Using compareTo in Java to Sort

Question

Basically i'm attempting to write a compareTo that does the comparison based on the value of compareByWord . If compareByWord is true, I want it to compare based on the word, but if it's false, I want it to compare based on count .

class WordCount implements Comparable //Error saying WordCount must implement the inherited abstract method Comparable.compareto (Object)
{
String word;
int count;
static boolean compareByWord;
public WordCount(String aWord)
{
    setWord(aWord);
    count = 1;
}
private void setWord(String theWord)
{
    word=theWord;
}
public void increment()
{
    count+=1;
}
public static void sortByWord()
{
    compareByWord = true;
}
public static void sortByCount()
{
    compareByWord = false;
}
public String toString()
{
    String result = String.format("%s (%d)",word, count);
    return result;
}
public String getWord()
{
    return word;
}
public int getCount()
{
    return count;
}
@Override
public int compareTo(WordCount other) {  //Error saying compareTo (WordCount) of type WordCount must override or implement a supertype method.
    if (compareByWord == true)
    {
        return word.compareTo(other.getWord());
    }
    if (compareByWord == false)
    {
        return count.compareTo(other.getCount()); //Error saying it cannot invoke compareTo int on primitive type int.
    }
    return 0;
}
}

My class was perfect before I tried to implement this, not sure where I'm going wrong here. Any and all help is much appreciated.

Answer 1

Change the declaration to

class WordCount implements Comparable<WordCount> { // generic version

The method signature in Comparable<WordCount> is compareTo(WordCount obj) while for the raw version it's compareTo(Object obj) .

With the usage of @Override , the compiler makes sure that you actually override the parent method. And the problem is that compareTo(WordCount obj) does not override compareTo(Object obj) .

Answer 2

Use Integer count not int count . Integer is an object which implements Comparable whereas int is a primitive as the error message describes. For javadocs:

public final class Integer
extends Number
implements Comparable<Integer>

Make sure you change your accessor methods to use Integer as well of course.

That will take care of your final error.

Answer 3

must implement the inherited abstract method Comparable.compareto (Object)

So pass Object, not WordCount. Now you're trying to overload this function, not override .