Calling Class Methods

Math.abs is a class method, sometimes called a static method. It's written once inside the Math class and marked static, which means no Math object needs to exist for it to run. You call it with the class name instead of an object name: Math.abs(-9), not some Math object's abs(-9). Contrast this with instance methods, which belong to a specific object and need one built with new before you can call them.

When you call Math.abs(-9), the program jumps into the method's code, substitutes -9 for whatever parameter name the method header uses, runs the method body, and then returns a value back to the exact spot where the call was written. That returned value replaces the call itself, as if you had typed the value there by hand. Arguments line up with parameters strictly by position and type: the first argument fills the first parameter slot, the second fills the second, and so on.

This lets you build expressions out of nested calls, evaluated inside out. Math.max(Math.abs(-9), 4) first runs Math.abs(-9), which becomes 9, then runs Math.max(9, 4), which becomes 9. That final 9 sits where the whole expression was, ready to be stored, printed, or used in more math. If you just write Math.√x; on its own line and never store or print it, the computed value still gets returned, but nothing captures it, so it's thrown away instantly. The method call connects directly to the next topic, writing expressions and assignment, since every returned value needs somewhere to go to actually matter.