OOP_Assignment 1.docx

Assignment Chapter 2: Elementary Programming

There is an error in the codes above which is in line number 2. The main method of the codes is

not declared as static. Main method should be declared as public, static and void in Java.

Output when the main method declared as public void main (string [ ] args) is below;

Figure 1 : Error when main method is not declared as static

Otherwise when the main method is declared as public static void main (string [ ] args), the

output will be as below;


In order to let the user enter a double value from the keyboard, we need to import

“java.util.Scanner” followed by the statement below in the main ;

Scanner myinput = new Scanner(System.in);

double value = myinput.nextDouble( );

There would be an error telling that we have entered a mismatch input. This is because ‘5a’

contains of a character ‘a’. If we just enter ‘5’ then the program will run without error.

Figure 2 : Error when user entered input with different data type


The “import java.util.Scanner;” is called as specific import and the “import java.util.*;” is called as wildcard import declaration.

miles = valid

Test = valid

a++ = invalid because it is an operator that show post-increment

--a = invalid because it is an operator that show pre-decrement

4#R = invalid because it consists an illegal character which is ‘#’

$4 = valid

#44 = invalid because it consists an illegal character which is ‘#’

apps = valid

class = invalid because it is a java keyword

public = invalid because it is a java keyword

int = invalid because it is a java keyword

x = valid

y = valid

radius = valid


The error is in line 3. The variable ‘k’ is not declared in the code. To fix the error, the variable

‘k’ must be declared and initialized to a value before line 3.

The error is in line 3. The variable ‘j’ and ‘k’ are not declared. To fix the error, the variable ‘j’

and ‘k’ must be declared before the line number 3.


i. You don’t have to repeatedly type the same value if it is used multiple times.

ii. If you have to change the constant value, you need to change it only in a single

location in the source code.

iii. A descriptive name for a constant makes the program easy to read.

int SIZE = 20 ;

Naming Conventions

Class Capitalize the first letter of each word in a class name.

E.g. ComputeArea and System.

Method Use lowercase for methods. If a name consists of several words, concatenate

them into one, making the first word lowercase and capitalizing the first letter

of each subsequent word.

E.g. print.

Constants Capitalize every letter in a constant, and use underscores between words.

E.g. PI and MAX_VALUE.

Variables Use lowercase for variables. If a name consists of several words, concatenate

them into one, making the first word lowercase and capitalizing the first letter

of each subsequent word.

E.g. radius and area.

MAX_VALUE = Constant

Test = Class

read = Method

readDouble = Variable


The data types that requires the least amount of memory is byte 8-bit storage size.


Since the remainder of 100/7 is 2, therefore we just need to find the 2 days after Tuesday. So the

answer will be Thursday.


To get the result as a floating-point number, we can rewrite the expression as below:


A float value has 7 to 8 number of significant digits and a double value has 15 to 17 number of

significant digits.


12.3 = Not a floating-point number (double)

12.3e+2 = Floating-point number

23.4e-2 = Floating-point number

-334.4 = Not a floating-point number (double)

20.5 = Not a floating-point number (double)

39F = Floating-point number

40D = Not a floating-point number (double)

5.2534e+1 = 52.534 (Same)

0.52534e+2 = 52.534 (Same)

525.34e-1 = 52.534 (Same)

5.2534e+0 = 5.2534 (Not the same)

5_2534e+1 = Correct

_2534 = Incorrect

5_2 = Correct

5_ = Incorrect


a. (4 / (3*(r+34))) - 9(a+b*c) + (3+d*(2+a))/(a+b*d)

b. 5.5*Math.pow(r+2.5,2.5+t)


a. True

b. True

c. True

d. False


When the arithmetic expression in line 11 changed to (int)(tax*100)/100, the result will be

returned in integer instead of double/float number.

OOP_Assignment 1.docx

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