CODEWITHSUNDEEP
javadesign-patterns
sar
sar

Reputation: 1287

Design approach for multiple if else statement?

I have method which returns sql query as string. This method consider parameter 'level' , based on this parameter there are multiple if else statement like

   if(level.equals("A1")){
    // add some  field in query
   }
   else if (level.equals("A2"))
   {
    // add some  field  and logic in query
   }
   ..

   so on

In future number of levels are going to increase and I don`t want to write pesky if else statements so I am looking for cleaner and maintainable design approach for this scenario. I am thinking of strategy design pattern but not sure whether it is best for this scenario.

Upvotes: 0

Views: 356

Answers (2)

T.J. Crowder
T.J. Crowder

Reputation: 1073968

You have several options:

  1. if/else if as you've indicated.

  2. A switch statement.

  3. A Map with the keys being the level string and the values being references of a functional interface type (Runnable or an appropriate interface from java.util.function, or your own) you can initialize with method references, lambdas, anonymous class instances, or even concrete class instances as required.

Here's an example of that last option, using the most basic functional interface, Runnable, with method references:

import java.util.Map;
import java.util.HashMap;

public class Example {
    private Map<String, Runnable> handlers;

    public Example() {
        this.handlers = new HashMap<String, Runnable>();
        this.handlers.put("A1", this::a1action);
        this.handlers.put("A2", this::a2action);
    }

    private void a1action() {
        System.out.println("Action A1");
    }

    private void a2action() {
        System.out.println("Action A2");
    }

    public void handleAction(String action) {
        Runnable handler = this.handlers.get(action);
        if (handler == null) {
            System.out.println("No handler for '" + action + "'");
        } else {
            handler.run();
        }
    }

    public static void main(String[] args) throws Exception {
        Example ex = new Example();
        ex.handleAction("A1");
        ex.handleAction("A2");
        ex.handleAction("A3");
    }
}

Upvotes: 1

OldCurmudgeon
OldCurmudgeon

Reputation: 65793

You can use an enum to list the operations and use valueOf to work out which to use.

enum Levels {
    A1 {
        @Override
        void doSomethingToTheQuery(Query q) {
            // add some  field in query
        }
    },
    A2{
        @Override
        void doSomethingToTheQuery(Query q) {
            // add some  field  and logic in query
        }
    };

    abstract void doSomethingToTheQuery(Query q);
}

public void test() {
    // Lookup the level and do hack the query.
    Levels.valueOf("A1").doSomethingToTheQuery(q);
}

You can then add new levels just by adding to the enum.

Upvotes: 0

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