Return type

exercise No. 230

Q:

We consider a method computing a circle's area:

static public float getArea (int radius) {
  return radius * radius * 3.1415926;
}

  1. Compilation fails due to the following error:

    Required type: float
Provided: double

    Explain the error message.

    Tip

    Dissect the underlying expression.

  2. You are not allowed to change the method's signature. What is the cleanest way to correct the programming error?

A:

  1. The expression radius * radius * 3.1415926 is being evaluated from left to right. The literal 3.1415926 is of type double. We thus have: 

    int * int * double
  \   /      /
   int * double
     \    /
     double

  2. Replacing the double literal by a float literal leaves us with an overall float expression resolving the issue: 

    radius * radius * 3.1415926F

   int * int * float
     \   /     /
      int * float
        \   /
        float
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