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01 Java Fundamentals (variables, data types, operators)

1 Variables

A variable in Java is a container that holds a value. It has a name and a specific data type.

Definition: A variable is a named storage location in a program’s memory that can hold different values during the execution of the program.

Example:

    int age = 25;
    String name = "John Doe";

2 Data Types

A data type defines the kind of data a variable can hold and the operations that can be performed on it.

Java has two categories of data types:

Primitive Data Types
Reference Data Types

2.1 Primitive Data Types:

byte: Stores a single byte of data (-128 to 127)
short: Stores a two-byte integer (-32768 to 32767)
int: Stores a four-byte integer (-2147483648 to 2147483647)
long: Stores an eight-byte integer (-9223372036854775808 to 9223372036854775807)
float: Stores a single-precision floating-point number (32 bits)
double: Stores a double-precision floating-point number (64 bits)
char: Stores a single character (Unicode character)
boolean: Stores a boolean value (true or false)

    // example of primitive data type
    byte myByte = 127;
    int myInt = 1000000;
    double myDouble = 3.14159;
    boolean isJavaFun = true;
    char myChar = 'A';

2.2 Reference Data Types

String: Represents a sequence of characters.
Array: Stores a collection of elements of the same data type.
Classes and Objects: Represent real-world entities

    String greeting = "Hello, World!";
    int[] numbers = {1, 2, 3, 4, 5};
    MyClass obj= new MyClass();

3 Operators

Operators are symbols that perform operations on variables and values.

Arithmetic Operators: +, -, *, /, %, ++, –
Relational Operators: ==, !=, >, <, >=, <=
Logical Operators: && (and), (or), ! (not)
Assignment Operators: =, +=, -=, *=, /=, %=
Bitwise Operators: &, , ^, ~, «, », »>
Ternary Operator: condition ? ifTrue : ifFalse;

3.1 Arithmetic Operators:

    + (addition)
    - (subtraction)
    * (multiplication)
    / (division)
    % (modulo - remainder)
    ++ (increment)
    -- (decrement)

Example:

    int a = 10;
    int b = 3;
    int sum = a + b;  // 13
    int difference = a - b;  // 7
    int product = a * b;  // 30
    int quotient = a / b;  // 3
    int remainder = a % b;  // 1

increment and decrement operator postfix and prefix are not equivalent

    int a=10,b=20,c=10,d=20;
    int incrementA = a++; // a becomes 11, incrementA is 10
    int decrementB = b--; // b becomes =19, decrementB is 20
    int incrementC= ++c; //  c becomes 11, incrementC  is 11
    int decrementD= --d; // d becomes 19m decrementB is 19

3.2 Relational Operators

also call Comparison Operators

    == (equal to)
    != (not equal to)
    > (greater than)
    < (less than)
    >= (greater than or equal to)
    <= (less than or equal to)

Example

    boolean isGreater = 10 > 5; // Comparison

    int x = 5;
    int y = 8;
    boolean isEqual = (x == y);  // false
    boolean isGreater = (x > y);  // false
    boolean notEqual = (x != y);  // true

3.3 Logic Operators

    && (logical AND)
    || (logical OR)
    ! (logical NOT)

Example

    boolean result = (5 > 3) && (2 < 4); // Logical AND

3.4 Assignment Operators

    = (assignment)
    += (addition assignment)
    -= (subtraction assignment)
    *= (multiplication assignment)
    /= (division assignment)
    %= (modulo assignment)

Example

    int x = 5;
    x += 3; // Equivalent to x = x + 3

4 Practice Quiz

4.1 Multiple Choice

What is the correct way to declare a variable of type integer with a value of 100?

a) int x = 100;
b) integer x = 100;
c) x = 100;
d) int x = 100.0;
Which of the following is not a primitive data type in Java?

a) int
b) float
c) String
d) char

What is the output of the following code?

  int a = 10;
  int b = 3;
  System.out.println(a % b);

a) 3
b) 1
c) 0
d) 3.33

Which operator is used for logical AND in Java?

a) &
b) ||
c) &&
d) AND

What is the result of the following expression?

   boolean x = true;
   boolean y = false;
   System.out.println(x || y);

a) true
b) false
c) 1
d) 0

What is the value of the variable x after the following code executes?
```
   int x = 5;
   x += 3;
```
a) 5
b) 3
c) 8
d) 2
Which operator would you use to determine if a number is even

a) /
b) %
c) *
d) +
Given the declaration int num = 10;, which of the following is a valid way to decrement the value of num by 2?

a) num = num - 2;
b) num -= 2;
c) num–; num–;
d) All of the above

4.2 Short Answer

Explain the difference between an integer and a floating-point number in Java.
Write a Java code snippet to declare and initialize variables for a person’s name (String), age (int), and height (double).

4.3 Coding Problem

Write a Java program that:

Given two integers `a` and `b`. (if could, Prompts the user to enter two integers)
Calculates the sum, difference, product, quotient, and remainder of the two numbers.
Prints the results in a formatted output. **Note**: For the coding problem, you would typically be expected to write and compile the code, then provide the output or code itself as your answer.