Lecture 2 - Java Basics

Question 1

What is a variable ?

Answer 1

A variable refers to a named storage location, that stores a
value of a particular data type.

A variable has a name (aka identifier), a type, and stores a
value of the declared type.

Question 2

What is the difference between declaring a variable in python and declaring one in java ?

Answer 2

In Java every variable must

be declared as one of the data types before using it.

Question 3

What is a constant ?

Answer 3

It refers to a data item which cannot be changed.

The keyword final must be used in the declaration of a constant. E.g., final int HOURS IN TOTAL=150;

Question 4

Naming conventions for constants ans variables :

Answer 4

Variables: mixed case, lower case first letter E.g., age, buttonColor, dateDue

Constants: all upper case, words separated by underscore. E.g., PI, MIN VALUE, MAX VALUE

Question 5

What primitive datatypes are there in java?

Answer 5

boolean
char
byte 
short 
int
long 
float
double

Question 6

What is the suffix L used for ?

Answer 6

d to indicate it is of type long (e.g.,

234L, OX3E3l). The uppercase L is preferred.

Question 7

int a=012 what is a ?

Answer 7

Because, it’s taken as octal base (8), since that numeral has 0 in leading it’s corresponding decimal value is 10

Question 8

byte d=130;

Answer 8

error because byte accepts values smaller than 128

Question 9

float g = 1.02f;

Answer 9

correct remember to add the small f

Question 10

char h = “B”;

Answer 10

error it needs single brackets ‘B’

Question 11

boolean j = TRUE;

Answer 11

error it needs to be all in small letters

Question 12

What is casting ?

Answer 12

To convert one numeral type to another numeral type ( primitive conversion).

Question 13

What are the two types of casting ?

Answer 13

• Widening (Implicit) : short a=20; long b=a; int c=20; float d=c;
• Narrowing (Explicitly done): long a=20; short b=(short)a; float c=20; int d=(int)c; float hight=(float)0.158;

Question 14

What is overflow?

Answer 14

When an operation with integer types may produce numbers which are too big to be stored in the primitive types you have allocated.