The past few posts have been going over some of the improvements that came with updating to Java 7. This article will showcase how to use strings in a switch statement using the carmix-creator project.

Prior to Java 7, you had to use constants of type Byte, Character, Short, Integer constants (or their primitive equivalents) or enums as values for the cases in a switch statement. Personally, I think this is the way to go, but it isn't always possible and I'm glad they made the change. The majority of my past projects made minimal use of enum or Integer/int constants. They relied heavily on Strings, so this change would help make an endless sea of if statements look a little bit better. Even in my own code, I've only started to embrace enums, but it'll be a while before I get to writing about all that.

The carmix-creator project has a method called verifyFile. It makes use of several if statements. It can be cleaned up some by switching some of the if statements with switch statements. Prior to Java 7, you could only use a switch statement with an integer or enumerated type. But now, we can use strings.

As an example of a method that could make use of this construct, here is the old version of the verifyFile method:

private boolean verifyFile(File aFile, String indFileDir, String indReadWrite) throws IOException {
    if (!aFile.exists()) {
        throw new IOException("File Verification: " + aFile.getPath() + " does not exist");
    }
    if (FILE_TYPE.equals(indFileDir)) {
        if (!aFile.isFile()) {
            throw new IOException("File Verification: " + aFile.getPath() + " does not exist");
        }
    } else if (DIR_TYPE.equals(indFileDir)) {
        if (!aFile.isDirectory()) {
            throw new IOException("Directory Verification: " + aFile.getPath() + " does not exist");
        }
    }
    if (READ_FILE.equals(indReadWrite)) {
        if (!aFile.canRead()) {
            throw new IOException("File Verification: Cannot read file " + aFile.getPath());
        }
    } else if (WRITE_FILE.equals(indReadWrite)) {
        if (!aFile.canWrite()) {
            throw new IOException("File Verification: Cannot write to file " + aFile.getPath());
        }
    }
    return true;
}

Updated:

private boolean verifyFile(File aFile, String indFileDir, String indReadWrite) throws IOException {
    if (!aFile.exists()) {
        throw new IOException("File Verification: " + aFile.getPath() + " does not exist");
    }
    switch (indFileDir) {
    case FILE_TYPE:
        if (!aFile.isFile()) {
            throw new IOException("File Verification: " + aFile.getPath() + " does not exist");
        }
        break;
    case DIR_TYPE:
        if (!aFile.isDirectory()) {
            throw new IOException("Directory Verification: " + aFile.getPath() + " does not exist");
        }
        break;
    default :
        break;
    }
    switch (indReadWrite) {
    case READ_FILE:
        if (!aFile.canRead()) {
            throw new IOException("File Verification: Cannot read file " + aFile.getPath());
        }
        break;
    case WRITE_FILE:
        if (!aFile.canWrite()) {
            throw new IOException("File Verification: Cannot write to file " + aFile.getPath());
        }
        break;
    default :
        break;
    }
    return true;
}

If you're interested, I did manage to make some other changes to this method by using the NIO.2 classes. These updates can be seen in GitHub.

Switch with strings may seem like a small change, but I can think of at least a dozen places it might be useful in some of the legacy code with which I have worked and I imagine most everyone could think of at least one area in which it would improve the code to some degree.