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Resizing an array in Java

Posted on 2009-04-30
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Last Modified: 2012-08-14
(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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Question by:laughsalot
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7 Comments
 
LVL 86

Expert Comment

by:CEHJ
ID: 24272930
>> 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
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Author Comment

by:laughsalot
ID: 24273022
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.
0
 
LVL 86

Expert Comment

by:CEHJ
ID: 24273140
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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LVL 92

Assisted Solution

by:objects
objects earned 20 total points
ID: 24274600
you can put the main in any class you want, I'd suggest creating a separate test class and put your test main in there

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LVL 92

Expert Comment

by:objects
ID: 24274611
for resizing an array see the following:
http://helpdesk.objects.com.au/java/how-do-i-resize-a-java-array

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Accepted Solution

by:
laughsalot earned 0 total points
ID: 24274731
thanks guys I got it up and running
0
 
LVL 86

Expert Comment

by:CEHJ
ID: 24352426
laughsalot, i'm curious as to why you accepted an answer that's essentially the same as my earlier one..?
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