Unit 1 Cycle 2 Day 19: Spotting the Error: Math Methods
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Spotting the Error: Math Methods
Section 1.13 — The Math Class
Key Concept
Error-spotting with Math class methods tests your knowledge of return types and valid arguments. Math.pow(2, 3) returns 8.0 (a double), not 8. Math.sqrt(-1) returns NaN, not an error. Math.abs(Integer.MIN_VALUE) overflows and returns a negative number. Math.random() takes no arguments. The AP exam creates code where a Math method return value is assigned to an incompatible type or used in a context that assumes the wrong type.
A student writes the following code. Which line contains an error?
Which line will cause a compile-time error?
Answer: (A) Line 1
The Math class has a private constructor, so you cannot create Math objects.
Line 1: new Math() causes a compile error. All Math methods are static, so you call them on the class itself (e.g., Math.sqrt()), not on an object.
Lines 2-4: All valid. Math.sqrt(25) returns 5.0. Math.abs(-10) returns 10. Math.random() returns a value in [0.0, 1.0).
Why Not the Others?
(B) Math.sqrt(25) returns double and is stored in a double. Perfectly valid.
(C) Math.abs(-10) with an int argument returns int. Stored in an int. Valid.
(D) Math.random() returns double and is stored in a double. Valid.
Common Mistake
The Math class is a utility class with only static methods. You never need (and cannot) create a Math object. Always call methods as Math.methodName().
AP Exam Tip
If a class has only static methods, you call them using the class name, not an object. Math.random(), not m.random(). The AP exam tests whether you know when to use new and when to call static methods directly.