Java Viva Voce -2

1. What is a variable?

Name which refers memory locations and it can hold a value which can be changed at runtime is called Variable.

2. What are primitive data types?

A primitive type is predefined by the language and is named by a reserved keyword.

3. How many primitive data types are there in Java?

There are 8 primitive data types and they are byte, int, short, long, float, double, char and Boolean.

4. Does Java has any unsigned types?

No, Java does not have any unsigned types.

5. What do the floating-point numbers without an F suffix indicate?

Floating-point numbers without an F suffix indicate to be of type double. We can optionally supply the D suffix also (ex. 3.402D).

6. What are identifiers?

Identifiers are the names of variables, methods, classes, packages and interfaces. Unlike literals they are not the things themselves, just ways of referring to them.

7. Why do we use Unicode in Java?

Most of the countries now use Unicode so we use them in Java too.

8. What is Escape sequence for special character in Java? List some of them.

A character preceded by a backslash (\) is an escape sequence and has special

meaning to the compiler. \b, \t, \n, \r etc. are some escape sequences in Java.

9. Can you use a Java reserved word for a variable name?

No, we cannot use a Java reserved word for a variable name.

10. Why do we use the keyword final in Java?

In Java, you use the keyword final to denote a constant. The keyword final indicates that you can assign to the variable once, and then its value is set once and for all. It is compulsory to name constants in all uppercase.

11. How can you avoid the Math prefix for the mathematical methods and constants?

By importing the package:

 import static java.lang.Math.*; we can avoid the Math prefix for the mathematical methods and constants.

12. Does Java has built in String type?

 Java does not have a built-in string type. Instead, the standard Java library contains a predefined class called String.

13. how is Instance variable declared?

Instance variables are created when an object is created with the use of the keyword 'new' and destroyed when the object is destroyed.

14. What is the difference between class variable and instance variable?

An instance variable is a variable which has one copy for an object.
A class variable is a variable which has one copy per class. The class variables will not have a copy in the object.

15. What are the default values for numbers, Boolean values and Object references?

For numbers, the default value is 0, for Booleans it is false and for object references it is null.

16. What is naming convention?

Java naming convention is a rule to follow as you decide what to name your identifiers such as class, package, variable, constant, method etc.

 17. What is the naming convention used for a class and a method?

Class name should start with an Uppercase and method name should start with Lowercase.

18. What is Literals?

A literal is a value assigned to a variable or a constant is called a literal. Java language specifies five major types of literals: Integer literals, Floating literals, Character literals, String literals, Boolean literals.

19. What is Type casting?

When the data is converted from one data type to another data type, then it is called type casting. Type casting is nothing but changing the type of the data.

20.  What are the types of casting?

There are two types of casting.

             1) Primitive Casting: When the data is casted from one primitive type (like int, float,                          double etc…) to another primitive type, then it is called Primitive Casting.

            2) Derived Casting: When the data is casted from one derived type to another derived type, then it is called derived casting.

21. What is precedence of java operators?

Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated.  For example, the multiplication operator has higher precedence than the addition operator.

22. What are Control flow statements?

Control flow statements, however, break up the flow of execution by employing decision making, looping, and branching, enabling your program to conditionally execute particular blocks of code.

23. What are Branching Statements?

Break, continue and return are Branching statement.

24. Why do we use continue statement?

You use the continue statement to skip the current iteration of a for, while , or do-while loop.

25. Why do we use loops in program?

A loop statement allows us to execute a statement or group of statements multiple times which reduces the size of program.

26.  What are access modifiers in java?

These are the modifiers which are used to restrict the visibility of a class or a field or a method or a constructor.

27. How many access modifiers are there in Java?

Java supports 4 access modifiers.

a) Private: private fields or methods or constructors are visible within the class in which they    are defined.

b) Protected: Protected members of a class are visible within the package but they can be inherited to sub classes outside the package.

c) Public: public members are visible everywhere.

d) Default or No-access modifiers: Members of a class which are defined with no access modifiers are visible within the package in which they are defined.

28. Can we declare a class as protected?

We can’t declare an outer class as protected but we can declare an inner class (class as a member of another class) as protected.

29.  What are non-access modifiers in java?

These are the modifiers which are used to achieve other functionalities like static, final, abstract.

30. What is Class and Object?

A class is a program construct which encapsulates data and operations on data. In object oriented programming, the class can be viewed as a blue print of an object. An object is a program construct that falls under a ‘classification’ (of a class) which has state and behavior.

31. How to create an object in a Java Program?

There are three steps to create an object from a class −

Declaration − A variable is declared with an object type.

Instantiation − the 'new' keyword is used to create the object.

Initialization − the 'new' keyword is followed by a call to a constructor. This call initializes the new object.

32. What is a method?

A method (function) is a collection of statements that are grouped together to perform an operation.

33. What is constructor?

Constructor is a special type of method that is used to initialize the object. Java constructor is invoked at the time of object creation.

34. How many types of constructors are there in java?

There are two types of constructors:

Default constructor (no-argument constructor), Parameterized constructor.

35.  What is Constructor Overloading?

Constructor overloading is a technique in Java in which a class can have any number of constructors that differ in parameter lists.

36. What is Garbage Collection?

Garbage Collection is process of reclaiming the runtime unused memory automatically. In other words, it is a way to destroy the unused objects.

37.  What is the advantage of Garbage Collection?

It makes java memory efficient because garbage collector removes the unreferenced objects from heap memory.

38. What is finalize method?

The finalize method is invoked each time before the object is garbage collected. This method can be used to perform cleanup processing.

39. What is static keyword?

The static keyword in java is used for memory management mainly. We can apply java static keyword with variables, methods, blocks and nested class.

40. What is a static variable?

If you declare any variable as static, it is known static variable. The static variable can be used to refer the common property of all objects.

41. What is static method?

If you apply static keyword with any method, it is known as static method.

42.What is java command line argument?

Java command line argument is an argument i.e. passed at a time of running the java program.

43. Where the arguments are received and used?

The arguments passed from the console can be received in the java program and it can be used as an input.

44.How the arguments are useful?

They provide a convenient way to check the behaviour of the program for different values.

45.What is an ARRAY?

An array stores the fixed size sequential collection of elements of the same type.

46.How is an array used?

An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of same data type.

47.What is for each loop also known as?

Enhanced for loop.

48.What is the use of for each loop?

It enables us to traverse the complete array sequentially without using an index variable.

49.What is an ARRAY CLASS?

This class contains various static methods for sorting and searching arrays, comparing and filling array elements.

50.What is This keyword in java?

THIS keyword is used as a reference to the object of the current class, with in an instance method or a constructor.

51.What is use of this keyword?

Differentiate the instance variables from local variables if they have some names, within a constructor or a method.

52.  Can we call method with this keyword from constructor?
           Yes, we can call non static methods from constructor using this keyword.

53. Is it possible to assign reference to this?

No we cannot assign any value to "this" because it’s always points to current object      and it is a final reference in java. If we try to change or assign value to this compile time error will come.

54. Can we use this in static methods? 

No we cannot use this in static methods. if we try to use compile time error will come: Cannot use this in a static context.