Intro to Java

Variables, Conditions & Loops

Variables

What are variables?

Variables are elements used to store data so we can manipulate and use them in our program.

What are the types of variables?

Unlike JavaScript and Python where the program can just figure it out, we have to be more specific in Java.
Types include: String, int, boolean, double, char

String

This variable is used for text like words or sentences.

How do you declare a String variable?

String greeting = "Hello, world!";

NOTE:
You must use double quotes for strings.
And end every line with a semicolon (;).

Integer (int)

This variable type is used to store whole numbers (no decimals).

How do you declare an int variable?

int age = 16;

Boolean (True / False)

This type of variable is used to store true or false values.

How do you declare a boolean variable?

boolean isStudent = true;

Double

This type of variable is used to store decimal numbers
Examples: 3.14, 9.81, 2.718

How do you declare a double variable?

double pi = 3.14159;

Char (Characters)

This type is used to store a single character.
Characters must be enclosed in single quotes (' ').

How do you declare a char variable?

char grade = 'A';

Conditions (if statements)

What are conditionals?

conditionals are statements that control the flow of a program's execution based on whether a condition is true or false.

if Statement

Basic if structure:

if (condition) {
    // code to run if condition is true
}

Example:

int age = 18;

if (age >= 18) {
    System.out.println("You can vote!");
}

if-else Statement

Structure:

if (condition) {
    // runs if true
} else {
    // runs if false
}

Example:

int score = 45;

if (score >= 50) {
    System.out.println("You passed!");
} else {
    System.out.println("You failed.");
}

if - else if - else Statement

Structure:

if (condition1) {
    // runs if condition1 is true
} else if (condition2) {
    // runs if condition2 is true
} else {
    // runs if neither is true
}

Example:

int grade = 85;

if (grade >= 90) {
    System.out.println("A");
} else if (grade >= 80) {
    System.out.println("B");
} else {
    System.out.println("C or lower");
}

Relational Operators

Loops

What are loops?

Loops are used to repeat a block of code multiple times until a condition is met.

Types:

• for loop
• while loop

for Loop

Structure:

for (initialization; condition; update) {
    // code to repeat
}

Example:

for (int i = 0; i < 5; i++) {
    System.out.println("i is: " + i); // Output is: 0 1 2 3 4
}

while Loop

Structure:

while (condition) {
    // code to repeat
}

Example:

int i = 0;
while (i < 5) {
    System.out.println("i is: " + i);
    i++;
}

Loop Use Case Example

Print even numbers from 2 to 10 using a loop:

for (int i = 2; i <= 10; i += 2) {
    System.out.println(i);
}