Question

I’m getting the following error with some Java code I’ve written:

internal error; cannot instantiate () at <anonymous <any>> to ()

What I’ve done is created an interface similar to java.lang.Comparable, which is defined as follows:

public interface Comparable<T>
{
    public int compareTo(T o);
}

My interface is:

public interface CustomComparable<T>
{
    public int compare(T a, T b);
}

If I try to create an anonymous inner class using Comparable, it’s fine…

public void someThing()
{
    Comparable<Object> o = new Comparable<Object>()
    {
        public int compareTo(Object o)
        {
            // ...
        }
    };
}

With my interface I get the error outlined above. Why? Is java.lang.Comparable treated specially?

public void someThing()
{
    CustomComparable<Object> o = new CustomComparable<Object>()
    {
        public int compare(Object a, Object b)
        {
            // ...
        }
    };
}

I’m using Java 1.6u21 and NetBeans 6.9.1.

Answer 1

It looks like you want to use a Comparator<T> and not a Comparable<T> — the interface already exists.