Methods, Parameters & Returns

A method is a named, reusable unit of behavior: it takes inputs (parameters), does work, and may hand back a result (return value).

static double withTax(double price) {
    return price * 1.1;
}

Read the signature: static (belongs to the class itself — the word behind why main can run without creating an object), double (the type it returns), withTax (the name), double price (one parameter, typed).

Calling it: double total = withTax(19.99); — the value 19.99 is the argument, copied into the parameter. Two rules the compiler enforces:

• The returned value's type must match the declared return type (or be convertible).
• A method that declares a return type must return on every path through its body. void methods return nothing and may skip return (or use a bare return; to exit early).

static String verdict(int score) {
    if (score >= 60) {
        return "pass";
    }
    return "fail";     // needed! the if-path alone would not cover all cases
}

Parameters are copies — primitive arguments are copied by value, so changing a parameter inside a method never changes the caller's variable:

static void bump(int n) { n = n + 1; }

int x = 5;
bump(x);
System.out.println(x);   // still 5

(Objects are references-copied-by-value — the method can modify the object it was given but not re-point the caller's variable. Module 7 returns to this; for now, primitives-are-copies is the whole story.)

Next: the static word, demystified.