在 Java 中将对象强制转换为其超类

Question

Learning Java here and I try to cast on a super class and i cant access to subclass methods, is it possible, I am doing something wrong.

I have this:

public class Musician {
      
  public String name;
  public String surname;
}

public class Instrumentist extends Musician{
  
  public String getInstrumento() {
    return instrumento;
  }
  
  public void setInstrumento(String instrumento) {
    this.instrumento = instrumento;
  }
  
  private String instrumento;
  public Instrumentist(String nombre, String name, String surname){
    this.name = nombre;
    this.surname = surname;
  } 
}

public class Main {
  public static void main(String[] args) {
    Musician m = new Instrumentist("Antonio", "Vivaldi", "none");
  
    System.out.println(m);
  }
}

I know I can do Instrumentist i = new Instrumentist("Antonio", "Vivaldi", "none") but then what is the purpose of Cast to superclass?

Answer 1

The concept is like this:
The superclass/interface provides general implementation or a contract. The subclass overrides/implements that contract.
To make sure that you can assign different implementations of that contract at runtime, you use reference of a Superclass and assign object of a subclass to it.
Musician m = new Instrumentist("Antonio", "Vivaldi", "none");
Here, with m , you can call methods defined in Musician class, but if your subclass has any other methods apart from those defined superclass, you can not access them using m .
If subclass overrides any method, then even after using reference of superclass, say m , java would make sure that at runtime , overridden method in subclass is called.