Top Most Basic Java Faq's

1.The Java interpreter is used for the execution of the source code.
True
False
Ans: a. 

2) On successful compilation a file with the class extension is created.
a) True
b) False
Ans: a.

3) The Java source code can be created in a Notepad editor.
a) True
b) False
Ans: a.

4) The Java Program is enclosed in a class definition.
a) True
b) False
Ans: a.

5) What declarations are required for every Java application?
Ans: A class and the main( ) method declarations.

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 and Java Interpreter.
The Java Compiler is used for compilation and the Java Interpreter is used for execution of the application.

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.


8) What is a compilation unit?
Ans : Java source code file.

9) What output is displayed as the result of executing the following statement?
System.out.println("// Looks like a comment.");
// Looks like a comment
The statement results in a compilation error
Looks like a comment
No output is displayed
Ans : a.

10) In order for a source code file, containing the public class Test, to successfully compile, which of the following must be true?
It must have a package statement
It must be named Test.java
It must import java.lang
It must declare a public class named Test
Ans : b

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.

12) What is the return type of program’s main( ) method?
Ans : void

13) What is the argument type of program’s main( ) method?
Ans : string array.

14) Which characters are as first characters of an identifier?
Ans : A – Z, a – z, _ ,$

15) What are different comments?
Ans : 1) // -- single line comment
2) /* --
*/ multiple line comment
3) /** --
*/ documentation

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.

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.