Thread: General question on using array inside a nested for loop

Hello everyone,
For the past couple of weeks, I have been working on a final project for my Java Introduction course. I pretty much have it completed, but since I have a couple of weeks before it is due, I wanted to try and improve upon it and possible get some extra credits. Before I change any code in the program, I thought I would start a basic program to to see if I could get the basic principal to work. To start, here is the code I have been practicing with.

import java.util.ArrayList;
import java.util.Random;
 
public class AnimalArrays {
    int index;
    int sheep = 2;
 
    String xPos;
    String yPos;
    String positions;
    ArrayList<Integer> list = new ArrayList<Integer>(5);
    String[] sheepCreate = new String[sheep];
 
    public static void main(String[] args) {
        AnimalArrays newAnimal = new AnimalArrays();
    }
 
    public AnimalArrays() {
        // creates a list from 1 to 5
        for(int i = 1; i <= 5; i++) {
            list.add(i);
        }
        Random rand = new Random();
        for(int count = 0; count < sheep; count++) {
            // creates a String[] with x and y positions for each sheep
            index = rand.nextInt(list.size());
            xPos = Integer.toString(list.remove(index));
            index = rand.nextInt(list.size());
            yPos = Integer.toString(list.remove(index));
            positions = xPos + "," + yPos;
            sheepCreate[count] = positions;
            System.out.println(positions);
        }
        // removes unused items from the list
        for(int count = 0; count < list.size(); count++) {
            list.remove(count);
        }
 
        startingGrid();
    }
 
    public void startingGrid(){
        // writes the numbers 1-5 along the top
        for (int xValue = 1; xValue < 6; xValue++) {
            System.out.print("  " + xValue);
            } // end of for statement
                 System.out.println("");
 
            // writes the numbers 1-5 down the left side
            for (int yValue = 1; yValue < 6; yValue++) {
                System.out.print(yValue + " ");
 
                for (int xValue = 1; xValue < 6; xValue++) {
 
                    //for (int sc = 0; sc < 2; sc++) {
 
                        if (xValue == (Integer.parseInt(String.valueOf(sheepCreate[0].charAt(0)))) && yValue == Integer.parseInt(String.valueOf(sheepCreate[0].charAt(2)))) {
                            System.out.print("S  ");
                        } // end of if statement
                        else
                            System.out.print("*  ");
 
                    //} // end of inner for statement
 
                }// end of middle for statement
 
                System.out.println("");
            } // end of outer for statement
 
    } // end of startingGrid method
}

You sill see inside the startingGrid method, I have 3 for loops nested together (1 is commented out). As it sits, it prints the grid perfectly with the one sheep("S") in its correct position, however if I uncomment the last for loop, and change the 0 in the sheepCreate[0] to sc to get both sheep to show up, this is were it messes everything up.

I have been banging my head the entire day trying to understand why. Can anyone give me an explanation on where I went wrong.

My thought process for the above code is;
first for loop sets Y to 1
Second for loop sets X to 1
third for loop would goes through the the sheep array (2 in total) and compares the 2 values stored to the x and y value, if true, it puts an 'S' there other wise it puts a '*' there.

as the third loop is done, second loop increases by 1 until it is done then first loop increases by 1 till its done (hopefully that made sense)
The final product is to have a grid with multiple sheep shown on it.

Any help you can give will help greatly.

Thanks

This forum will not allow me to upload any images (click on the manage attachments button and nothing opens to allow an upload) so I will do my best to describe what is going on.

As currently programmed the output looks like this;
5,2 <- first set of coordinates taken from the for loop in the AnimalArrays method (this one prints out perfectly the way the code is now)
3,4 <- second set of coordinates taken from the for loop in the AnimalArrays method
...1 2 3 4 5
1 * * * * *
2 * * * * S <- location matches the first set of coordinates
3 * * * * *
4 * * * * *
5 * * * * *

as soon as I uncomment the last nested for loop in the startingGrid method and convert the 0's in the "sheepCreate[0].charAt(0)" to "sc" (the variable in the last FOR loop, sheepCreate[sc].charAt(0)) and rerun it this is what appears;
2,5
4,1
...1 2 3 4 5
1 * * * * * * * * * *
2 * * * * * * * * * *
3 * * * * * * * * * *
4 * * * * * * * * * *
5 * * S S * * * * * *

You can see that both the 'S' are not in the correct location and also a second grid was drawn right beside it

what I am trying to make appear is this;
2,5
4,1
...1 2 3 4 5
1 * * * S *
2 * * * * *
3 * * * * *
4 * * * * *
5 * S * * *

As for the "Where does the code use an index to look at the contents of the sheepCreate array at different indexes?" question, directly in the IF statement,
if (xValue == (Integer.parseInt(String.valueOf(sheepCreate[0].charAt(0)))) && yValue == Integer.parseInt(String.valueOf(sheepCreate[0].charAt(2))))

I take the first value and convert it to an INTEGER and compare it to the xValue variable created in the middle FOR loop. Same goes for the second value, but compares it to the yValue.
I hope this is what you were asking.

