runnable interface, extending the Thread class.

Q: What is an applet?

A: An applet is a Java program that runs in a Web browser. An applet can be a fully functional Java application because it has the entire Java API at its disposal.

Q: An applet extend which class?

A: An applet extends java.applet.Applet class.

Q: Explain garbage collection in Java?

A: It uses garbage collection to free the memory. By cleaning those objects that is no longer reference by any of the program.

Q: Define immutable object?

A: An immutable object can’t be changed once it is created.

Q: Explain the usage of this() with constructors?

A: It is used with variables or methods and used to call constructer of same class.

Q: Explain Set Interface?

A: It is a collection of element which cannot contain duplicate elements. The Set interface contains only methods inherited from Collection and adds the restriction that duplicate elements are prohibited.

Q: Explain TreeSet?

A: It is a Set implemented when we want elements in a sorted order.

Q: What is Comparable Interface?

A: It is used to sort collections and arrays of objects using the collections.sort() and java.utils. The objects of the class implementing the Comparable interface can be ordered.

Q: Difference between throw and throws?

A: It includes:

• Throw is used to trigger an exception where as throws is used in declaration of exception.
• Without throws, Checked exception cannot be handled where as checked exception can be propagated with throws.

Q: Explain the following line used under Java Program:public static void main (String args[ ])

A: The following shows the explanation individually:

• public: it is the access specifier.
• static: it allows main() to be called without instantiating a particular instance of a class.
• void: it affirns the compiler that no value is returned by main().
• main(): this method is called at the beginning of a Java program.
• String args[ ]: args parameter is an instance array of class String

Q: Define JRE i.e. Java Runtime Environment?

A: Java Runtime Environment is an implementation of the Java Virtual Machine which executes Java programs. It provides the minimum requirements for executing a Java application;

Q: What is JAR file?

A: JAR files is Java Archive fles and it aggregates many files into one. It holds Java classes in a library. JAR files are built on ZIP file format and have .jar file extension.

Q: What is a WAR file?

A: This is Web Archive File and used to store XML, java classes, and JavaServer pages. which is used to distribute a collection of JavaServer Pages, Java Servlets, Java classes, XML files, static Web pages etc.