Sun | Friday, September 30, 2011

Tip#10 Technique for making your class Immutable

Immutable classes are great.  You never have to worry about concurrency problems.  It also makes the code more readable - if a variable is final you don't have to look around for the other places where it gets modified -- there aren't any. Also the compiler will help you.  If you forget to assign a final variable it's a compile error.  It's also an error to try and reassign it.

Here is a simple trivial technique for setting final variables from a constructor where you need to do processing first.  The point is that you use temp variables to get your final values all lined up.  Then you assign the final values once.

I'll just let the code write the rest of this blog:

public final class DcomInfo {
    private final WindowsCredentials credentials;
    private final Node node;
    private final String password;
    private final String host;
    private final String user;
    private final String windowsDomain;
    private final String remoteNodeRootDirectory;

    public DcomInfo(Node theNode) throws WindowsException {
        node = theNode;

        if (node == null)
            throw new WindowsException(
                    Strings.get("internal.error", "Node is null"));

        if (!isDcomNode(node))
            throw new WindowsException(Strings.get("not.dcom.node",
                    getNode().getName(), getNode().getType()));

        SshConnector conn = node.getSshConnector();
        if (conn == null)
            throw new WindowsException(Strings.get("no.password"));

        SshAuth auth = conn.getSshAuth();
        if (auth == null)
            throw new WindowsException(Strings.get("no.password"));

        String notFinal = auth.getPassword();
        if (!ok(notFinal))
            throw new WindowsException(Strings.get("no.password"));

        password = DcomUtils.resolvePassword(notFinal);

        notFinal = node.getNodeHost();
        if (!ok(notFinal))
            notFinal = conn.getSshHost();
        if (!ok(notFinal))
            throw new WindowsException(Strings.get(""));
        host = resolver.resolve(notFinal);

        notFinal = auth.getUserName();
        if (!ok(notFinal))
            notFinal = System.getProperty("");
        if (!ok(notFinal))
            throw new WindowsException(Strings.get("no.username"));
        user = resolver.resolve(notFinal);

        notFinal = node.getWindowsDomain();
        if (!ok(notFinal))
            notFinal = host;
        windowsDomain = resolver.resolve(notFinal);

        notFinal = node.getInstallDirUnixStyle();
        if (!ok(notFinal))
            throw new WindowsException(Strings.get("no.lib.dir"));

        if (!notFinal.endsWith("/"))
            notFinal += "/";

        notFinal += SystemPropertyConstants.getComponentName();
        remoteInstallRoot = StringUtils.quotePathIfNecessary(notFinal);
        notFinal += "/lib";
        notFinal = StringUtils.quotePathIfNecessary(notFinal);
        notFinal = notFinal.replace('/', '\\');
        nadminParentPath = notFinal;
        nadminPath = notFinal + "\\nadmin.bat";

        String notFinal2 = node.getNodeDirAbsolute();

        if (notFinal2 == null) {
            // no special nodedir -- use the defaults
            notFinal2 = remoteInstallRoot;  // e.g. "d:/glassfish3/glassfish"
            notFinal2 += "/nodes";
        notFinal2 = notFinal2.replace('/', '\\');

        if (!notFinal2.endsWith("\\"))
            notFinal2 += '\\';

        remoteNodeRootDirectory = notFinal2 + node.getName();

        credentials = new WindowsCredentials(getHost(), getWindowsDomain(),
                getUser(), getPassword());

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