Question

I’m failing to create this class hirerarchy that includes a generic that is comparable. What am I missing here? This throws an error.

public class Generics <T extends Comparable<T>> 
    extends Parent<T extends Comparable<T>> {

    ArrayList<T> ar;

    public Generics() {
        ar = new ArrayList<>();
    }

    @Override
    public void add(T elt){
        ar.add(elt);
    }
}

And the parent class is:

public class Parent <T extends Comparable<T>>{
    int size =0;
    public Parent(){
        size=0;
    }

    public void add(T elt){
        size++;
    }
}

Try “Extract Superclass” on the following. I tried extracting the ArrayList and the add(T elt). This is on the following config:

Product Version: NetBeans IDE 7.2 (Build 201207171143)
Java: 1.7.0_07; Java HotSpot(TM) 64-Bit Server VM 23.3-b01
System: Linux version 3.2.0-30-generic running on amd64; UTF-8; en_US (nb)

public class Generics <T extends Comparable<T>> {

    ArrayList<T> ar;
    int size;

    public Generics() {
        ar = new ArrayList<>();
        size = 0;
    }

    public void add(T elt){
        ar.add(elt);
        size++;
    }
}

Answer 1

Try out this

public class Generics <T extends Comparable<T>> 
    extends Parent<T> {

    ArrayList<T> ar;

    public Generics() {
        ar = new ArrayList<>();
    }

    public void add(T elt){
        ar.add(elt);
    }
}