How to accept an empty integer value?

Question

My program calculates the surface area of a cone (pi * radius * slant-height). I'm using an if-elseif ladder which says that if the slant-height is left empty and the vertical-height is entered, the program will calculate the slant-height via Pythagoras theorem. But I don't know how to make the program accept a null value

I tried using if(slant_height==null) but it says that the types are incompatible and == is a "bad operator type"

{
public void CSAcone(double radius,double slant_height,double height) {
    if (slant_height == null)
    {
         slant_height=Math.sqrt((radius*radius) + (height*height));
         double CSA=(22*radius*slant_height) / 7;

         System.out.println("radius= "+radius);
         System.out .println("height= "+slant_height);
         System.out .println("Curved Suface Area= "+CSA);
    }

    if(height == null) 
    {
        double CSA=(22*radius*slant_height) / 7;

        System.out.println("radius= " + radius);
        System.out.println("height= " + slant_height);
        System.out.println("Curved Suface Area= " + CSA);
    }
}}

As the method signature is written, `slant_height` will never be null, because you cannot call `CSAcone` by providing a `null` value for that variable, the code wouldn't compile. Notice `slant_height` is `double`, not `Double`. — lealceldeiro, May 18 '19 at 08:44
Read this, https://stackoverflow.com/questions/8643276/object-vs-primitive — Burak Akyıldız, May 18 '19 at 08:54

score 1 · Answer 1 · answered May 18 '19 at 08:55

try this :

 public void CSAcone(double radius, double slant_height, double height) {
    if (slant_height == 0.0f) {
        slant_height = Math.sqrt((radius * radius) + (height * height));
        double CSA = (22 * radius * slant_height) / 7;
        System.out.println("radius= " + radius);
        System.out.println("height= " + slant_height);
        System.out.println("Curved Suface Area= " + CSA);
    }
    if (height == 0.0f) {
        double CSA = (22 * radius * slant_height) / 7;
        System.out.println("radius= " + radius);
        System.out.println("height= " + slant_height);
        System.out.println("Curved Suface Area= " + CSA);
    }
}

I could have done that but it would mean that the user has to enter 0.0 in one of the boxes — Screwdriver, May 19 '19 at 12:36

coder21 · Answer 2 · 2019-05-18T09:05:51.750

null can be cast to any reference type, but not to any primitive type such as int or boolean.

You can use primitive types and send a special value to specify emptyness.

Or just use object types (Integer, Boolean, Double etc.) and check null values(as you did).

public void CSAcone(Double radius,Double slant_height,Double height){
   if(radius == null){}
   if(slant_height == null){}
   if(height == null){}
   // ...
}

score 0 · Accepted Answer · answered May 18 '19 at 08:59

0

Change your variable types to the wrapper classes(Integer, Double) of primitive types(int, double). In Java, primitive types cannot be null.

answered May 18 '19 at 08:59

thuva4

1,185
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How to accept an empty integer value?

3 Answers3