Sum of elements of any type

Question

public float sum(Object ob) {
    float sum = 0;
    for (int i = 0; i < ob.length; i++) {
        sum += ob[i];
    }

    return sum;
}

How can I implement a function that would return the sum of all the array elements of any type?

Is this homework? Because I'm sure that there's something in the JRE that would handle summing an array for you. — Ignacio Vazquez-Abrams, Mar 19 '11 at 05:57
do you mean a function that takes an array of float arrays, and sums all the elements in all the arrays? — Ptival, Mar 19 '11 at 05:58
What is wrong with the one you already have? What do you want differently? — krock, Mar 19 '11 at 05:59
hey no this function should take any array type. Float, int etc and still be able to return the sum how can i do that ? — user602774, Mar 19 '11 at 06:06
@Ignacio - actually, you'd be wrong. There are no standard methods for summing the elements of arrays ... let alone arrays of different element types. — Stephen C, Mar 19 '11 at 07:02

score 2 · Answer 1 · edited Mar 19 '11 at 07:08

2

An educated guess, I havnt done java in a while. Is a cast in order?

EDIT: Or, change parameter type to float[]:

float[] ob = (float[]) ob;

public float sum(Object ob) {
    float sum = 0;
    float[] ob = (float[]) ob;
    for (int i = 0; i < ob.length; i++) {
        sum += ob[i];
    }
    return sum;

}

edited Mar 19 '11 at 07:08

Mateen Ulhaq

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answered Mar 19 '11 at 06:02

Bodman

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looks close but i get a exception Exception in thread "main" java.lang.ClassCastException: [J cannot be cast to [F – user602774 Mar 19 '11 at 06:09
isnt there way to declare the correct type for variable sum beforehand based on the type of array – user602774 Mar 19 '11 at 06:10
1

Yeah, because the object is not castable to float. Is the object type correct? You sure it isnt an array or arraylist? – Bodman Mar 19 '11 at 06:11
yeah , you can , http://stackoverflow.com/questions/106336/how-do-i-find-out-what-type-each-object-is-in-a-arraylistobject – Bodman Mar 19 '11 at 06:13
well what kind of object is being passed in? is it an array of some sort? – Bodman Mar 19 '11 at 06:22
Try and cast it to an arraylist , its generic – Bodman Mar 19 '11 at 06:24
@Bodman - fail ... won't work ... you can't cast an array to an array list. – Stephen C Mar 19 '11 at 07:30
@Stephen C, No you cant cast it , but isnt that a "asList" method of an Array, Im no Java expert. – Bodman Mar 19 '11 at 18:00
@Bodman - Nope. Arrays.asList works for array types that are assignable to `Object[]` ... and arrays of primitive types are not. – Stephen C Mar 20 '11 at 02:15

score 2 · Answer 2 · answered Mar 19 '11 at 07:28

What you are trying to do is ... basically ... implement a bad design. Arrays of primitives in Java are not type compatible, and you cannot do things on them in a polymorphic fashion.

It is not clear what is the best way to fix your design. But here are a couple of alternatives:

Write a overloaded methods for each of the cases that make sense; e.g.
```
public int sum(int[] ints) ...

public long sum(long[] longs) ...

public float sum(float[] floats) ...
```
Then make sure that you call them on primitive arrays whose type is known at compile time.

Wrap the arrays in classes, and implement the sum method for each of them:

public interface NumberArray {
    double sum();
    ...
}

public class FloatArray {
    private float[] floats;
    public Float(float[] floats) { this.floats = floats; }
    public double sum() {
        double sum = 0.0D;
        for (float f : floats) { sum += f; }
        return sum;
    }
}

and so on.

It is actually possible to implement a float sum(Object array) method ... like this:

public float sum(Object obj) {
    float sum = 0;
    if (obj instanceof float[]) {
        for (float f : (float[]) obj) {
            sum += f;
        }
    } else if (obj instanceof int[]) {
        for (int i : (int[]) obj) {
            sum += i;
        }
    } else if ...
    } else {
        throw new SomeException("Can't sum one of these ...");
    }
    return sum;
}

but that's non-OO and (IMO) really ugly. Better to fix the design.

score 1 · Accepted Answer · answered Mar 19 '11 at 06:18

1

As per the comment on the other answer:

java.lang.ClassCastException: [J cannot be cast to [F

Then it's a long[], not a float[]. Just use long, not float or Object. If you declare it explicitly as method argument, then you don't also need to fiddle with casts.

public long sum(long[] array) {
    long sum = 0;
    for (int i = 0; i < array.length; i++) {
        sum += array[i];
    }
    return sum;
}

Sum of elements of any type

3 Answers3

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