对数组元素的奇数索引求和

Question

I have this program, which does a whole heap of stuff but the part i'm having trouble with is summing the odd indexes in an arraylist.

Every 1, 3, 5, 7, etc. I need to sum and add to a variable. The variable is of datatype BigFraction and the ArrayList - knowledge takes BigFractions only .

So originally I had

 //Returns the combined probability (the odd indexes of the arraylist)
public BigFraction weight() {
    BigFraction sum;
    if (knowledge.indexOf(knowledge)%2 == 1)
        sum+ = no idea what to put in here
        return sum;
    }
}

I'm really not sure if this is the right syntax for getting indexes of an Arraylist either... I guess you could use a .add or something too, but if anyone could shed light that would be awesome.

Cheers,

Sim

Answer 1

Try this out :

// Returns the combined probability (the odd indexes of the arraylist)
public BigFraction weight() {
    BigFraction sum;
    for (int index = 1; index < knowledge.size(); index = index + 2) {
        sum = sum.add(knowledge.get(index));
    }

    System.out.println("Sum is  " + sum);

    return sum;
}

Answer 2

Here is a hint: you already know what the odd indices are. You've listed them in your question. All you have to do is find a way to loop over them.

Once you've figured that out, you'll need to find a way to get the element at the given index.

The rest, I am sure, will be easy.