[java] Abstract methods in Java

The error message tells the exact reason: "abstract methods cannot have a body".

They can only be defined in abstract classes and interfaces (interface methods are implicitly abstract!) and the idea is, that the subclass implements the method.

Example:

 public abstract class AbstractGreeter {
   public abstract String getHelloMessage();

   public void sayHello() {
     System.out.println(getHelloMessage());
   }
 }

 public class FrenchGreeter extends AbstractGreeter{

   // we must implement the abstract method
   @Override
   public String getHelloMessage() {
     return "bonjour";
   }
 }

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