AP Computer Science A — Topic 1.10: Calling Class Methods

In Java, some methods belong to the class instead of an object. These methods are called class methods, also known as static methods.

Example you already know:

System.out.println("Hello");

println() is being called using the class name System.out.

How to Identify Class Methods

Class methods contain the word static in the method header:

public static int abs(int x)

How to Call Class Methods

We call a class method using:

ClassName.methodName()

Examples:

Math.sqrt(25);          // returns 5.0
Math.random();          // returns a random double 0.0-1.0
Integer.parseInt("42"); // returns 42

Notice: We do NOT create an object of Math.

Why the AP Exam Cares

Students must NOT do this:

Math m = new Math();
double r = m.random();   // WRONG - NOT ALLOWED

The correct call:

double r = Math.random();

Summary Table