CODEWITHSUNDEEP
javasearchcollections
Noor
Noor

Reputation: 20130

Search through Java collection using class attribute

I have an abstract class like this:

public abstract class Ingredient {
    protected int id;
}

and a list

List <Ingredient> ingredientList = new ArrayList <Ingredient>()

I want to be able to get an Ingredient from the ingredientList using id.

I did something like this:

public abstract class Ingredient implements Comparable<Ingredient>{
        protected int id;
        @Override
    public int compareTo(Ingredient o) {
        // TODO Auto-generated method stub
        if (this.id > o.id){
            return 1;
        }
        return 0;
    }
    }

but still not working

Upvotes: 1

Views: 301

Answers (7)

Craig P. Motlin
Craig P. Motlin

Reputation: 26740

If you use Eclipse Collections you can use the detect method.

final int idToFind = ...;
ListIterable<Ingredient> ingredientList = FastList.newListWith(...);
Ingredient ingredient = ingredientList.detect(new Predicate<Ingredient>()
{
    public boolean accept(Ingredient eachIngredient)
    {
        return eachIngredient.getId() == idToFind;
    }
});

If you cant change the type of ingredientList, you can still use the static utility form of detect.

Ingredient ingredient = ListIterate.detect(ingredientList, new Predicate<Ingredient>()
{
    public boolean accept(Ingredient eachIngredient)
    {
        return eachIngredient.getId() == idToFind;
    }
});

When Java 8 is released lambdas, you will be able to shorten the code to:

Ingredient ingredient = ingredientList.detect(eachIngredient -> eachIngredient.getId() == idToFind);

Note: I am a committer for Eclipse collections.

Upvotes: 1

isvforall
isvforall

Reputation: 8926

public Ingredient getIngredientById(int id) {
   for (Ingredient ingredient : ingredientList) {
      if (ingredient.id == id) {
         return ingredient;
      }
   }
}

Upvotes: 0

Stefan Rasmusson
Stefan Rasmusson

Reputation: 5595

for (Ingredient ingredient : IngredientList) {
  if (ingredient.getId() == id) {
    System.out.println("found");
  }
}
System.out.println("not found");

Upvotes: 2

AlexWien
AlexWien

Reputation: 28727

When you use List.contains() to find the Ingredient with id, then override equals() and hashCode() { return id};

In equals(): in equal compare this.id with other.id .

Upvotes: 0

Sebastian
Sebastian

Reputation: 431

Just a guess, but could it be that this is what you mean:

Best way to use contains in an ArrayList in Java?

contains() method of list uses equals() and hashCode()

Upvotes: 0

Reimeus
Reimeus

Reputation: 159754

If you need to perform regular lookups, a Map is probably a better collection to use here:

Map<Integer, Ingredient> ingredientMap = new HashMap<>();

Upvotes: 2

cybye
cybye

Reputation: 1171

you can do (within you class)

interface Callback { public void handle(Indredient found); }

public void search(List<Ingredient> ingredientList, int id, Callback callback) { 
  for(Ingredient i : ingredientList) if(i.id == id) callback.handle(i)
}

and then 

ingredients.search ( 10, new Callback() { 
       public void handle(Ingredient found) {
            System.out.println(found);
       }
   });

or something similar...

ps.: i answered before you changed you question ;)

Upvotes: 0

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