Library Classes

Question 1

define package

Answer 1

a package is a collection of classes containing different built-in function

Question 2

what is java.awt used for

Answer 2

contains classes to implement Graphical User Interface

Question 3

what does the asterisk (*) sign indicate

Answer 3

that all the classes of the imported package can be used in a program

Question 4

define primitive data types

Answer 4

fundamental or basic data types which are created by the system developers.

Question 5

define composite data types

Answer 5

it is a set of primitive data types

Question 6

what is Wrapper Class

Answer 6

a built-in data type, composite, is called wrapper class

Question 7

function of Integer.parseInt()

Answer 7

to convert a string into integer data type

Question 8

function of Integer.toString()

Answer 8

convert integer data type to string

Question 9

need of wrapper class

Answer 9

1. store primitive values in objects
2. to convert a string to other data types, and vice versa

Question 10

general syntax for converting string to primitive data types

Answer 10

1. <primitive> variable= <wrapperclass>.parse<datatype>(String argument);
   </datatype></wrapperclass></primitive>
2. <primitive> variable= <wrapperclass>.valueOf(String argument);
   
   </wrapperclass></primitive>

int x= Integer.parseInt(s1)
int x= Integer.valueOf(s1)

Question 11

condition for conversion from string to primitive data type

Answer 11

only when the string contains only numbers.
if letters are used, then java throws NumberFormatException error

Question 12

general syntax for primitive data type to string

Answer 12

String variable== Integer.toString(int argument);

Question 13

how many ASCII characters are there

Answer 13

256, but only 128 characters are used

Question 14

ASCII for 0-9

Answer 14

48-57

Question 15

ASCII for A-Z

Answer 15

65-90

Question 16

ASCII for a-z

Answer 16

97-122

Question 17

ASCII for blank space

Answer 17

32

Question 18

syntax for inputting character through scanner class

Answer 18

char ch= sc.next().charAt(0);

Question 19

syntax of inputting character through InputStreamReader

Answer 19

InputStreamReader read= new InputStreamReader(System.in);
BufferedReader in= new BufferedReader(read);
char ch= (char)(in.read());

Question 20

what is Character.isLetter(character) used for

Answer 20

to check whether a character is a letter or not

Question 21

what is Character.isLetterOrDigit(char) used for

Answer 21

if a character is a letter or digit, it returns true. otherwise, returns false.

Question 22

how to convert uppercase character to lowercase using ASCII

Answer 22

1.get ASCII of uppercase character
2. increase ASCII by 32
3. convert back to char form, for corresponding letter

vice versa for lowercase to uppercase

Question 23

define autoboxing

Answer 23

the automatic conversion of a primitive data type into an object of its equivalent Wrapper class is called Autoboxing

Question 24

syntax of autoboxing

Answer 24

<wrapper> <objectname>= new (wrapper class>(Primitive value);
Integer val= new Integer(54);
</objectname></wrapper>

Question 25

need for autoboxing

Answer 25

1. to pass a primitive data type to a function that uses wrapper object as function argument
2. add a primitive data in the list of array elements

Question 26

define unboxing

Answer 26

system of converting an object of wrapper class into primitive data type. it is the opposite of autoboxing.

Question 27

need for unboxing

Answer 27

1. to pass a value from wrapper object to a function have argument as primitive
2. when a data from array list is to be used as primitive data types.