Question

I am writing an Agent in Java that receives requests for its services from various other objects in the program. The restriction is that only one process can be done at once, which means that a PriorityQueue is probably the best way to represent requests for its services.

Unfortunately, these processes are stored as a enum with many different states. Is there an easy way to write a Comparator to order these states in the way I want? That is,

public enum AgentProcess
{
    ACTION1, ACTION2, ACTION3, ACTION4, ACTION20
}

with some Comparator

public class ProcessComparator<Process>
{
    public int compare(Process a, Process b)
    {
        //some arbitrary ordering of the processes, e.g., ACTION3 > ACTION19 > ACTION4...
    }
}

I’m currently stuck with doing something like

public static int getValue(Process p)
{
    switch(p)
    case ACTION1:
         return 5;
    case ACTION2:
         return 29;
    case ACTION3:
         return 18;
    //etc
}

Is there a way I could rewrite my enum so that it is naturally ordered, without having to define weights or a switch for each?

Answer 1

Three solutions come to my mind:

1. You specify the enum constants in the order you need and use p.ordinal() in the comparator.
2. You specify ordering index as a parameter for the enum constant, e.g. ACTION1(3), ACTION2(4), ACTION3(1), and provide a constructor in the enum that stores the parameter to a field, which you use in the comparator.
3. Create a list of Processes where you add all the constants in the order you want, and then use list.indexOf in the comparator. This is slower than approach 1 or 2, but that might not be a problem depending where you are using it.