inheritance - How do I implement abstract class inside abstract class in the implementation class in Java? -

i have 2 classes have structures following code.

public class classone {    private data data;    public classone(data data) {     this.data = data;   }    public data getdata() {     return data;   }    public static class data {      //code 1    } } 

---

public class classtwo {    private data data;    public classtwo(data data) {     this.data = data;   }    public data getdata() {     return data;   }    public static class data {      //code 2    } } 

as can see, 2 classes have data object has different implementation. move data object in parent class , implement in 2 classes? might looks following code.

public abstract class abstractclass {    data data;    public abstractclass(data data) {     this.data = data;     }    public data getdata() {     return data;   }    public abstract class data{} } 

---

public class classone extends abstractclass {    public classone(data data) {     super(data);   }    //implementation abstractclass.data   public class data {      //code 1    } } 

---

public class classtwo extends abstractclass {    public classtwo(data data) {     super(data);   }    //implementation abstractclass.data   public class data {      //code 2    }    } 

as know, java extends 1 class, how implement inner abstract class (data)?

this do, if understand problem correctly.

public class abstractclass {      protected abstractdata data;      public abstractclass(abstractdata data) {         this.data=data;     }      public abstractdata getdata() {         return data;     }      public static interface abstractdata {         public int getint();         public boolean getbool();     } }  public class classone extends abstractclass {      public classone(abstractdata data) {         super(data);     }      @override     public abstractdata getdata() {         return data.getbool() ? data : null;     }      public static class dataone implements abstractdata {          @override         public int getint() {             return 0;         }          @override         public boolean getbool() {             return false;         }     } }  public class datatwo implements abstractclass.abstractdata {      @override     public int getint() {         return 42;     }      @override     public boolean getbool() {         return true;     } } 

here can combine abstractclass , classone both dataone , datatwo like.

but don't see why abstractclass should abstract, isn't in exmple. of course, can make abstract , add abstract method like.