gistfile1.java

public class Fruit<T extends Fruit.Contents> {
     
     @Setter @Getter
     protected int id;

     @Setter @Getter
     protected Map<String, T> contents;

     @Setter @Getter
     protected String defaultKey;

     protected class Contents {
         @Setter @Getter
         protected String name;
     } 
}


public class Apple extends Fruits<Apple.Contents> {
     protected class Contents extends Fruit.Contents {
         @Setter @Getter
         protected String seed;
     }
}


public class Lemon extends Fruits<Lemon.Contents> {
     protected class Contents extends Fruit.Contents {
         @Setter @Getter
         protected int acidity;
     }
}


Lemon lemon = ...;
lemon.getName(); // shorthand to call lemon.getContents().get(lemon.getDefaultKey).getName(); 
lemon.getAcidity();

Apple apple = ...;
apple.getName();
apple.getSeed();