Topic 1.10 — Calling Class Methods

Goal: recognize and write calls to class methods (also called static methods), match calls to method signatures, and store/ use returned values correctly.

The big idea

A class method belongs to the class itself, not to a specific object. You call it using the class name, a dot, and the method name.

Pattern: ClassName.methodName(arguments)

Class method vs. instance method

Class method: called with a class name (e.g., Math.random()).
Instance method: called with an object/variable (you’ll do this in Topic 1.14).

General syntax

// call a class method
ClassName.methodName(arg1, arg2, ...);

// store a returned value
returnType var = ClassName.methodName(...);

Match the call to the signature

When you call a method, you must match the method’s signature (name + parameter types/order).

// Example signature:
double pow(double a, double b)

// Valid call:
double result = Math.pow(2.0, 3.0);

Return values: use or ignore

If a method returns a value, you can:

store it in a variable
use it directly in an expression

double r = Math.random();          // store
int n = (int) (Math.random() * 10); // use in expression

`void` methods can’t be assigned

If a method’s return type is void, it returns nothing—so you cannot store it in a variable.

// Suppose this signature:
void doSomething()

// This is NOT allowed:
int x = doSomething();

Common class methods you’ll see

These are examples of “call with the class name” methods (details of Math come next in 1.11):

Math.random()
Math.abs(...)
Math.pow(...)

The key for 1.10 is the calling pattern, not memorizing everything.

Tracing with class methods

Treat the method call as producing a value, then follow the rest of the code.

double r = Math.random();
int x = (int) (r * 5);

If you’re asked to trace, the question will usually give you enough to reason about the result.

Exam mindset

Class methods are called with ClassName. not an object variable.
Arguments must match the signature (count, types, order).
Return type tells you what can store the result.
If it’s void, don’t try to assign it.

Quick self-check

What is the general pattern for calling a class method?
What does the return type tell you?
Why can’t you assign the result of a void method?
What must match a method signature when calling it?
Rewrite a class method call in a sentence (English).

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