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Resizing an array in Java

(Implementing ArrayList) ArrayList is implemented in the Java API. Implement ArrayList and the methods defined in table below (Hint use an array to store the elements in ArrayList. If the size of ArrayList exceepds the capacity of the current array, create a new array that doubles the size of the current array and copy the contents of the current to the new array)

+ArrayList() creates an empty list

+add(o: Object):void appends a new element o at the end of this list

+add(index: int, o: Object): void Adds a new element o at the specified index in this list

+clear():void removes all the elements form this list

+contains(o:Object):boolean returns true if this list contains element o

+get(index:int):Object returns the element from this list at the specified index

+indexOf(o:Object):int returns the index of the last matching element in this list

+isEmpty():boolean returns true if this list contains no elements

+lastIndexOf(o:Object):int returns the index of the last matching element in this list

+remove(o:Object):boolean removes the element o from this list

+size():int returns the number of elements in this list

+remove(index:int):boolean removes the element at the specified index

+set(index:int, o:Object):Object sets the elements at the specified index

This is the question that I was given: I'm getting an error when I debug the program. I have to have a main to run it? Where am I suppose to put the main. Also, if there is anything wrong in my code could you please help fix the issue. Thanks

import java.util.AbstractList;
import java.util.List;
import java.util.RandomAccess;
 
 
public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable
     {
       // The capacity of the ArrayList is the length of this array buffer.
        
          private transient Object[] elementData;
	private int modCount;
      
          public ArrayList(int initialCapacity) 
          {
            super();
            if(initialCapacity < 0)
            throw new IllegalArgumentException("Illegal Capacity: "+initialCapacity);
             this.elementData = new Object[initialCapacity];
          }
 
  
     // Constructs an empty list with an initial capacity of 100.
 
        public ArrayList()
          {
            this(100);
          }
        public boolean isEmpty()
           {
              return size() == 0;
          }
 
       public boolean contains(Object o)
        {
          return indexOf(o) >= 0;
        }
 
     public int indexOf(Object o)
      {
         if (o == null)
           {
              for (int i = 0; i < size(); i++)
              if (elementData[i]==null)
               return i;
           }
           else
            {
               for (int i = 0; i < size(); i++)
               if (o.equals(elementData[i]))
               return i;
       }
        return -1;
  }
 
     public int lastIndexOf(Object o)
      {
         if (o == null)
          {
            for (int i = size()-1; i >= 0; i--)
            if (elementData[i]==null)
            return i;
           }
          else
          {
            for (int i = size()-1; i >= 0; i--)
            if (o.equals(elementData[i]))
            return i;
          }
         return -1;
       }
 
       public E remove(int index)
        {
           rangeCheck(index);
           int modCount++;
           E oldValue = elementData(index);
           int numMoved = size() - index - 1;
           if (numMoved > 0)
           System.arraycopy(elementData, index+1, elementData, index,numMoved);
           elementData[--size()] = null;
           return oldValue;
         }
 
    private E elementData(int index) 
    {
		// TODO Auto-generated method stub
		return null;
	}
 
 
	private void rangeCheck(int index) 
	{
		// TODO Auto-generated method stub
		
	}
 
 
	public boolean remove(Object o)
     {
      if (o == null)
       {
         for (int index = 0; index < size(); index++)
         if (elementData[index] == null)
          {
             fastRemove(index);
             return true;
          }
        }
        else
         {
           for (int index = 0; index < size(); index++)
           if (o.equals(elementData[index]))
            {
              fastRemove(index);
              return true;
            }
         }
          return false;
   }
 
  private void fastRemove(int index)
   {
        modCount++;
        int numMoved = size() - index - 1;
        if (numMoved > 0)
       System.arraycopy(elementData, index+1, elementData, index,
       numMoved);
       elementData[--size()] = null;
    }
 
     public void clear()
      {
        modCount++;
        for (int i = 0; i < size(); i++)
        elementData[i] = null;
        size() = 0;
      } 
 
        public int size()
           {
             checkForComodification();
             return this.size();
           }
 
 
		private void checkForComodification() {
			// TODO Auto-generated method stub
			
		}
 
 
	
		public E get(int index) {
			// TODO Auto-generated method stub
			return null;
		}
 
 }

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CEHJ

>> I have to have a main to run it?

You do. You can put it inside the class for testing only, but it's better to create a separate class

laughsalot

ASKER

I know I have to implement with a test program, is the code I have so far good to go? I'm working on the test program now. I will post when I am done.

CEHJ

You need to ensure the correct instance variables. This fixes it so it compiles:

import java.util.AbstractList;
import java.util.List;
import java.util.RandomAccess;
 
 
public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable
     {
       // The capacity of the ArrayList is the length of this array buffer.
        
          private transient Object[] elementData;
        private int modCount;
      
          public ArrayList(int initialCapacity) 
          {
            super();
            if(initialCapacity < 0)
            throw new IllegalArgumentException("Illegal Capacity: "+initialCapacity);
             this.elementData = new Object[initialCapacity];
          }
 
  
     // Constructs an empty list with an initial capacity of 100.
 
        public ArrayList()
          {
            this(100);
          }
        public boolean isEmpty()
           {
              return size() == 0;
          }
 
       public boolean contains(Object o)
        {
          return indexOf(o) >= 0;
        }
 
     public int indexOf(Object o)
      {
         if (o == null)
           {
              for (int i = 0; i < size(); i++)
              if (elementData[i]==null)
               return i;
           }
           else
            {
               for (int i = 0; i < size(); i++)
               if (o.equals(elementData[i]))
               return i;
       }
        return -1;
  }
 
     public int lastIndexOf(Object o)
      {
         if (o == null)
          {
            for (int i = size()-1; i >= 0; i--)
            if (elementData[i]==null)
            return i;
           }
          else
          {
            for (int i = size()-1; i >= 0; i--)
            if (o.equals(elementData[i]))
            return i;
          }
         return -1;
       }
 
       public E remove(int index)
        {
           rangeCheck(index);
           int modCount++;
           E oldValue = elementData(index);
           int numMoved = size() - index - 1;
           if (numMoved > 0)
           System.arraycopy(elementData, index+1, elementData, index,numMoved);
           elementData[--size()] = null;
           return oldValue;
         }
 
    private E elementData(int index) 
    {
                // TODO Auto-generated method stub
                return null;
        }
 
 
        private void rangeCheck(int index) 
        {
                // TODO Auto-generated method stub
                
        }
 
 
        public boolean remove(Object o)
     {
      if (o == null)
       {
         for (int index = 0; index < size(); index++)
         if (elementData[index] == null)
          {
             fastRemove(index);
             return true;
          }
        }
        else
         {
           for (int index = 0; index < size(); index++)
           if (o.equals(elementData[index]))
            {
              fastRemove(index);
              return true;
            }
         }
          return false;
   }
 
  private void fastRemove(int index)
   {
        modCount++;
        int numMoved = size() - index - 1;
        if (numMoved > 0)
       System.arraycopy(elementData, index+1, elementData, index,
       numMoved);
       elementData[--size()] = null;
    }
 
     public void clear()
      {
        modCount++;
        for (int i = 0; i < size(); i++)
        elementData[i] = null;
        size() = 0;
      } 
 
        public int size()
           {
             checkForComodification();
             return this.size();
           }
 
 
                private void checkForComodification() {
                        // TODO Auto-generated method stub
                        
                }
 
 
        
                public E get(int index) {
                        // TODO Auto-generated method stub
                        return null;
                }
 
 }

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SOLUTION