Calling a method from user input in JAVA

Question

I'm looking for a way to call any given method in my class without having to do the whole try-catch statement.

EXAMPLE:

public void Worker(String handle) throws Exception
{
    if(PROTOCOL.contains(handle)) 
    {
        System.out.println("good");
        Worker.handle;
    }
    else { 
            throw new Exception("Don't understand <" + handle + ">");
         }
}

PROTOCOL is a list of allowed commands.

I know I can say if(input = ....){do....} but I want to be able to do the above; call my class with the input value.

Is this possible?

Answer 1

Depending on what your commands would look like you could use a Map<String, Command> which you'd then use like this:

Map<String, Command> PROTOCOL = ... //you build that map somehow

Command c = PROTOCOL.get(handle);
if( c != null ) {
    System.out.println("good");
    c.execute();
} else { 
    throw new Exception("Don't understand <" + handle + ">");
}

Command could then be a class or function interface:

interface Command {
  void execute();
}

Used as a class interface

class MyCommand implements Command {
  //this can have private data

  void execute() {
    //do whatever is needed
  }
}

PROTOCOL.put("mycommand", new MyCommand(/*you could pass parameters here*/));

Advantages:

• The interface can have more than 1 method, e.g. it could have a String getName() as well.
• Commands can have parameters, e.g. you could provide one implementation and use different names that are bound to the same command with different parameters (e.g. a "increment" and "decrement" could be bound to AddCommand(1) and AddCommand(-1)).
• You could use some dependency inversion mechanism (e.g. via CDI) to have commands register themselves to PROTOCOL. That way you could even add commands via some plugin mechanism.
• Using interfaces for classes might be easier to grasp for others.
• Easier to structure for larger commands as you can easily extract the classes into separate files.

Used as a function interface (e.g. via lambdas)

PROTOCOL.put("mycommand", () -> { 
  //do whatever is needed
});

Advantages:

• No classes needed which can be more concise for short commands.