Enum.java

package polyglot.util;

import java.io.Serializable;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.IOException;
import java.util.*;

/** An enumerated type.  Enums are interned and can be compared with ==. */
public class Enum implements Serializable
{
    /** The name of the enum.  Used for debugging and interning. */
    private String name;

    /** The intern cache. */
    private static Map cache = new HashMap();

    protected Enum(String name) {
	this.name = name;

        // intern the enum and make sure this one is unique
        if (intern() != this) {
            throw new InternalCompilerError("Duplicate enum \"" + name + "\"");
        }
    }

    /** For serialization. */
    private Enum() { }

    public int hashCode() {
        return name.hashCode();
    }

    public boolean equals(Object o) {
	return this == o;
    }

    public String toString() {
	return name;
    }

    private static class EnumKey {
	Enum e;

	EnumKey(Enum e) {
	    this.e = e;
	}

	public boolean equals(Object o) {
	    return o instanceof EnumKey
	        && e.name.equals(((EnumKey) o).e.name)
	        && e.getClass() == ((EnumKey) o).e.getClass();
	}

	public int hashCode() {
	    return e.getClass().hashCode() ^ e.name.hashCode();
	}

        public String toString() {
            return e.toString();
        }
    }

    public Enum intern() {
        EnumKey k = new EnumKey(this);

	Enum e = (Enum) cache.get(k);

	if (e == null) {
	    cache.put(k, this);
	    return this;
	}

	return e;
    }
}