Running method on object problem

[Jack Fletcher]

Hi everyone,

I've got a problem with my code, which consists of 2 classes.

The error I'm being given at compile is <identifier> expected at the line:

37. poly1.evaluate();

Here is the rest of the code for classes Polynominal and Test:

// Import ArrayList
import java.util.*;
import java.lang.Math;
public class Polynominal
{

    // variable assignments
    
    public int x = 0;
    public int sum = 0;
    
    
    // Create a new empty ArrayList called 'coefficient'
    public ArrayList<Integer> coefficient = new ArrayList<Integer>();
    
        
    /**
     * Constructor for objects of class Polynominals
     */
    Polynominal(ArrayList<Integer> coefficient)
    {
        this.coefficient = coefficient;
    }
    
    // Method: evaluate using X placeholder
    
    public int evaluate () {
        
        int sum = 0;
        
        for (int v: coefficient)
        {
            int get = coefficient.get(v); // get the coefficient
            int eval = get*(int)Math.pow(x,v); // evaluate each block
            sum += eval; // add up running total of block addition
        }
        return sum;
    }   
    
        // Method: toString
    
    public String toString() {
        String output = "";
        
        
        for (int i=0; i <coefficient.size(); i++) //TODO: change to <size
        {
            output = output + " " + this.coefficient.get(i);
        }
        
        return output;
        
    }
}


import java.util.*;
public class Test
{
   public static void main(String[] args) { 
       
    // Create 2 ArrayLists
    ArrayList<Integer> array = new ArrayList<Integer>();
    ArrayList<Integer> array2 = new ArrayList<Integer>();
    
    // Add elements to 'array'
    array.add(7);
    array.add(0);
    array.add(0);
    array.add(1);
    array.add(3); // 70013
    
    // Add elements to 'array2'
    array2.add(8);
    array2.add(1);
    array2.add(0);
    array2.add(0);
    array2.add(2); // 81002
       
    // Create 2 Polynominal objects, taking the arraylists as parameters
    Polynominal poly1 = new Polynominal(array);
    Polynominal poly2 = new Polynominal(array2);
       
    // Display elements in array object
    // Uses toString class to print contents of the object
    System.out.println(poly1);
    System.out.println(poly2);
    
    
   }
   
   // Evaluate polynominal 1 using evaluate() in Polynominal class
   poly1.evaluate();
   
   // Evaluate polynominal 2 using evaluate() in Polynominal class
   poly2.evaluate();
}

Hope somebody can help me with this one!
Thanks a lot.

[Jeff Verdegan]

Hi, and welcome to the Ranch!

For future reference, when posting code, please UseCodeTags(⇐click) so it will be readable. I've added them to your original post for you.

As for your problem, you can't call a method out in the middle of nowhere in a class definition. That has to be as part of another method body (such as in main()), or in a constructor or initializer block or a combination variable declaration/initialization statement.

[Jack Fletcher]

Great! That error is gone but now there's another one! Any idea what's happened here?

int get = coefficient.get(v);

Gives the error:
java.lang.IndexOutOfBoundsException:
Index: 7, Size: 5 (in java.util.ArrayList)

When the Test class is run.
Thanks.

[Jeff Verdegan]

Jack Fletcher wrote:

int get = coefficient.get(v);

Gives the error:
java.lang.IndexOutOfBoundsException:
Index: 7, Size: 5 (in java.util.ArrayList)

Everything you need to know is right there. You're trying to get the 8th element (at index 7) of a List that has only 5 elements (at indices 0..4). So either you don't have as many things in the list as you thought you did, or you're trying to get a different element than you thought you were trying to get.

[Jack Fletcher]

Jeff Verdegan wrote:

Jack Fletcher wrote:

int get = coefficient.get(v);

Gives the error:
java.lang.IndexOutOfBoundsException:
Index: 7, Size: 5 (in java.util.ArrayList)

Everything you need to know is right there. You're trying to get the 8th element (at index 7) of a List that has only 5 elements (at indices 0..4). So either you don't have as many things in the list as you thought you did, or you're trying to get a different element than you thought you were trying to get.

I see. So the 'int v' variable is the index position which I want the for loop to use in iterating through the coefficient object. I don't understand why it's iterating further than the size (5) of the arrayList?

[Jeff Verdegan]

Jack Fletcher wrote:

I see. So the 'int v' variable is the index position which I want the for loop to use in iterating through the coefficient object. I don't understand why it's iterating further than the size (5) of the arrayList?

Nobody said anything about iterating. If you read the docs for get(), you'll see that get(N) gets the Nth element from the List. In the case of an ArrayList, it does that by direct, indexed access into an array. In the case of a LinkedList, it iterates linearly. In the case of a skip list, it iterates using an approach that should be faster than a simple linear count. But we don't need to know or care about any of that. That's just an implementation detail. All we care about is that get(7) gets the 8th element.

As for why it's getting something larger than the 5th element, it's because you're telling it to. If you can't see where your code is doing that, you should add some print statements that show you what's going on at each step, so you can see where and how v is becoming 7. For instance:

        for (int v: coefficient)  
        {  
            System.out.println("in for loop, v is " + v);          // <-- ADD THIS LINE
            int get = coefficient.get(v); // get the coefficient  

With any luck, that will make your logic error blindingly obvious, and you'll smack your forehead and go, "DUH!" If not, post again.