Switch statement for representations of Enum values ​​in Java

Question

I am very familiar with using Enums in other languages, but I have some difficulties with Java with specific use.

Sun's documentation for Enums boldly states:

"Java programming language variables are much more powerful than their counterparts in other languages, which are more than glorified integers."

Well, this dandy, but I need to have a constant representation of the data type for each of the Enums, for comparison in the switch statement. The situation is this: I am building nodes that will represent a given space or “slot” in the maze graph, and these nodes must be constructed from an array of 2D integers that represent the maze. Here is what I have for the MazeNode class that currently has a problem (switch barks statement):

NOTE. I know that this code does not work due to the dynamic element in the case expression. Here we can illustrate what I need.

public class MazeNode
{
    public enum SlotValue
    {
        empty(0),
        start(1),
        wall(2),
        visited(3),
        end(9);

        private int m_representation;

        SlotValue(int representation)
        {
            m_representation = representation;
        }

        public int getRepresentation()
        {
            return m_representation;
        }
    }

    private SlotValue m_mazeNodeSlotValue;

    public MazeNode(SlotValue s)
    {
        m_mazeNodeSlotValue = s;
    }

    public MazeNode(int s)
    {

        switch(s)
        {
            case SlotValue.empty.getRepresentation():
                m_mazeNodeSlotValue = SlotValue.start;
                break;
            case SlotValue.end.getRepresentation():
                m_mazeNodeSlotValue = SlotValue.end;
                break;

        }
    }

    public SlotValue getSlotValue()
    {
        return m_mazeNodeSlotValue;
    }

}

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, Enum 2D- .

Answer 1

- :

import java.util.HashMap;
import java.util.Map;

public class MazeNode {

    public enum SlotValue {
        empty(0), start(1), wall(2), visited(3), end(9);

        protected int m_representation;

        SlotValue(int representation) {
            m_representation = representation;

        }

        private static final Map<Integer, SlotValue> mapping = new HashMap<Integer, SlotValue>();

        static {
            for (SlotValue slotValue : SlotValue.values()) {
                mapping.put(slotValue.m_representation, slotValue);
            }
        }

        public static SlotValue fromRepresentation(int representation) {
            SlotValue slotValue = SlotValue.mapping.get(representation);
            if (slotValue == null)
                // throw your own exception
                throw new RuntimeException("Invalid representation:" + representation);
            return slotValue;
        }
    }

    private SlotValue m_mazeNodeSlotValue;

    public MazeNode(SlotValue s) {
        m_mazeNodeSlotValue = s;
    }

    public MazeNode(int s) {
        m_mazeNodeSlotValue = SlotValue.fromRepresentation(s);

    }

    public SlotValue getSlotValue() {
        return m_mazeNodeSlotValue;
    }

    public static void main(String[] args) {
        MazeNode m = new MazeNode(2);
        System.out.println(m.getSlotValue());
        m = new MazeNode(9);
        System.out.println(m.getSlotValue());
    }

}

Answer 2

, , :

public class MazeNode {
    private static final Map<Integer, SlotValue> mapping = new HashMap<Integer, SlotValue>();

    enum SlotValue {
        empty(0),start(1),wall(2),visited(3),end(9);

        private final int m_representation;

        SlotValue(int representation) {
            m_representation = representation;
            mapping.put(Integer.valueOf(representation), this);
        }

    }

    SlotValue getSlotValue(int representation) {
        return mapping.get(Integer.valueOf(representation));
    }

}

Answer 3

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decode() SlotValue. m_representation SlotValue . , , .

public class MazeNode {
    public enum SlotValue {
        empty(0),
        start(1),
        wall(2),
        visited(3),
        end(9);

        private int m_representation;

        SlotValue(int representation) {
            m_representation = representation;
        }

        private static SlotValue decode( int in ) {
            for ( SlotValue slot : values() ) {
                if ( slot.m_representation == in ) {
                    return slot;
                }
            }
            return empty;
        }
    }

    private SlotValue m_mazeNodeSlotValue;

    public MazeNode(SlotValue s) {
        m_mazeNodeSlotValue = s;
    }

    public MazeNode(int s) {
        m_mazeNodeSlotValue = SlotValue.decode( s );
    }

    public SlotValue getSlotValue() {
        return m_mazeNodeSlotValue;
    }
}

Answer 4

olliej, , , . Java ( #) (int ) . (m_representation ) , .

( ) ( , ) , . , , , .

, , , .

public enum SlotValue
{
    empty(0),
    start(1),
    wall(2),
    visited(3),
    end(9);

    private int m_representation;

    SlotValue(int representation)
    {
        m_representation = representation;
    }

    public static SlotValue fromInt(int intSerialization)
    {
        for(SlotValue sv : SlotValue.values())
            if(sv.m_representation == intSerialization)
                return sv;
        return null;
    }
}

private SlotValue m_mazeNodeSlotValue;

public MazeNode(SlotValue s)
{
    m_mazeNodeSlotValue = s;
}

public MazeNode(int s)
{
    m_mazeNodeSlotValue = SlotValue.fromInt(s);
}

Answer 5

( JS, : D) , switch .

? SlotValue int, getter SlotValue.

Answer 6

:

public class Node {
    public enum Slot {
        empty, start, wall, visited, end;
        static Slot fromInt(int s) {
            for (Slot slot : Slot.values())
                if (slot.ordinal() == s)
                    return slot;
            throw new RuntimeException("" + s + " is illegal value!");
        }
    }
    public Node(Slot slot) {
        this.slot = slot;
    }
    public Node(int s) {
        this(Slot.fromInt(s));
        switch(slot) {
            case empty: /* special stuff for empty */ break;
            case start: /* special stuff for start */ break;
            /* ... */
        }
    }
    private Slot slot;
}

Answer 7

, SlotValue , , . enum . , enum / , .

: ( , C enums), , " ". , , enum . , , enum ( 0, start is 1 ..).

, :

public class MazeNode
{
   public enum SlotValue
   {
       empty(0),
       start(1),
       wall(2),
       visited(3),
       end(9);

       private int m_representation;

       SlotValue(int representation)
       {
           m_representation = representation;
       }

       public int getRepresentation()
       {
           return m_representation;
       }

       private SlotValue next = null;

       static
       {
          empty.next = start;
          end.next = end;
       }
   }


   private SlotValue m_mazeNodeSlotValue;

   public MazeNode(SlotValue s)
   {
       m_mazeNodeSlotValue = s;
   }

   public MazeNode(int s)
   {
       m_mazeNodeSlotValue = SlotValue.values()[s].next;
   }

   public SlotValue getSlotValue()
   {
       return m_mazeNodeSlotValue;
   }
}