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Thread: Alternative to Enum

  1. #1
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    Question Alternative to Enum

    Okay, on the common library I work on I have a database system, with implementations of MySQL and SQLite.
    Because I like reusing code I use PreparedStatements like this.
    I got the Statement enum:
    public enum Statement {
        // just an example
        SELECT("SELECT '?' FROM '?';");
     
    	private String statement = null;
     
    	Statement(String statement) {
    		this.statement = statement;
    	}
     
    	public String getStatement() {
    		return statement;
    	}
    }
    And then I have the MySQL executeStatement:
    public int executeStatement(Statement statement, Object... args) {
    	try {
    		PreparedStatement ps = conn.prepareStatement(statement.getStatement());
    		statementsPrepared++;
    		Logger.log(LogLevel.DEBUG, String.format("Prepared statement(%s): %s", statementsPrepared, statement.name()));
    		for(int i = 1; i<args.length; i++)
    		{
    			ps.setObject(i, args[i]);
    		}
    		Logger.log(LogLevel.DEBUG, String.format("Set %s objects for statement(%s)", args.length, statementsPrepared));
    		Logger.log(LogLevel.DEBUG, String.format("Executing statement(%s)", statementsPrepared));
    		return ps.executeUpdate();
    	} catch(SQLException e) {
    		Logger.log(LogLevel.ERROR, e.getMessage());
    		return e.getErrorCode();
    	}
    }
    Alright, so here's the thing, as this is a library I don't want to add new statements to the enum all the time, that just won't work.
    I've seen those posts around the web with a kind off dynamic enum, like the one there you implement the values() and valueOf() methods yourself. But they won't allow direct access like a real enum does, and that's what I want. Is there any approach for doing that?

    Thanks in advance.
    Last edited by Doctor X; October 6th, 2012 at 03:50 PM. Reason: Solved


  2. #2
    Super Moderator helloworld922's Avatar
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    Default Re: Alternative to Enum

    Let me understand what you want:

    You want an enum which allows you to access items directly by doing something like Statement.SELECT, but not have the definition of SELECT defined in the enum class?

    It's not possible because Statement.SELECT is evaluated at compile time, and if it's not available the compile will fail.

    Why can't you do something like this? You'll need to provide an external file which you can modify without recompiling your library.

  3. #3
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    Default Re: Alternative to Enum

    Thanks for the answer, I have read that thread before but it's not what I wanted to do.
    I ended up changing the Statement class to:
    public abstract class Statement {
     
    	private Object[] parameters = null;
     
    	protected Statement(Object... parameters) {
    		this.parameters = parameters;
    	}
     
    	public final Object[] getParameters() {
    		return parameters;
    	}
     
    	public abstract String getStatement();
    }

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