How do I convert these methods from Arrays to ArrayLists?

[David Vach]

Hi all, so I have to convert my ArrayBasics class into an ArrayListBasics class. Basically, I have to change everything from and Array to ArrayList. However, I have begun to get a little bit lost. I though I was understanding how to convert all of these arrays into array lists, but I have begun to get errors when checking to make sure that my code compiles. Right now, I am getting an error in my reverse method that says  unexpected type, found variable, require value. If someone could help me work though some of the issues I am havng in converting my code, that would be great, because as of right now, I am honestly lost.  Here is my original Array code:

public class ArrayBasics 
{
    /*** <<< CODE COMPLETE >>>
    * prints out an array of any size 
    ***/
    public static void print(int[] a) 
    {
        for (int i = 0; i < a.length; i++)
        {
            if (i < a.length-1)
            {
                System.out.print(a[i] + ", ");
            }
            else if (i == a.length-1)
            {
                System.out.print(a[i]);
            }
        }
        System.out.print("\n");
    }

   /***     <<< CODE COMPLETE >>>
    * returns the largest integer in an array 
    ***/
    public static int max(int[] a) 
    {
        int maxValue = 0;
        for (int i = 0; i < a.length; i++)
        {
            if (a[i] > maxValue)
            {
                maxValue = a[i];
            }
        }
        return maxValue;
    }

   /***      <<< CODE COMPLETE >>>
    * returns the smallest integer in an array
    ***/
    public static int min(int[] a) 
    {
        int minValue = a[0];
        for (int i = 0; i < a.length; i++)
        {
            if (a[i] < minValue)
            {
                minValue = a[i];
            }
        }
        return minValue;
    }

    /***      <<< CODE COMPLETE >>>
    * returns boolean true if the array is in sorted order
    * else returns false
    ***/
    public static boolean inOrder(int[] a) 
    {
        boolean inOrder = true;
        for (int i = 0; i < a.length - 1; i++) 
        {
            if (a[i] > a[i+1]) 
            {
                inOrder = false;
            }
        }
        return inOrder;
    } 
    
    
   /***        <<< CODE COMPLETE >>>
    * reverses the order of the elemets in the array 
    ***/
    public static void reverse(int[] a)
    {
        for (int i = 0; i < a.length/2; i++)
        {
            int reverseOrder = a[i];
            a[i] = a[a.length - 1 - i];
            a[a.length - 1 - i] = reverseOrder;
        }
    }

   /***        <<< CODE COMPLETE >>>
    * merges two sorted arrays into 1 new array, maintains the sorted order 
    ***/
    public static int[] merge(int[] a, int[] b) 
    {
        int[] merge = new int[a.length + b.length];
        int i = 0, j = 0, k = 0;
    
        while (i < a.length && j < b.length)
        {
            if (a[i] < b[j])
            {
                merge[k++] = a[i++];
            }
    
            else        
            {
                merge[k++] = b[j++];
            }
        }
    
        while (i < a.length)
        {
            merge[k++] = a[i++];
        }
    
    
        while (j < b.length)  
        {
            merge[k++] = b[j++];
        }
    
        return merge;
    }

   /*** 
    * The main method is complete.
    */  
   public static void main(String[] args) { 
        System.out.println("\n---array example 1---");
        int num1[] = {4,5,9,7,3,4,8};
        print(num1);
        System.out.println("The largest value is: " + max(num1));
        System.out.println("The smallest value is: " + min(num1));
        System.out.println("In order: " + inOrder(num1));
        
        System.out.println("\n---array example 2---");
        int num2[] = {24,87,96,102,874,941};
        print(num2);
        System.out.print("reverse order: ");
        reverse(num2);
        print(num2);
        System.out.println("In order: " + inOrder(num2));
        
        System.out.println("\n---array example 3---");
        int num3[] = {2,6,8,9};
        int num4[] = {1,3,7,9,10};
        print(num3);
        print(num4);
        System.out.print("merged array: ");
        int merged[] = merge(num3,num4);
        print(merged);
        System.out.println("In order: " + inOrder(num3));

   }
}

and here is the code I have been working on converting. I believe some of the methods work, but I am at a loss for the merge method and what I am doing wrong in the reverse method. When I had cancelled out these methods to check to see if anything else was wrong, I also found that my min method was giving an out of bounds exception error. Im sorry, I am very confused. Here is my ArrayList code I am working on:

import java.util.ArrayList;
 
 public class ArrayListBasics 
 {
   /*** <<< CODE COMPLETE >>>
   * prints out an array of any size 
   ***/
   public static void print(ArrayList <Integer> a) 
   {
       for (int e : a)
       {
           if (e < a.size()-1)
           {
               System.out.print(e + ", ");
           }
           else if (e == a.size()-1)
           {
               System.out.print(e);
           }
       }
       System.out.print("\n");
    }

