java - How can I change an object if it is in an ArrayList? -

i have arraylist of dogs. if fluffy in arraylist, want change name fido. if not in arraylist, want add it, , change name fido.

so can check if fido exists in arraylist, how can retrieve can make changes? following closest have come. looking along lines of dogs.getelementequalto(new dog("fido"));

import java.util.arraylist;  public class dog {      public static void main(string[] args) {         arraylist<dog> dogs = new arraylist<>();         dogs.add(new dog("fido"));         dog dog = new dog("fido");         if (dogs.contains(dog)) {             dog.name = "fluffy";         }         system.out.println(dogs.get(0).name); //prints fido     }      string name;      public dog(string name) {         this.name = name;     }      @override     public boolean equals(object o) {         if (this == o) return true;         if (!(o instanceof dog)) return false;          dog dog = (dog) o;          return !(name != null ? !name.equals(dog.name) : dog.name != null);     }      @override     public int hashcode() {         return name != null ? name.hashcode() : 0;     } } 

edit:

i tried changing main method this, did not work:

arraylist<dog> dogs = new arraylist<>(); dogs.add(new dog("fido")); dog dog = new dog("fido"); if (dogs.contains(dog)) {     dogs.get(dogs.indexof(dog)).name = "fluffy"; } system.out.println(dogs.get(0).name); 

you can (first) index of fido using:

int indexoffido = dogs.indexof(new dog("fido")); 

and retrieve element using:

dogs.get(indexoffido); 

however, depending upon concrete implementation of list using, may more efficient iterate through list:

dog fido = new dog("fido"); (dog dog : dogs) {   if (fido.equals(dog)) {  // comparison way round, since                            // elements of list can null in general.     // whatever.     break;  // unless want same instances of fido.   } }