Why can't I Insert my File object as comparable?

Question

I get an error in line with theTree.insert(new File("a", 1));: The method insert(Comparable) in the type Tree is not applicable for the arguments (File).

And when I try to cast as such theTree.insert((Comparable) new File("a", 1)); I get other error: Exception in thread "main" java.lang.ClassCastException: File cannot be cast to java.lang.Comparable at TreeApp.main(tree.java:134).

Why can't I pass this object?

My object:

class FileObject
{
    public String name;
    public int size;

    File(String a, int b)
    {
        this.name = a;
        this.size = b;
    }
}

Answer 1

You need to implement Comparable<File>

class File implements Comparable<File>
    {
        public String name;
        public int size;

        File(String passedName, int passedSize)
        {
            this.name = passedName;
            this.size = passedSize;
        }

        @Override
        public int compareTo(File o) {
            //e.g Provide comparable on size
            return Integer.valueOf(size).compareTo(o.size);
        }
    }

References:

• Comparable

Note: Please provide compareTo implementation in contract with equals method.