   /***     <<< CODE COMPLETE >>>
    * returns the largest integer in an array 
    ***/
    public static int max(ArrayList <Integer> a) 
    {
        int maxValue = 0;
        for (int e : a)
        {
            if (e > maxValue)
            {
                maxValue = e;
            }
        }
        return maxValue;
    }

   /***      <<< CODE COMPLETE >>>
    * returns the smallest integer in an array
    ***/
    public static int min(ArrayList <Integer> a) 
    {
        int minValue = a.get(0);
        for (int e : a)
        {
            if (a.get(e) < minValue)
            {
                minValue = a.get(e);
            }
        }
        return minValue;
    } 

   /***      <<< CODE COMPLETE >>>
   * returns boolean true if the array is in sorted order
   * else returns false
   ***/
   public static boolean inOrder(ArrayList <Integer> a) 
   {
       boolean inOrder = true;
       for (int i = 0; i < a.size() - 1; i++) 
       {
           if (a.get(i) > a.get(i)) 
           {
               inOrder = false;
           }
       }
       return inOrder;
   } 
       
   /***        <<< CODE COMPLETE >>>
   * reverses the order of the elemets in the array 
   ***/
   public static void reverse(ArrayList <Integer> a)
   {
       for (int i = 0; i < a.size()/2; i++)
       {
           int reverseOrder = a.get(i);
           a.get(i) = a.get(a.size() - 1 - i);
           a.get(a.size() - 1 - i) = reverseOrder;
       }
   } 
  
   /***        <<< CODE COMPLETE >>>
   * merges two sorted arrays into 1 new array, maintains the sorted order 
   ***/
   public static ArrayList <Integer> merge (ArrayList <Integer> a, ArrayList <Integer> b) 
   {
       ArrayList <Integer> merge = new ArrayList <Integer> (a.length + b.length);
       int i = 0, j = 0, k = 0;
   
       while (i < a.size() && j < b.size())
       {
            if (a.get(i) < b.get(j))
            {
                merge[k++] = a[i++];
            }
    
            else        
            {
                merge[k++] = b[j++];
            }
       }
    
       while (i < a.length)
       {
           merge[k++] = a[i++];
       }
        
       while (j < b.length)  
       {
           merge[k++] = b[j++];
       }
    
       return merge;
   }
    
 
   /*** 
    * The main method is complete.
    */  
   public static void main(String[] args) { 
        System.out.println("\n---array example 1---");
        ArrayList<Integer> num1 = new ArrayList<Integer>();
        num1.add(4);
        num1.add(5);
        num1.add(9);
        num1.add(7);
        num1.add(3);
        num1.add(4);
        num1.add(8);
        print(num1);
        System.out.println("The largest value is: " + max(num1));
        System.out.println("The smallest value is: " + min(num1));
        System.out.println("In order: " + inOrder(num1));
        
        System.out.println("\n---array example 2---");
        ArrayList<Integer> num2 = new ArrayList<Integer>();
        num2.add(24);
        num2.add(87);
        num2.add(96);
        num2.add(102);
        num2.add(874);
        num2.add(941);
        print(num2);
        System.out.print("reverse order: ");
        reverse(num2);
        print(num2);
        System.out.println("In order: " + inOrder(num2));
        
        System.out.println("\n---array example 3---");
        ArrayList<Integer> num3 = new ArrayList<Integer>();
        num3.add(2);
        num3.add(6);
        num3.add(8);
        num3.add(9);
        ArrayList<Integer> num4 = new ArrayList<Integer>();
        num4.add(1);
        num4.add(3);
        num4.add(7);
        num4.add(9);
        num4.add(10);
        print(num3);
        print(num4);
        System.out.print("merged array: ");
        int merged[] = merge(num3,num4);
        print(merged);
        System.out.println("In order: " + inOrder(num3));

   }
}

[Paul Clapham]

Your min() method should be almost identical to max(), except for > versus <, shouldn't it?

[David Vach]

Paul Clapham wrote:Your min() method should be almost identical to max(), except for > versus <, shouldn't it?

Yeah, thanks for that. That helped me get my min method correct. However, after compiling without the reverse and merge methods, which I'm still not sure how to get to work, I found that my print method is only printing some of my numbers in the array. It does not print all of them. I am also not sure why my inOrder method does not work, because it is only returning true when it should be returning false false true.

[David Vach]

I have gotten my boolean to work for my order I believe as well as finding the min value. However, I am still having trouble finding out how to fix my reverse order and merge.

[David Vach]

I'm also not sure how to get rid of the last comma, which I was able to do on my ArrayBasics class.

[David Vach]

Topic has moved here: https://coderanch.com/t/673204/java/transfer-methods-Array-ArrayList#3150005