02 - Operators and Expressions

Operators are symbols that perform operations on variables and values. They're the verbs of programming - they make things happen!

Arithmetic Operators

Used for mathematical calculations:

int a = 10;
int b = 5;

int sum = a + b;        // Addition: 15
int difference = a - b; // Subtraction: 5
int product = a * b;    // Multiplication: 50
int quotient = a / b;   // Division: 2
int remainder = a % b;  // Modulus (remainder): 0

Division Note

When dividing integers, Java performs integer division, which means it discards any decimal part. For example, 7 / 2 would result in 3, not 3.5.

int x = 7 / 2;       // 3 (not 3.5!) - Integer division
double y = 7.0 / 2;  // 3.5 - At least one double gives double result
double z = (double) 7 / 2;  // 3.5 - Casting works too

Modulus (%) - The remainder Operator

The modulus operator returns the remainder of a division operation:

int remainder = 10 % 3; // 1 (because 10 divided by 3 is 3 with a remainder of 1)

Compound Assignment Operators

These operators combine an arithmetic operation with assignment:

int a = 10;

a = a + 5;  // The old way

a += 5;     // a = a + 5
a -= 3;     // a = a - 3
a *= 2;     // a = a * 2
a /= 4;     // a = a / 4
a %= 3;     // a = a % 3

Increment and Decrement Operators

Used to increase or decrease a variable's value by 1:

int a = 5;
a++; // Increment: a becomes 6
a--; // Decrement: a becomes 5 again

Prefix vs Postfix

int a = 5;
int b = a++; // b is 5, a is now 6
int c = ++a; // a is 7, c is now 7

Comparison Operators

Used to compare two values, returning a boolean result (true or false):

int a = 10;
int b = 5;

a == b // false - Equal to
a != b // true  - Not equal to
a > b  // true  - Greater than
a < b  // false - Less than
a >= b // true  - Greater than or equal to
a <= b // false - Less than or equal to

Logical Operators

Used to combine multiple boolean expressions:

boolean x = true;
boolean y = false;

x && y // false - Logical AND
x || y // true  - Logical OR
!x     // false - Logical NOT

Combining Logical Operators

boolean result = (a > b) && (b < 10); // true if both conditions are true

String Concatenation

The + operator can also be used to concatenate (join) strings:

String greeting = "Hello, " + "world!"; // "Hello, world!"
String name = "Alice";
String greetingWithName = "Hello, " + name + "!"; // "Hello, Alice!"

Operator Precedence

Operator Precendence means which operator gets evaluated first in an line of code. Think of it like BODMAS/PEMDAS in math!

int result = 10 + 5 * 2; // result is 20, not 30

02 - Operators and Expressions

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