Java Basics Interview Questions

Java Basics Interview Questions

Here are the Interview Questions covering basics of Java,

Q1. Java was initially called what?

A1. Java was called “Oak”, and was given the name “Java.


Q2. When the initial version of Java launched and who originally developed it?

A2. Java was originally developed by James Gosling and was initially released in 1995


Q3. Define JAVA?

A3. Java is an object oriented programming language, which is platform independent. It was developed in 1995 and acquired by Oracle in 2010.


Q4. State the Java Versions?

A4.

Here are the Java Versions,

Java Release Release Year
JDK 1.01996
JDK 1.11997
J2SE 1.21998
J2SE 1.32000
J2SE 1.42002
J2SE 1.52004
Java SE 62006
Java SE 72011
Java SE 82014
Java SE 92017

Q5. State some applications of Java?

A5.

  • 100+ TV Devices run Java
  • 3 Billion Mobile Phones run Java
  • Game consoles
  • Refer for more: applications of Java!

Q6. Java addresses the following well-known issues of Internet?

A6. Portability and Security are the major issues with Internet. Java came at the time when WWW came to light. The Internet required a portable programming language to address its issues.


Q7. State how Java solves the issue of Portability and Security?

A7. Java solves the issue of Portability and Security since the output of a Java compiler is Bytecode, not executable code.


Q8. What is Bytecode?

A8. The set of instructions designed to be executed by the Java run-time system is Bytecode. Here, the set of instructions are highly optimized and the Java run-time system is called the Java Virtual Machine (JVM).


Q9. What is Java Virtual Machine (JVM)?

A9. Java Virtual Machine (JVM) provides runtime environment in which Java bytecode can be executed


Q10. Why a Java program is translated to Bytecode?

A10. The translation makes it easier to run a program in different environments. This is because only the JVM needs to be implemented for each platform.


Q11. Does Java support Remote Method Invocation (RMI)?

A11. Yes, Java supports Remote Method Invocation, which is a Java API. The Java RMI API performs remote method invocation i.e. enable a program to invoke methods across a network.


Q12. List some of the new feature introduced in Java SE 8 (Java 8)?

A12. The new features are:

  • Lambda Expressions
  • New Stream API
  • Package java.util.function introduced.
  • New Time and Date API
  • Supports for JavaFX 8

Q13. How Java is Architecture-Neutral?

A13. Java is Architecture Neutral, since it is platform independent i.e. it follow:

write once; run anywhere, anytime, forever

A Java program do not depend on the operating system you have or the hardware, even it do not
get affected by Operating System upgrades, ro changes in system resources.


Q14. Which of the following would create a class file “SampleProgram.class” after execution,

1.) Compile time statement – javac SampleProgram.java

2.) Runtime statement – java SampleProgram

A14. Compile time statement – “javac SampleProgram.java” will create a class file “SampleProgram.class”. javac is Java Compiler that creates a class file of a java program as shown above.


Q15. The Java compiler requires that a source file use the “.java” filename extension. True or false?

A15. True, as shown in Q14 above, we compiled a file named “SampleProgram.java”


Q16. Are Java file names case-sensitive? True or False?

A16. True


Q17. A Java program begins with a call to which function?

A17. Java program begins with a call to main() function.


Q18. What are the three styles of comments Java supports?

A18. Java supports the following three styles of comments,

  • Single-line comment
  • Multi-line comment
  • Documentation comment

Q19. What does “public” mean in the following,

A19. public is a keyword, which is an access modifier


Q20. What does “static” mean in the following,

A20. static is a keyword that allows calls main( ) method without the need to instantiate a particular instance of the class.


Q21. What is the usage of “args[ ]” parameter in the following,

A21. String args[ ] is an array of instances. Here, the args receives any command-line arguments. These arguments can be worked upon when the program is executed. For example,

          java SampleProgram.java arg1

Here, arg1 is argument one


Q22. What is System.out.println in the following sample program,

A22. Here,

  • System = predefined class
  • out = output stream
  • println = It is a method that  prints message, in this case it prints “Our first Java Program”

Q23. Java programs are a collection of ________?

A23. Whitespace, identifiers, literals, comments, operators, separators, & keywords


Q24. What is Whitespace?

A24. Space, tab, or newline added to a Java program is known as whitespace.


Q25. Define Identifiers?

A25. Identifiers are the name given to a class, method and variables.
For example: temp, i, count1, count2 are all Identifiers.


Q26. Give examples of Literals in Java?

A26.  Here are three examples showing floating-point, integer, and string literals:

  • 32.7
  • 10
  • Java is awesome!

Q27. Java 8 has added two new operators? Name it?

A 27. The two new operators added in Java 8 are,
1.) :: i.e. Double Colon
2.) Lambda Expressions


Q29. Explain the usage of Double Colon operator introduced in Java 8.

A29.  The :: i.e. double colon operator has been added in Java8, and used to create reference to a method or constructor.


Q30. List some Java Keywords?

A30.  Here are some Java keywords:
Boolean, break, int, float, extends, package, this, throws, void, native, volatile, transient, etc.


Q31. Is Java a Strongly Typed language?

A31. Yes


Q32. List all the primitive types of data (data type) in Java?

A32. Here are the primitive types of data in Java: boolean, byte, int, short, long, char, float, double


Q33. Name the smallest integer type?

A33.  Byte is the smallest integer type


Q34. Which one is a signed 16-bit type,

a.) int
b.) short
c.) long

A34.  short


Q35. Which one is a signed 32-bit type,

a.) int
b.) short
c.) long

A35. int


Q36. Which type is used for huge, whole numbers? For example, 178685726876

a.) int
b.) long
c.) short

A36.  Such huge numbers could only be handled by long type.


Q37. Name the two floating-point types?

A37. The floating-point types are double and float.


Q38. When double-type is preferred over float-type?

A38.  When you need a large degree of precision and large-valued numbers, and then use double-type.
For example, transcendental math functions like sin( ), cos( ), and sqrt( ), return double values.

Double-type uses 64 bits to store a value, unlike float, which uses only 32 bits to store a value.


Q39. Are chars in C/C++ are same as chars in Java?

A39.  C/C++: char is a 8-bit type.

Java: char is a 16-bit type.


Q40. State the difference between chars in Java and char in C/C++?

A40. char in Java:

  • char is a 16-bit type in Java and uses Unicode, which is a unification of characters
    sets to represent characters.
  • Range from 0 to 65,536
  • No negative chars.

          char in C/C++:

  • char is a 8-bit type in  C/C++ and the characters are represented by ASCII,
  • Range from -128 to 127 or 0 to 255

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