Thread: Taking an element out of an array

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;   }     } }

Originally Posted by Bryan

public abstract class Animals {	public static final Integer CATS = 0;	public static final Integer DOGS = 1;	public static final Integer BIRDS = 2;	protected Hashtable<Animal> animals = new Hashtable<Animal>(); //protected!!!  	public abstract Hashtable<Animal> collect(int specieType);	public abstract void add(Animal a);	public abstract Animal get(int id);	public abstract void edit(Animal a);	public abstract boolean remove(Animal a); }   public class AnimalCollection extends Animals {	private Hashtable<Animal> collection = new Hashtable<Animal>();  	public Hashtable<Animal> collect(int specieType)	{	String specie;	switch(specieType)	{	case 0:	specie = "Cat";	break;	case 1:	specie = "Dog";	break;	case 2:	specie = "Bird";	break;	default:	throw new Exception("Unknown type.");	}  	Hashtable<Animal> col = new hashtable<Animal>();	for(Animal a : super.animals)	{	if(a instanceof specie)	{	col.put(a.hashCode(), a);	}	}	this.collection = col; //if you want to have the same collection some time later, you load this and dont call the method again(performance)	return col;	}  	@override	public void add(Animal a) {}  	@override	public Animal get(int id) {}  	@override	public void edit(Animal a) {}  	@override	public boolean remove(Animal a) {} }   Call: AnimalCollection aC = new AnimalCollection(); Hashtable dogsCollection = aC.collect(Animals.DOGS);

I made this with notepad++ so there may be some syntax errors.

Hmm, that needs a bit more work...
Don't forget that a Hashtable is a keyed collection, so should be declared with two generic type arguments - but a Hashtable won't work here if you want more than one instance of each species in the collection - Hashtable keys are unique.
You could profitably replace the Integer 'specieType' with an enum.
It would simplify things if an Animal knew its specieType - which it should.
Should AnimalCollection really extend Animals, or does this complicate things?
There seems little point in having a Hashtable of a single animal species, ArrayList would be more appropriate (especially if an Animal knows its Species)?

If all that's needed is to extract a particular species from a mixed collection, wouldn't something like this be simpler:

import java.util.ArrayList; import java.util.List;   class AnimalFilter { public static void main(String[] args) { List<Animal> animals = new ArrayList<Animal>(); animals.add(new Dog(..)); animals.add(new Cat(..)); animals.add(new Bird(..)); animals.add(new Dog(..)); animals.add(new Bird(..));   AnimalFilter filter = new AnimalFilter(); List<Animal> dogsCollection = filter.collect(animals, Animal.Species.DOGS); ... // do something with Dogs }  	public List<Animal> collect(List<Animal> animals, Animal.Species species)	{	List<Animal> selectedAnimals = new ArrayList<Animal>();	for(Animal animal : animals)	{	if(animal.isSpecies(species)) {	selectedAnimals.add(animal);	}	}	return selectedAnimals;	} }   abstract class Animal { public enum Species { CATS, DOGS, BIRDS }   protected Species species;   public Species getSpecies() { return species; } public boolean isSpecies(Species s) { return species == s; } }   class Dog extends Animal { ... } class Cat extends Animal { ... } class Bird extends Animal { ... }

If an explicit Species type id isn't needed, you could even get rid of the Species enum and just use the Animal class type:

class AnimalFilter { public static void main(String[] args) { List<Animal> animals = new ArrayList<Animal>(); animals.add(new Dog(..)); animals.add(new Cat(..)); animals.add(new Bird(..)); animals.add(new Dog(..)); animals.add(new Bird(..));   AnimalFilter filter = new AnimalFilter(); List<Animal> dogsCollection = filter.collect(animals, Dog.class); ... // do something with Dogs }  	public List<Animal> collect(List<Animal> animals, Class speciesClass)	{	List<Animal> selectedAnimals = new ArrayList<Animal>();	for(Animal animal : animals)	{	if(animal.getClass().equals(speciesClass)) {	selectedAnimals.add(animal);	}	}	return selectedAnimals;	} }   abstract class Animal { ... } class Dog extends Animal { ... } class Cat extends Animal { ... } class Bird extends Animal { ... }

YMMV.