Hello,

I'm having a problem with a Java program that needs to implement the Comparable<E> interface. Its basically for a HuffmanNode class to construct elements of a Huffman Tree. My nodes need to be comparable to integer values (ie, the frequency of the characters in each node), but I'm having some problems writing the class header to start my problem.

A couple examples:
When my class header reads as

I get an error that says

So I tried changing the type of comparable to another HuffmanNode. My logic was if I can compare two nodes, it should be easy enough to cast an int to a HuffmanNode. This brought about the header

Which brought about pretty much the same error as before:

Same idea again:
Header:

produced the error

I then tried to make it generic:

produced:

After this, I decided to try and change the header a bit more, so I changed implements to extends and that only produced a no interface expected error. That wasn't really a surprise, I knew it would work with an interface, but thought it was worth a try.

Anyway, to my question finally. How can I get my HuffmanNode class to implement the Comparable<E> interface? I'm using the Dr Java IDE, with Java 6, using Windows Vista.

Ah, never mind. I've finally figured out what I was doing wrong. My method signature for the compareTo method was wrong.

Hello,

I'm having the same problem but i don't understand what you mean by : My method signature for the compareTo method was wrong. I've look at my method compareTo and i can't find an error...well i'm not a pro so can you please help me with any indication?

thx.

A signature of a method consists of its name and its arguments types but ignoring its return type.
For example, the method compareTo in the Comparable interface is written as:

public int compareTo(Object o);

(Remember that, because it is defined in an interface, the method is implicitly abstract) but its signature is just:

compareTo(Object)

If you have a class called ClassX that is supposed to implement the Comparable interface but instead of making a method in this class with the above signature you make a method with a different signature, such as one that is like the above method but has a different type of argument or has no arguments such as one with the signature:

compareTo( )

Then this will not override but overload the abstract method inherited from the Comparable interface and you will get an error message like:

ClassX is not abstract and does not override abstract method compareTo(java.lang.Object) in java.lang.Comparable

 Also remember that java is case sensitive so that the signatures: CompareTo(Object) and compareto(Object) are not the same signatures as: compareTo(Object)

I hope this helps. AndrewH:)

The main purpose of Comparable interface is compare to Objects
the signature is look like this
c:/> javap java.lang.Comparable
public interface Comparable {
        public abstract int compareTo(java.lang.Object);
}
Note: if u implement the Comparable interace u need not to decrease the previlige
      i.e if Comparable interface the function always in public mode
      public int compareTo(Object);

for example u try to compare two Integer references the code look like this
public int compareTo(Integer i) {
       if(this.i > i)
             return 1;
        return 0;
}
the compareTo return only 0, 1 and -1




K.Mallikarjunarao