Taking an element out of an array

[Ron Temple]

I'm trying to take an animal element of an array for filtering but I'm having some problems. I need to take the element i need out of the array. Then I need to find out whether the animal is the type I need. Finally I need to add the animal object to the array. I have to seperate arrays of displayed animals and all the animals but I'm just having trouble figuring out how to do the above. Any advice is greatly appreciated. Here's what I have so far:

   
      
       public void filterDogs()
      {

      
         Iterator i = animals.iterator();
      
         while(i.hasNext()) 
         { 
            Animal a = (Animal)i.next(); 
            if(a instanceof Dog)
              Dog += displayedAnimals.add(a); 
         }
      }

And the entire code:

   import javax.swing.*;  
   import java.util.ArrayList;
   import java.util.*;
   import java.util.Collections;
   import javax.swing.Timer;
   
   
    public class AnimalListDisplay extends JList
   {
      ArrayList<Animal> animals;
      ArrayList<Animal> displayedAnimals;
   	
      boolean specialNeedsOnly = false;
      boolean birdsOn = false;
      boolean dogsOn = false;
      boolean catsOn = false;
   
   
       public AnimalListDisplay(ArrayList<Animal> allAnimals)
      {
        	
         animals = allAnimals;
         displayedAnimals = animals;
      }
       public void addAnimal(Animal animal)
      {
         animals.add(animal);
      	
         setListData(animals.toArray());
      	  
      }
       public void sortAge()
      {
      
         AgeCompare a1 = new AgeCompare();
         Collections.sort(displayedAnimals, a1);
         setListData(displayedAnimals.toArray());
      }
      
   	
       public void sortSize()
      {
      
         Collections.sort(displayedAnimals);
         setListData(displayedAnimals.toArray());
      }
   
   
       public void filterSpecialNeeds()
      {
       
         if(specialNeedsOnly == false)
         {
            displayedAnimals = new ArrayList<Animal>();
         
            Iterator i = animals.iterator();
         
            while(i.hasNext())
            {
               Animal a = (Animal)i.next();
               if(a.getNeeds())
                  displayedAnimals.add(a);
            }
            setListData(displayedAnimals.toArray());
            specialNeedsOnly = true;
         }
         
         else if(specialNeedsOnly == true)
         {
         
            setListData(animals.toArray());
            specialNeedsOnly = false;
         
         }
      }
   
      // public void addAnimal(Animal pet){
        // displayedAnimals.add(pet);
        // animals.add(pet);
      
   
   
      
       public void filterDogs()
      {
  
      
         Iterator i = animals.iterator();
      
         while(i.hasNext()) 
         { 
            Animal a = (Animal)i.next(); 
            if(a instanceof Dog)
               displayedAnimals.add(a); 
         }
      }
       public void filterCats()
      {
         if(catsOn == false)
         {
            displayedAnimals = new ArrayList<Animal>();
         
            Iterator i = animals.iterator();
         
            while(i.hasNext())
            {
               Animal a = (Animal)i.next();
               if(a.getNeeds())
                  displayedAnimals.add(a);
            }
            setListData(displayedAnimals.toArray());
            catsOn = true;
         }
         
         else if(catsOn == true)
         {
         
            setListData(animals.toArray());
            catsOn = false;
         }
      }
       public void filterBirds()
      {
         if(birdsOn == false)
         {
            displayedAnimals = new ArrayList<Animal>();
         
            Iterator i = animals.iterator();
         
            while(i.hasNext())
            {
               Animal a = (Animal)i.next();
               if(a.getNeeds())
                  displayedAnimals.add(a);
            }
            setListData(displayedAnimals.toArray());
            birdsOn = true;
         }
         
         else if(birdsOn == true)
         {
         
            setListData(animals.toArray());
            birdsOn = false;
         
         }
      
      
      }
   }

[David Newton]

I'm lost: what are you trying to do again?

[Allain Walker]

Hi Ron,
try using

for(Animal animal: animals){
if(Dog.class.isInstance(animal)){
displayedAnimals.add(animal);
}
 

You could even pass the class type into a function and reduce the duplication in the code.
I have come up against this sort of issue before and never really had the time to try to figure out why this is happening. I have always just gone with the isInstance() function instead. If somebody can explain it I would be grateful.

[David Newton]

@Allain: you're saying instanceOf doesn't work for you?

@Ron: The fragment, and that fragment embedded in the entire code, are not the same. What *is* happening, and what do you *expect* to happen?

[Allain Walker]

Hi David,
What I am saying is that I have tried to use the instanceof before and I must have made a mistake with it, or not understood how it works. At the time instead of using instanceof I used class.isInstance(o) and achieved the outcome I was looking for.
I didn't have time to examine what I was doing wrong, and it fell of the radar. I now have the time to do that now and will try again.
Thanks
Allain