In the second example shown, I change the [0] value to [sc] (the last FOR loops control value). This way that value will change every rotation. Currently I have that loop stop at 2 but once I can get this figured out, I will change that to a TotalSheep value, this way if there is 5 sheep, it will stop on 5 or stop on 4 if there are only 4 sheep, and so on.

As for your last statement, I am not sure I understand correctly. Creating a String[] for each sheep is the only way I can see a variable holding 2 positions, so I convert them to an INT so I am able to compare them to the xValue and yValue locations. If I don't convert them, I get an error "trying to compare a String to an Int." If this is the wrong way of thinking, then I am open to learning the correct way.

Is there a new version of the code that does that?

its in the code given, I just commented out the for loop that controls it and manually changed the [sc] to [0]

The logic for the code could be:
nested loops that look at each row and the columns in that row
If there is a sheep at that row,column print "S"
else print "*"

this is what I have been attempting to do with the nested for loops.

I'm starting to think the way Java (OOP) is written is messed up, seems like to have to write more code than what seems to be necessary. Maybe once I advance more into the course it might start to make sense, but right now it seems that Java wants you to jump around from method to method, class to class to get to the results. A lot of movement when you should be able to use 1 or 2 to get the job done. Then again it could be that I just don't understand all of it yet.

Anyways, back to your suggestion about creating a sheep class, if I create the sheep class and put the String [] sheepCreate in there, I would still have to convert them to an INT so that they can be used as comparison values, so when the nested for loop run, looking at each individual spot on the grid and comparing them to each sheep, would the outcome not be the same as now.

There would not be any Strings. The x and y values would be stored in the Sheep object as int values, no Strings.

You will find as programs get larger, that separating the logic into various methods will simplify the code and make it easier to read and understand.
Nesting for loops three deep makes the code more complicated and delicate and makes changes to it harder.

Thanks Norm,
I will play around with your suggestions and see what I come up with.

Hi Norm,
Took your advice, and started over, here is the code so far. (no grid on this one, will wait to apply it)

import java.util.ArrayList;
import java.util.Random;
 
public class AnimalArrays {
    int index;
    int sheep = 2;
 
    ArrayList<Integer> list = new ArrayList<Integer>(5);
    String[] sheepCreate = new String[sheep];
 
    public static void main(String[] args) {
        AnimalArrays newAnimal = new AnimalArrays();
    }
 
    public AnimalArrays() {
 
        sheepCreate sheep1 = new sheepCreate();
        sheepCreate sheep2 = new sheepCreate();
 
        // creates a list
        for (int count = 1; count <= 5; count++) {
            list.add(count);
            //sheepNames.add("sheep" + (Integer.toString(count)));
        }
 
        Random rand = new Random();
 
            index = rand.nextInt(list.size());
            sheep1.xValue = list.remove(index);
            index = rand.nextInt(list.size());
            sheep2.xValue = list.remove(index);
            index = rand.nextInt(list.size());
            sheep1.yValue = list.remove(index);
            index = rand.nextInt(list.size());
            sheep2.yValue = list.remove(index);
 
 
        System.out.println(sheep1.xValue + "," + sheep1.yValue);
        System.out.println(sheep2.xValue + "," + sheep2.yValue);
    }
}
 
class sheepCreate{
    int xValue;
    int yValue;
 
}

This works and assigns the x and y values to the sheep class. Only problem is in this example there are only 2 sheep, so I played around with the following to see if you can create objects of sheepCreate using a loop this way, if the sheep number increases so does sheep objects.

import java.util.ArrayList;
import java.util.Random;
 
public class AnotherAnimalArray {
    int index;
    int sheep = 2;
 
    ArrayList<Integer> list = new ArrayList<Integer>(5);    // creates an ArrayList of numbers , 5 numbers max
    ArrayList<String> sheepNames = new ArrayList<String>();             // creates an ArrayList of sheepNames
 
    public static void main(String[] args) {
        AnotherAnimalArray newAnimal = new AnotherAnimalArray();        // creates a new instance of AnotherAnimalArray
    }
 
    public AnotherAnimalArray() {
 
        // creates a list
        for (int count = 1; count <= 5; count++) {
            list.add(count);                                            // adds the numbers 1-5 to the list ArrayList
            sheepNames.add("sheep" + (Integer.toString(count)));        // adds the names of the sheep1 to Sheep5 to the sheepNames ArrayList
        }
 
        /*
        Is it possible to use the sheepNames values in a loop to create new objects of sheepCreate
        */
 
 
        Random rand = new Random();
        index = rand.nextInt(list.size());                              // sets index to a random location in the list ArrayList
 
    }
}
 
class sheepCreate{
    int xValue;
    int yValue;
 
}

as you can probably see, I did not have any luck. So my question now is, "is it possible to create objects using a loop", if not, I think I will just decide on a total number of sheep available and hard code each one in just like in the first example above.