java - Acceptable use of instanceof -

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• is acceptable use of instanceof? 2 answers

i'm new java , struggling design problem. know use of instanceof may indicate design flaw , understand given animal/dog/cat classes example, replacing bark() , meow() makenoise() etc.

my question is, sensible design if need call methods not have corresponding method depending on type of subclass? example, if want call new method biteleash() if class dog nothing @ if it's cat?

i did consider having biteleash() in animal nothing, , overriding in dog, there methods many seems clunky solution. in similar vein, if caller needs different depending on subclass has hold of, eg. terminate if subclass cat? instanceof acceptable here, or there better way?

public class animal {      string name;      public animal(string name) {         this.name = name;     }      public string getname() {         return name;     }      public void makenoise() {         system.out.println("some noise generic animal!");     }  }  public class cat extends animal {      public cat(string name) {         super(name);     }      @override     public void makenoise() {         system.out.println("meow");     } }  public class dog extends animal {      public dog(string name) {         super(name);     }      @override     public void makenoise() {         system.out.println("woof");     }      public void biteleash() {         system.out.println("leash snapped!");     } }  import java.util.random;  public class codeexample {       public static void main(string[] args) {          animal animal = getsomeanimal();         system.out.println("my pet called " + animal.getname());         animal.makenoise();          if (animal instanceof dog) {             dog dog = (dog) animal;             dog.biteleash();             // lots of other things because animal dog             // eg. sign puppy training lessons         }     }      private static animal getsomeanimal() {         animal animal;         random randomgenerator = new random();         int randomint = randomgenerator.nextint(100);               if (randomint < 50) {             animal = new dog("rover");         }         else {             animal = new cat("tiddles");         }         return animal;     } } 

composition here, , idiomatic in java.

design interface called, say, leashable. implemented dog, not cat.

rather using instanceof, can attempt reference cast leashable see if it's implemented particular object.

in opinion, should continue in similar vein: build noisyanimal interface too. perhaps noisy why should noisiness pertinent animals? implementing parrot, say, have technical challenges beyond cat or dog. maintainable programs isolate areas of complexity , composition helps achieve that.