Crack Java Job Interview in 2021
Here in this article, we have mentioned the frequently asked Java Interview Questions and Answers. With the increment in the flow of interview questions, difficulty raise too.
What is Java?
Answer: Java is a general-purpose high-level, object-oriented programming language that works on the principle “write once and run anywhere”. It was developed by James Gosling in 1991 at Sun Microsystems later bought by Oracle Corporation.
What is Core Java?
Answer: When Oracle bought Java, they give their own definition to it and release a Java Standard Edition which is commonly known as Java. The core Java deals with the basic type and Object of Java Programming.
What is the latest version of Java?
Answer: Java SE 17 is the latest version of Java that comes with Long Term Support (LTS).
The next Java versions tentative release dates are
- Java Versions Release Date
- Java SE 18 March 2022
- Java SE 19 September 2022
- Java SE 20 March 2023
- Java SE 21 (LTS) September 2023
What is JVM?
Answer: JVM is an acronym for Java Virtual Machine. JVM is one of the parts of the Java Runtime Environment (JRE). It is the one which calls the Main method of Java Code.
How does a bytecode run in JAVA?
Answer: Bytecode is a compiled format of a java program. Classloader loads the bytecode into a java runtime environment where the JIT compiler converts bytecode into machine-dependent code.
What is Thread in Java?
Answer: The flow of execution is referred to as a thread. The main which is used in every java program is also a thread. This main thread is created by JVM. The user can create their own thread by extending the thread class.
Why do we declare Main as Static?
Answer: Main is the entry point of the program hence it is declared as static. For calling the static method we never need an object of a class.
What is Super Keyword in JAVA and Where to use it?
Answer: If superclass and subclass both have the same method as well as the variable name, to identify superclass variables & methods in the subclass, a super keyword is used. It is always written in the subclass only when the method name is the same. It is used to class superclass constructors explicitly.
When a subclass has only parameterized constructor and a superclass does not have a matching constructor, What will happen?
Answer: A default constructor of the superclass will get invoked when a subclass has only parameterized constructor and the superclass does not have any matching constructor.
If the superclass has parameterized constructor and the subclass wants to use that constructor then we must write the “super” keyword to pass parameters in the superclass constructor.
The super keyword must be written in the very first line in the constructor of the subclass.
Explain Public Static Void Main (String args[]).
Answer:
Access modifier is also known as Access specifiers. Access modifiers in Java have clarified the classes which can access a given class and its fields, constructors, and methods.
- Public: A type of access modifier. It is used to specify who can access this method. This means that this method can be accessed by any class.
- Static: It is a keyword in java that identifies it can be accessed without creating the instance of a Class.
- Void: Void is a return type of method that will not return any value.
- Main: It is referred to as a method that is searched by JVM as a starting point for an application with a particular signature only.
- String args[]: It is a parameter that is passed to the main method.
What are Constructors in Java?
Answer: In Java, Constructors are the block of codes that are similar to a method. A constructor is called when an instance of an object is created. The name of the constructor is kept the same as the name of the class. There is no return type of a constructor, not even void. If we don’t create an explicit constructor in our class, the java compiler supplies it by default.
What do you understand by a Wrapper class?
Answer: A wrapper class is a class that converts java primitives into reference-type objects. They “wrap” the primitive data type into an object of that class, therefore they are referred to as wrapper class.
Explain the local variable and instance variable?
Answer: Local variables are defined inside methods and constructors. Instance variables are those variables that are present within a class but outside any method.
Why JAVA is a statically typed language?
Answer: Java is referred to as a statically typed language as the type of the variable is known at the compile time.
What is Java Runtime Environment(JRE)?
Answer: JRE is the abbreviation of the Java Runtime Environment. It is an environment in which bytecode runs. In other words, JRE is a software package that has everything that needs to run a Java Program.