Core Java Interview Questions and Answers
Introduction to Java Programming
Q:1) The Java interpreter is used for the execution of the source code.
a) True
b) False
Ans: b.
Explain: JVM (Java Virtual Machine) use's
interpreter to convert byte code to machine language at execution
time. So Java interpreter is used to execute byte code not source code.
Q:2) On successful compilation.
A source file will created as .class .
a) True
b) False
Ans: a
Explain: When we compile any file then java complier compile it
and make a class file with same
class extension.
.Q:3)
The Java source code can be created in a Notepad editor
a) True
b) False
Ans: a.
Q:4) The Java Program is enclosed in a class definition
.
a) True
b) False
Ans: a.
Q:5) What declarations are required for every Java application?
Ans: A class and the main( ) method declarations.
Q:6) What are the two parts in executing a Java program and their purposes?
Ans: Two parts in executing a Java program are:
Java Compiler
Java Interpreter.
The Java Compiler is used for compilation and the Java Interpreter is used
for execution of the application.
Q:7) What are the three OOPs principles and define them?
Ans: Encapsulation, Inheritance and Polymorphism are the three
OOPs
Principles.
Encapsulation: Is the Mechanism that binds together code and the data it
manipulates, and keeps both safe from outside interference and misuse.
Inheritance: Is the process by which one object acquires the properties of
another object.
Polymorphism: Is a feature that allows one interface to be used for a
general class of actions.
Q:8) What is a compilation unit?
Ans: Java source code file.
Q:9) What output is displayed as the result of executing the following
statement?
System.out.println("// Looks like a comment.");
1.// Looks like a comment
2. The statement results in a compilation error
3.Looks like a comment
4.No output is displayed
Ans: a.
Q:10) In order for a source code file, containing the public class Test, to
successfully compile, which of the following must be true?
a. It must have a package statement
b.
It must be named Test.java
c.
It must import java.lang
d.
It must declare a public class named Test
Ans: b
Q:11) What are identifiers and what is naming convention?
Ans: Identifiers are used for class names, method names and variable
names. An identifier may be any descriptive sequence of upper case & lower
case letters,numbers or underscore or dollar sign and must not begin with
numbers.
Q:12) What is the return type of program’s main( ) method?
Ans: void
Q:13) What is the argument type of program’s main( ) method?
Ans: string array.
Q:14) Which characters are as first characters of an identifier?
Ans: A – Z, a – z, _ ,$
Q:15) What are different comments?
Ans: 1) // -- single line comment
2) /* --
*/ multiple line comment
3) /** --
*/ documentation
Q:16) What is the difference between constructor method and method?
Ans: Constructor will be automatically invoked when an object is created.
Whereas method has to be call explicitly.
Q:17) What is the use of bin and lib in JDK?
Ans: Bin contains all tools such as javac, applet viewer, awt tool etc.,
whereas Lib contains all packages and variables
Introduction to Java Programming
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