Top Java Programming Interview Questions and Answers Part 1
1.What is Java?
- Java is a programming language expressly designed for use in the distributed environment of the Internet.
- It was designed to have the "look and feel" of the C++ language, but it is simpler to use than C++ and enforces an object-oriented programming model.
2.What are the various access specifiers for Java classes?
In Java, access specifiers are the keywords used before a class name which defines the access scope. The types of access specifies for classes are:
- Public: Class, Method, Field is accessible from anywhere.
- Protected: Method, Field can be accessed from the same class to which they belong or from the sub-classes, and from the class of same package, but not from outside.
- Default: Method, Field, class can be accessed only from the same package and not from outside of its native package.
- Private: Method, Field can be accessed from the same class to which they belong.
3.What’s the purpose of Static methods and static variables?
When there is a requirement to share a method or a variable between multiple objects of a class instead of creating separate copies for each object, we use static keyword to make a method or variable shared for all objects.
4.What is data encapsulation and what’s its significance?
- Encapsulation is a concept in Object Oriented Programming for combining properties and methods in a single unit.
- Encapsulation helps programmers to follow a modular approach for software development as each object has its own set of methods and variables and serves its functions independent of other objects.
- Encapsulation also serves data hiding purpose.
5.What is a singleton class? Give a practical example of its usage.
- A singleton class in java can have only one instance and hence all its methods and variables belong to just one instance.
- Singleton class concept is useful for the situations when there is a need to limit the number of objects for a class.
- The best example of singleton usage scenario is when there is a limit of having only one connection to a database due to some driver limitations or because of any licensing issues.
6.What are Loops in Java? What are three types of loops?
Looping is used in programming to execute a statement or a block of statement repeatedly.
There are three types of loops in Java:
- For Loops
- While Loops
- Do While Loops
7.What is an infinite Loop? How infinite loop is declared?
An infinite loop runs without any condition and runs infinitely. An infinite loop can be broken by defining any breaking logic in the body of the statement blocks.
8.What is the difference between continue and break statement?
Break and continue are two important keywords used in Loops.
When a break keyword is used in a loop, loop is broken instantly while when continue keyword is used, current iteration is broken and loop continues with next iteration.
9.What is the difference between double and float variables in Java?
- In java, float takes 4 bytes in memory while Double takes 8 bytes in memory.
- Float is single precision floating point decimal number while Double is double precision decimal number.
10.What is Final Keyword in Java?
In java, a constant is declared using the keyword Final.
Value can be assigned only once and after assignment, value of a constant can’t be changed.
In below example, a constant with the name const_val is declared and assigned a value:
Private Final int const_val=100