Error in using methods in java

Question

I'm still a beginner to using methods in java. I want to print the following series in java using methods.

1 + (1+2)/2! + (1+2+3)/3!.....n terms

I have done this much. I want to know why I'm not able to use s in sum2 method.

public class SERIES {
  int factorial(int n) {
    int res = 1;
    for (int i = 2; i <= n; i++)
      res *= i;
    return res;
  }

  int sum1(int n) {
    int s = 0;
    for (int i = 1; i <= n; i++)
      s += i;
    return s;
  }

  double sum2(int n) {
    double ts = 0.0;
    for (int i = 1; i <= n; i++) {
      ts = s / res;
    }
    return ts;
  }

  void main(int a) {
    int d = sum2(a);
    System.out.println(d);
  }

}

Either call sum1(n) in sum2() or declare s as global variable — Amit Tamrakar
– Amit Tamrakar, Commented Aug 24, 2015 at 15:49
Scope matters. You declared the variable in the method sum1() which is local to that method only. If you want to use across methods, move that to top (instance level). — Suresh Atta
– Suresh Atta, Commented Aug 24, 2015 at 15:49

Jordi Castilla · Accepted Answer · 2015-08-24 15:49:09Z

3

declare s and res as class attributes and them will be accessible from ALL methods of your class, also you must change the main and create a double variable, because sum2() method returns a double.

public class SERIES {
    // s and res are accessible in everywhere in SERIES class.
    int s = 0;
    int res = 1;

    int factorial(int n) {
        for (int i = 2; i <= n; i++)
            res *= i;
        return res;
    }

    int sum1(int n) {
        for (int i = 1; i <= n; i++)
            s += i;
        return s;
    }

    double sum2(int n) {
        double ts = 0.0;
        for (int i = 1; i <= n; i++) {
            ts = s / res;
        }
        return ts;
    }

    void main(int a) {
        double d = sum2(a);   // change to double
        System.out.println(d);
    }

}

answered Aug 24, 2015 at 15:49

Jordi Castilla

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3 Comments

thenewbie Over a year ago

but when I give 'a' as 1, it gives 0.0 whereas it should give 1.

CubeJockey Over a year ago

@thenewbie That's because in this code, s is globally declared as 0. Zero divided by anything will always be zero.

thenewbie Over a year ago

how do i use 's' and 'res' in 'sum2'?

astrohome · Accepted Answer · 2016-10-31 14:26:49Z

2

You should clearly understand the difference between local and global variables.

Basically, what you're declaring inside the { } is a local variable. It is only accessible inside that block. So when in function double sum2(int n) you're trying to access variables s and res they are just not known to that function.

edited Oct 31, 2016 at 14:26

user6613600

answered Aug 24, 2015 at 15:50

astrohome

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Comments

David · Accepted Answer · 2015-08-24 15:49:23Z

Because there is no s in the sum2 method. It's in the sum1 method. And a variable declared within a given scope only exists within that scope.

So either sum2 needs to create such a variable:

double sum2(int n)
{
    double s = 1.0;
    double res = 1.0;

    double ts = 0.0;
    for(int i = 1;i<=n;i++)
    {
        ts = s/res;
    }
    return ts;
}

or it needs to accept that variable as a parameter to the method:

double sum2(int n, double s, double res)
{
    double ts = 0.0;
    for(int i = 1;i<=n;i++)
    {
        ts = s/res;
    }
    return ts;
}

(in which case any code which calls sum2() will need to pass it those values)

Conversely, you can increase the scope. If the entire object should know of s then make it a class-level variable:

public class SERIES {
    double s = 1.0;

    // now any method in this class can access the same instance of s
}

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