Java Comparable to Instance or String

Question

I'm trying to create a class that can either be compared to an instance of the same class, or to String.

For example, consider the following:

public class Record implements Comparable<Record> {
    public String name;

    public Record(String name) {
        this.name = name;
    }

    public int compareTo(Record o) {
        return name.compareTo(o.name);
    }
}

I then place this into an ArrayList as follows:

ArrayList<Record> records = new ArrayList<Record>();
records.add(new Record("3"));
records.add(new Record("1"));
records.add(new Record("2"));

If I then sort them, they are sorted properly:

Collections.sort(records);

However, I not want to be able to get a record via binary search based on a string. For example:

int index = Collections.binarySearch(records, "3");

The problem is that there is no compareTo method that takes a String as argument, and I'm unsure how to implement it.

I tried doing:

public class Record implements Comparable<Record>, Comparable<String> {
    public String name;

    public Record(String name) {
        this.name = name;
    }

    public int compareTo(Record o) {
        return name.compareTo(o.name);
    }

    public int compareTo(String o) {
        return name.compareTo(o);
    }
}

But, of course, you cannot implement the same interface with different arguments more than once.

So, I'm looking for a method to do the above. I have looked at the following previous answers, but have not found one that truly answers this sufficiently. At least, if it did, I did not understand it.

• compareTo and Strings using a Scanner
• Sorting a list of objects based on different data members in Java
• a bunch of others that I don't have the links to now...

Basically, what I want to do is the following:

public int compare(Record r, String s) {
    return r.name.compareTo(s);
}

As far as I can tell, though, you cannot compare objects of differing types without implementing some sort of common interface or superclass. I don't really have that option with String.

Can someone please show me how to do this, if it is possible? Thanks.

UPDATE I realize that I could do the following:

Collections.binarySearch(records, new Record("3"));

But, that is not what I'm after. Thanks.

Answer 1

You can implement Comparable without qualifying it with a type, and check the incoming Object with instanceof, and behave differently depending on what type you receive.