Ways to eliminate switch in code [closed]

Answer 1

See the Switch Statements Smell:

Typically, similar switch statements are scattered throughout a program. If you add or remove a clause in one switch, you often have to find and repair the others too.

Both Refactoring and Refactoring to Patterns have approaches to resolve this.

If your (pseudo) code looks like:

class RequestHandler {

    public void handleRequest(int action) {
        switch(action) {
            case LOGIN:
                doLogin();
                break;
            case LOGOUT:
                doLogout();
                break;
            case QUERY:
               doQuery();
               break;
        }
    }
}

This code violates the Open Closed Principle and is fragile to every new type of action code that comes along. To remedy this you could introduce a 'Command' object:

interface Command {
    public void execute();
}

class LoginCommand implements Command {
    public void execute() {
        // do what doLogin() used to do
    }
}

class RequestHandler {
    private Map commandMap; // injected in, or obtained from a factory
    public void handleRequest(int action) {
        Command command = commandMap.get(action);
        command.execute();
    }
}

If your (pseudo) code looks like:

class House {
    private int state;

    public void enter() {
        switch (state) {
            case INSIDE:
                throw new Exception("Cannot enter. Already inside");
            case OUTSIDE:
                 state = INSIDE;
                 ...
                 break;
         }
    }
    public void exit() {
        switch (state) {
            case INSIDE:
                state = OUTSIDE;
                ...
                break;
            case OUTSIDE:
                throw new Exception("Cannot leave. Already outside");
        }
    }

Then you could introduce a 'State' object.

// Throw exceptions unless the behavior is overriden by subclasses
abstract class HouseState {
    public HouseState enter() {
        throw new Exception("Cannot enter");
    }
    public HouseState leave() {
        throw new Exception("Cannot leave");
    }
}

class Inside extends HouseState {
    public HouseState leave() {
        return new Outside();
    }
}

class Outside extends HouseState {
    public HouseState enter() {
        return new Inside();
    }
}

class House {
    private HouseState state;
    public void enter() {
        this.state = this.state.enter();
    }
    public void leave() {
        this.state = this.state.leave();
    }
}

Hope this helps.