Question

I am trying to wrap my mind around something in java. When I pass an object to another class’ method, can I not just call any methods inherent to that object class?

What is the reason code such as the example below does not compile?

Thank you,

class a {   public static void myMethod(Object myObj) {     myObj.testing();   } }   class b {   public void testing() {     System.out.println ('TESTING!!!');   } }   class c {     public static void main (String[] args) {     b myB = new b();         a.myMethod(myB);     } } 

Edit: The reason I have left the parameter in myMethod as type Object, is because I would like to be able to pass in a variety of object types, each having a testing() method.

Answer 1

If you would like to pass in a variety of objects with testing() methods, have each object implement a Testable interface:

public interface Testable {    public void testing() } 

Then have myMethod() take a Testable.

public static void myMethod(Testable testable) {   testable.testing(); } 

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Edit: To clarify, implementing an interface means that the class is guaranteed to have the method, but the method can do whatever it wants. So I could have two classes whose testing() methods do different things.

public class AClass implements Testable {    public void testing()    {       System.out.println('Hello world');    } }  public class BClass implements Testable {    public void testing()    {       System.out.println('Hello underworld');    } }