java - Search specific objects in ArrayList by attribute -

good day,

imagine have following code: (these not attributes)

class owner {     private string name; }  class car {     private owner owner;     private string brandname;      public boolean isclean() { // not included in contructor         return false;     }  class fuelcar extends car {     private string fueltype;      public boolean isclean() {         if (fueltype.equals("diesel")){             return false;         } else {             return true;     } }  class electriccar extends car {     private int batterylevel;      public boolean isclean() {         return true;     } } 

the objects added arraylist:

arraylist<car> cars = new arraylist<>(); 

examples:

cars.add(new auto("audi", new owner("peter"))); cars.add(new auto("fiat", new owner("rob"))); cars.add(new auto(mercedes, null)); cars.add(new electriccar(10, "opel ", new owner("unknown"))); cars.add(new electriccar(100,"google", new owner("google"))); cars.add(new fuelcar("diesel", "seat", new owner("tom"))); cars.add(new fuelcar("gasonline", "smart", new owner("marcel"))); 

now questions are:

1. how can make method list cars have value isclean "true";

2. how can make method following signature: public static void printcarsspecific(arraylist cars, string fueltype) example if put in: printcarsspecific("gasoline"); cars shown when printing arraylist.

ps: it's not homework. education typed code above myself , didnt copy , paste because become way large.

i tried these methods:

public static void printbedrijfsautosmettype(arraylist<auto> autos, string brandstof) {     iterator<auto> iter = autos.iterator();     while (iter.hasnext()) {         auto auto = iter.next();          if (auto instanceof brandstofauto) {             string brandstof1 = ((brandstofauto) auto).getbrandstof();             if (!brandstof1.equals(brandstof) || brandstof1 == null) {                 iter.remove();             }         }         (int = 0; < autos.size(); i++) {             system.out.println(autos.get(i));         }      } } 

and

   public static void printschoneautos(arraylist<auto> autos) {         iterator<auto> iter = autos.iterator();         while (iter.hasnext()) {             auto auto = iter.next();             if (auto instanceof brandstofauto) {                 boolean isschoon = ((brandstofauto) auto).isschoon();                 boolean isschoon3 = auto.isschoon();                 if (isschoon3 == false || isschoon == false) {                     iter.remove();                 }             }             (int = 0; < autos.size(); i++) {                 system.out.println(autos.get(i));             }         }     } 

i guess don't have delete these items i've seen examples under here.

if using java 8 use fancy streams such :

list<car> cleancars = carlist.stream().filter(car -> car.isclean()).collect(collectors.tolist());  list<car> carsfilteredonfueltype = carlist.stream().filter(car -> fueltype.equals(car.fueltype)).collect(collectors.tolist));