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Java Objectives - Part 1

The reason for documenting this topic is to provide important technical questions and answers on Java language.  These questions can appear in an aptitude test, organized by different recruiting IT organizations.

 

Important questions and their answers are as under:

1) The Java  interpreter is used for the execution of the source code.

a) True

b) 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 OOP’s 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.");

a) // Looks like a comment

b) The statement results in a compilation error

c) Looks like a comment

d) 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?

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

 

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.

 

Some Questions on Data types, Variables and Arrays:

 

1) What is meant by variable?

Ans: Variables are locations in memory that can hold values. Before assigning any value to a variable, it must be declared.

 

2) What are the kinds of variables in Java? What are their uses?

Ans: Java has three kinds of variables namely, the instance variable, the local variable and the class variable.

Local variables are used inside blocks as counters or in methods as temporary variables and are used to store information needed by a single method.

Instance variables are used to define attributes or the state of a particular object and are used to store information needed by multiple methods in the objects.

Class variables are global to a class and to all the instances of the class and are useful for communicating between different objects of all the same class or keeping track of global states.

 

3) How are the variables declared?

Ans: Variables can be declared anywhere in the method definition and can be initialized during their declaration. They are commonly declared before usage at the beginning of the definition.

Variables with the same data type can be declared together. Local variables must be given a value before usage.

 

4) What are variable types?

Ans: Variable types can be any data type that java supports, which includes the eight primitive data types, the name of a class or interface and an array.

 

5) How do you assign values to variables?

Ans: Values are assigned to variables using the assignment operator =.

 

6) What is a literal? How many types of literals are there?

Ans: A literal represents a value of a certain type where the type describes how that value behaves.

There are different types of literals namely number literals, character literals, boolean literals, string literals, etc.

 

7) What is an array?

Ans: An array is an object that stores a list of items.

 

8) How do you declare an array?

Ans: Array variable indicates the type of object that the array holds.

Ex: int arr[];

 

9) Java supports multidimensional arrays.

a) True

b) False

Ans: a.

 

10) An array of arrays can be created.

a) True

b) False

Ans: a.

 

11) What is a string?

Ans: A combination of characters is called as string.

 

12) Strings are instances of the class String.

a) True

b) False

Ans: a.

 

13) When a string literal is used in the program, Java automatically creates instances of the string class.

a) True

b) False

Ans: a.

 

14) Which operator is to create and concatenate string?

Ans: Addition operator(+).

 

15) Which of the following declare an array of string objects?

a) String[ ] s;

b) String [ ]s:

c) String[ s]:

d) String s[ ]:

Ans : a, b and d

 

16) What is the value of a[3] as the result of the following array declaration?

a) 1

b) 2

c) 3

d) 4

Ans : d

 

17) Which of the following are primitive types?

a) byte

b) String

c) integer

d) Float

Ans : a.

 

18) What is the range of the char type?

a) 0 to 216

b) 0 to 215

c) 0 to 216-1

d) 0 to 215-1

Ans. d

 

19) What are primitive data types?

Ans : byte, short, int, long

float, double

boolean

char

 

20) What are default values of different primitive types?

Ans : int - 0

short - 0

byte - 0

long - 0 l

float - 0.0 f

double - 0.0 d

boolean - false

char - null

 

21) Converting of primitive types to objects can be explicitly.

a) True

b) False

Ans: b.

 

22) How do we change the values of the elements of the array?

Ans : The array subscript expression can be used to change the values of the elements of the array.

 

23) What is final varaible?

Ans : If a variable is declared as final variable, then you can not change its value. It becomes constant.

 

24) What is static variable?

Ans : Static variables are shared by all instances of a class.

 

 

Some questions and answers on operators:

 

1) What are operators and what are the various types of operators available in Java?

Ans: Operators are special symbols used in expressions.

The following are the types of operators:

Arithmetic operators,

Assignment operators,

Increment & Decrement operators,

Logical operators,

Biwise operators,

Comparison/Relational operators and

Conditional operators

 

2) The ++ operator is used for incrementing and the -- operator is used for

decrementing.

a) True

b) False

Ans: a.

 

3) Comparison/Logical operators are used for testing and magnitude.

a) True

b) False

Ans: a.

 

4) Character literals are stored as unicode characters.

a) True

b) False

Ans: a.

 

5) What are the Logical operators?

Ans: OR(|), AND(&), XOR(^) AND NOT(~).

 

6) What is the % operator?

Ans : % operator is the modulo operator or reminder operator. It returns the reminder of dividing the first operand by second operand.

 

7) What is the value of 111 % 13?

a) 3

b) 5

c) 7

d) 9

Ans : c.

 

8) Is &&= a valid operator?

Ans : No.

 

9) Can a double value be cast to a byte?

Ans : Yes

 

10) Can a byte object be cast to a double value ?

Ans : No. An object cannot be cast to a primitive value.

 

11) What are order of precedence and associativity?

Ans : Order of precedence the order in which operators are evaluated in expressions.

Associativity determines whether an expression is evaluated left-right or right-left.

 

12) Which Java operator is right associativity?

Ans : = operator.

 

13) What is the difference between prefix and postfix of -- and ++ operators?

Ans : The prefix form returns the increment or decrement operation and returns the value of the increment or decrement operation.

The postfix form returns the current value of all of the expression and then

performs the increment or decrement operation on that value.

 

14) What is the result of expression 5.45 + "3,2"?

a) The double value 8.6

b) The string ""8.6"

c) The long value 8.

d) The String "5.453.2"

Ans : d

 

15) What are the values of x and y ?

x = 5; y = ++x;

Ans : x = 6; y = 6

 

16) What are the values of x and z?

x = 5; z = x++;

Ans : x = 6; z = 5

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