Compiler throws "unexpected type" error

Question

Hi,
I am newbie to Generics, I wrote the below program as part of my learning exercise:
=================
class One<T> implements Comparable<? extends One<T>>
     T var;
     public void setVal(T val){
          var=val;
     public T getVal(){
          return this.var;
     public int compareTo(One<T> o1){
          if(this.getVal().equals(o1.getVal())){
return 0;
}else {
return 1;
class Two<T> extends One<T>
     public int compareTo(Two o1){
          // do nothing
          return 0;
class GenTest
     public static void main(String[] args)
          One<String> obj_01=new One<String>();
          obj_01.setVal("Vinayaka");
          One<String> obj_02=new One<String>();
          obj_02.setVal("Vinayaka");
=========
Compilation fails with the below error:
javac GenTest.java
GenTest.java:1: unexpected type
found : ? extends One<T>
required: class or interface without bounds
class One<T> implements Comparable<? extends One<T>>
^
1 error
Can any one please explain me what is wrong with this program ?

Answer 1

You are mixing syntaxes. Your definition should be:
class One<T> implements Comparable<One>(PS: please use code tags when posting code)