Parts of a method header

A parameter is a variable in the header that receives a value. An argument is the value you pass when you call the method. The signature is the method name plus the ordered list of parameter types; the return type is not part of it.

public static double average(int a, int b)
//            ^return   ^name    ^parameters
// signature: average(int, int)

Calling a method

Arguments must match the parameters in number, order, and type. Java uses call by value: each parameter gets a copy of its argument. When a method is called, the caller pauses, the method runs, and then control returns to just after the call.

A void method returns nothing, so you call it as a statement. A non-void method returns a value that you should store, print, or use in an expression.

static int area(int w, int h) { return w * h; }
static void greet(String name) { System.out.println("Hi, " + name); }

System.out.println(area(3, 4));
int a = area(2, 5);
greet("Sam");
System.out.println(a);

12
Hi, Sam
10

Overloading

Overloaded methods share a name but have different signatures. Java picks the one whose parameter types match the arguments.

static int max(int a, int b) {
  if (a > b) return a;
  return b;
}
static double max(double a, double b) {
  if (a > b) return a;
  return b;
}
static int max(int a, int b, int c) {
  return max(max(a, b), c);
}

System.out.println(max(3, 9));
System.out.println(max(2.5, 1.0));
System.out.println(max(4, 1, 7));

9
2.5
7