Java Interview Questions
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1. What is Java?

Java is a Programming language that offers software for many companies. When you write a Java application, that code will run on so many operating systems. Like MAC OS, Linux, Windows. Java gets syntax from C and C ++.

[ Related Article – What is Java? ]

2. What do you understand by Java?

  1. Java is an object-oriented computer language.
  2. It’s a high level programming language developed by James Gosling in Sun Microsystem in 1995.
  3. Java is a fast and secure reliable language used for many games, at the same devices and applications.

3. What do you mean by Object?

An object consists of methods and class which represent it’s formal and perform operations. A java program covers a lot of objects initiating each other their jobs. This concept is a like part of core java.

[ Related Article – Objects of implicits ]

4. What is class in Java?

Java compresses the codes in various classes which define new data categories. These new data categories are used to create objects.

[ Related Article – Event Classes in Servlet ]

5. Explain method overloading.

When a Java program encloses more than one method with the same name but changed properties, then it is called method overloading.

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6. Compare Overloading and Overriding.

Taxing refers to the case of having two methods of same name but changed properties, but overriding occurs when there are two methods of same name and properties, but one is in child class and one is in parental class.

7. Explain the creation of a thread-safe singleton in Java using double-checks locking

Singleton is designed with double check barring as before Java 5 acts as an adviser and it’s been possible to have multiple instances of Singleton when several threads creates an instance of Singleton at the same time. Java 5 made it easy to make thread-safe Singleton using Enum. Using a volatile variable is essential for the same.

9. Are constructors inherited? Can a subclass call the parent’s class constructor?

We cannot inherit a constructor. We create an instance of a subclass using a constructor of one of its super class. Since overrule the super class constructor is not our wish so that, we overcome a super class constructor, then we destroy the encapsulation abilities of the language.

10. Define JSON?

Development of JSON is “JavaScript Object Scheme”, It is a much lighter and readable substitute to XML. It’s an independent and easily parse-able in all programming languages. It is principally used for Collaborative between client – server or server -server communications. It is a much sunnier and clear alternative to XML.

11. Can we import same package/class two times? Will the JVM load the platform twice at runtime?

A platform or class can be inherited multiple times in a program code. JVM and compiler will not create any issue. Moreover JVM mechanically loads the class inside once regardless of times it is called in the program.

12. Java doesn’t use pointers. Why?

Cursors are susceptible and slight imprecision in their use may result in recollection problems and hence Java basically manages their use.

13. Distinguish between static loading and dynamic class loading?

Static loading – Paths are loaded statically with operative “new”.Dynamic class loading – It is a technique for programmatically invoking the functions of a class loader at run time. The syntax isClass.forName (Test className);

14. Explain Struts 1 Classes are not Thread Safe whereas Struts 2 classes are thread safe?

Struts 1 actions are a singleton. So all threads function on the single action object and later make it thread-unsafe.Struts 2 actions are not a singleton and a new action object copy are created each time a new action appeal is made and hence it strands safe.

15. Define an enumeration?

Usually, we called enumeration as an enum. An inventory is an interface containing methods for accessing the original data structure from which the listing is obtained. It allows sequential access to all the features stored in the collection.

16. How can we find the actual size of an object on the heap?

In Java, there is no way to find out the actual size of an object on the heap.

17. Which API is provided by Java for operations on a set of objects?

Java provides a Collection API which provides many useful methods which can be applied to a set of objects. Some of the main classes providing via Collection API include ArrayList, HashMap, TreeSet, and TreeMap.

18. What’s the base class of all exception classes?

Java.Lang.throwable – It is the super class of all exception classes and all exception classes are derived from this base class.

19. Why we used Vector class?

The Vector class provides the ability to execute a grow able array of objects. Vector proves to be very suitable if you don’t know the size of the array in advance, or we need one that can change sizes over the period of a program.

20. What is the default size of load factor in chopping based collection?

Default Size = 0.75. The default volume is computed as initial volume * load factor.

21. Explain Expression Language in JSP?

The mien semantic is used in JSP to simplify the accessibility of objects and it affords many objects that can be used straight like param, requestScope, sessionScope, applicationScope, request, session etc.

[ Related Article – Introduction to JSP ]

22. What are implicit objects?

Implicit objects, also called as pre-defined variables, are created by JSP Engine inside the service method so that it can be accessed directly without being declared explicitly.

[ Related Article – Objects of implicits ]

23. What is the front controller class of Spring MVC?

The Contributor Servlet class works as the front organizer in Spring MVC.

24. Write a syntax to convert a given Collection to Synchronized Collection?

Collections.synchronizedCollection(Collection collectionObj) will convert a given collection to synchronized collection.

25. What are latest features introduced with Java 8?

The below latest topographies are presented in Java 8. Lambda Languages, Interface Default and Static Devices, Method Reference, Parameters Name, Optional Streams, Concurrency.


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26. Mention the uses of Synchronized block

We are using Synchronized block because

It helps to deadlock an object for every shared supply.

The scope of synchronized block is smaller than the method.

27. Define Abstract class?

A class which comprises the abstract keyword in its assertion is known as abstract class. It can have immaterial and non-abstract systems (method with body).

This class can have open, isolated, protected or constants and default variables.

It needs to be protracted and its method employed. It cannot be instantiated.

If a class has at least one immaterial method, then the class must be stated abstract.

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