Methods — Java Cheat Sheets

1 DECLARING & CALLING METHODS

public static int square(int number) { return number * number; } // calling it: int result = square(5); // 25

Anatomy of a method

Modifiers — public static
Return type — int, or void if nothing returned
Method name — square
Parameter list — (int number)
Method body — the code block, with a return if non-void

2 CASE STUDY: RANDOM NUMBERS & enums

Random randomNumbers = new Random(); int face = 1 + randomNumbers.nextInt(6); // 1–6 enum Status { WON, LOST, CONTINUE } Status game = Status.CONTINUE;

Key points

Random.nextInt(n) gives 0 to n-1 → shift with +1 for dice-style ranges
enum defines a fixed, named set of constants — safer than raw ints for "modes" or "states"
Great for simulations: dice games, card games, state machines

3 SCOPE OF DECLARATIONS

Local scope

A variable declared inside a method (or block) exists only within that block.

Field / class scope

Instance variables declared in a class are visible to all of that class's methods.

Shadowing

A local variable with the same name as a field hides the field inside that method.

4 METHOD OVERLOADING

int add(int a, int b){ return a+b; } double add(double a, double b){ return a+b; } int add(int a, int b, int c){ return a+b+c; }

Rule

Multiple methods can share the same name as long as their parameter lists differ (number or types of params). The compiler picks the right one to call based on the arguments given — this is called the method's signature.

5 CLASS Math & JAVA API PACKAGES

Math method	Purpose
`Math.sqrt(x)`	square root
`Math.pow(x,y)`	x raised to power y
`Math.abs(x)`	absolute value
`Math.max/min(a,b)`	larger/smaller value

Packages

Related classes are grouped into packages (e.g. java.util, java.math)
Import a class with import java.util.Random;
Math's methods are static — call them via the class name, no object needed

6 METHOD-CALL STACK & ACTIVATION RECORDS

main() — waiting

calculate() — waiting

square() — running now

How it works

Each method call pushes a new activation record (stack frame) with its local variables/parameters
When a method returns, its frame is popped off — control returns to the caller
Last-In-First-Out (LIFO) order — just like Java's Stack class
Too many nested calls (e.g. infinite recursion) → StackOverflowError

7 ARGUMENT PROMOTION & CASTING

Implicit promotion

A smaller/less-precise type widens automatically to match a parameter — e.g. passing an int where a method expects a double.

Explicit casting

double avg = 7.8; int whole = (int) avg; // 7 — narrowing needs a cast

8 OBJECTS-NATURAL CASE STUDY: JAVA DATE/TIME API

LocalDate today = LocalDate.now(); LocalDate meeting = LocalDate.of(2026, 9, 20); long daysLeft = ChronoUnit.DAYS.between(today, meeting);

Key classes (java.time)

LocalDate — a calendar date, no time/timezone
LocalTime / LocalDateTime — time-of-day / both combined
Period / Duration — amounts of time
Replaces the old, error-prone Date/Calendar classes

9 METHOD REFERENCE TABLE — class Math (FULL)

Method	Purpose
`Math.abs(x)`	absolute value
`Math.ceil(x)`	rounds up to nearest whole
`Math.floor(x)`	rounds down to nearest whole
`Math.round(x)`	rounds to nearest whole
`Math.max(a,b)/min(a,b)`	larger/smaller value
`Math.pow(x,y)`	x raised to power y
`Math.sqrt(x)`	square root
`Math.random()`	double in range [0.0, 1.0)

Random Class Method	Purpose
`nextInt()`	random int, full range
`nextInt(n)`	random int from 0 to n-1
`nextDouble()`	random double [0.0, 1.0)
`nextBoolean()`	random true/false

JAVA — CHAPTER 5