Learn how to use data, variables and expressions and how to perform simple calculations in Java.

1. Java Tutorial
Part 4: Data and
Calculations

2. Variables
Storing and
Processing Data
in the Memory

3.  Computers are machines that process data
 Both program instructions and data are stored in
the computer memory
 Data is stored by using variables
How Does Computing Work?
10110

4.  A variable is a container for information
 A named area of the computer memory
 The data can be read and changed at any time
 Variables provide means for:
 Storing data
 Retrieving the stored data
 Modifying the stored data
Variables

5.  Variables are characterized by:
 name (identifier)
 type (of the data preserved)
 value (stored information)
 Defining a variable in Java:
Variables
int age = 25;
Data
type
Variable
name
Variable
value
Name Type Value
age int 25
name String "Peter"
size double 3.50
Computer memory

6. Data Types
Text, Numbers,
and Other
Types in Java

7.  Variables store value of a certain type
 Number, letter, text (string), date, color, picture, list, …
 Data types:
 int – an integer: 1, 2, 3…
 double – a floating-point number: -0.5, 3.14, …
 boolean – a boolean: true, false
 char – a symbol: 'a', 'b', '#', …
 String – text: "Hello", "World", …
Data Types

8.  Data types define ranges of values with similar
characteristics
 Data types are characterized by:
 Name
 Example: boolean, int, String
 Size (memory usage)
 Example: 4 bytes
 Default value
 Example: 0
Data Types (2)

9. Statements
Commands in the
Computer Programs

10.  The actions that a program takes, are expressed as statements
 Common statements (actions / commands) include:
 Declaring a variable
 Assigning a value
 Declaring + initializing
Statements
int counter;
counter = 1;
int counter = 1;
 Printing a value
System.out.println(counter);
 Modifying a value
counter++;
sum = a + b;

11.  If-else statement
 Method definition statement
Complex Statements
if (a == 5)
System.out.println("Five");
else
System.out.println("Not Five");
 Loop statement
int a = 5;
while (a > 0) {
a--;
}
static int sum(int a, int b) {
return a + b;
}

12. Arithmetic Operators
Add, Subtract, Multiply
and Divide Numbers
+ -
* /

13.  Adding numbers (operator + )
 Subtracting numbers (operator - )
Arithmetic Operators: + and -
int a = 5;
int b = 7;
int sum = a + b;
System.out.println(sum); // 12
int a = 15;
int b = 7;
System.out.println(a - b); // 8

14.  Multiplying numbers (operator *)
 Dividing numbers (operator / )
Arithmetic Operators: * and /
int a = 5;
int b = 7;
System.out.println(a * b); // 35
int a = 25;
int b = 4;
System.out.println(a / b); // 6

15.  When dividing integers, the result is also integer:
 When dividing floating-points, the result is also floating-point:
Division Behavior in Java
int a = 25;
System.out.println(a / 4); // Integer result: 6
System.out.println(a / 0); // Error: division by 0
double a = 15;
System.out.println(a / 2.0); // 7.5
System.out.println(a / 0.0); // Infinity
System.out.println(0 / 0.0); // NaN

16.  Modulo / remainder from integer division (operator % )
Arithmetic Operators: %
int a = 7;
int b = 2;
System.out.println(a % b); // 1
System.out.println(3 % 2); // 1
System.out.println(4 % 2); // 0
System.out.println(3.5 % 1); // 0.5
7 = 3 * 2 + remainder 1
3 = 1 * 2 + remainder 1
4 = 3 * 2 + remainder 0
3.5 = 3 * 1 +
remainder 0.5

17. Expressions
Calculations with
Values and Operators
(a+b)
*c -1

18.  Expressions == sequences of operators, literals and
variables which are evaluated to a value
 Consist of at least one operand
 Can have 1 or more operators
Expressions
int r = (150-20) / 2 + 5;
int y = x + 5;
String name = "John Doe";

20.  Write a program to convert from USD to EUR:
 Read a floating-point number: the dollars to be converted
 Convert dollars to euro (use fixed rate of dollars to euro: 0.88)
 Print the converted value in euro formatted to the 2nd digit
Problem: Currency Converter
17 14.96
87 76.56
Judge: https://judge.softuni.org/Contests/Practice/Index/3253

21. Creating a New Project in IntelliJ IDEA

22. Solution: Currency Converter
Scanner scanner = new Scanner(System.in);
double dollars = scanner.nextDouble();
double euros = dollars * 0.88;
System.out.printf("%.2f", euros);

23. Submission in the Judge System
https://judge.softuni.org/Contests/Practice/Index/3253

24.  Write a program, which:
 Reads 2 real numbers from the console
 Performs 4 arithmetic operations on the obtained
2 numbers, in the following order: +, -, *, /
 Formats and prints the results like this example:
Problem: Four Operations
5
10
5.00 + 10.00 = 15.00
5.00 - 10.00 = -5.00
5.00 * 10.00 = 50.00
5.00 / 10.00 = 0.50

25. Solution: Four Operations
double num1 = Double.parseDouble(sc.nextLine());
double num2 = Double.parseDouble(sc.nextLine());
double sum = num1 + num2;
System.out.printf("%.2f + %.2f = %.2fn",
num1, num2, sum);
// TODO: Implement the rest of operations
Denotes a
new line

26.  …
 …
 …
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