Good Ol' Switch Statements

Switch statements have been around since the early days of programming. In fact, the structure is identical across C-style languages.

switch (variable) {
    case 1:
        // Some code here
        break;
    case 2:
        // Some code here
        break;
    default:
        // Some code here
        break;
}

I’ve almost always had to have break statements between the cases. This is because I usually use a switch to replace multiple IF statements.

When I created one of my first Android apps, there are some common use cases like:

1. First time installed of version 1

2. Update from version 1 to version 2

3. Delayed update from version 1 to version 3+

The way Android handled this back then was clever to me and was the first time I used a switch without breaks. Please see a short example below:

@Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

        switch(oldVersion)
        {
            case 1:
                db.execSQL(ADD_NEW_RECORDS);
            case 2:
                db.execSQL(CREATE_NEW_TABLE);
                db.execSQL(CREATE_ANOTHER_NEW_TABLE);
            case 3:
                db.execSQL(ALTER_TABLE);
                break;
            default:
                //log no update applied
        }
    }

The way this code works is like so:

We know it is an upgrade because Android is calling the onUpgrade method. If the old database version is “1” (which corresponds to the first release), this app is behind a couple of version. The switch matches on “1” and executes the SQL in the constant variable to add some values to a table. Since the first case doesn’t have a break, it drops through and creates some new tables, and then finally alters the schema of another table.

If the app was already on version 3 of the database, the switch skips the database changes that the this version of the app presumably already has and just runs the alter table SQL.

While I found this use cases with a switch interesting, I imagine there are better ways to apply conditional transformations to a system, but this way is straightforward and easy to understand.