How to call a function with arguments from a String?

Question

If I have a String that contains a command and I want the program to read it and preform what it says.

example:

If I have a function:

private void move(float position, float speed){
.....
}

and a String

String command = "MOVE 305 5"

where the "MOVE" calls the move() function and “305“ is the position and the “5“ is the speed.

So, it should be like this:

move(305, 5);

How can I call the function using this String?

If all of your strings will be following the format of COMMAND arg1 arg2 argN then why not use String#Split? — px06
– px06, Commented Feb 2, 2017 at 10:14
You should learn about "reflection" in Java. With reflection you can use a string as input to invoke an existing method. — IQV
– IQV, Commented Feb 2, 2017 at 10:18
@IQV No reflection needed here. From experience, it should be avoided if possible. — Fildor
– Fildor, Commented Feb 2, 2017 at 10:22
@IQV true, but for something like this it's not a very optimal solution. This just requires some simple parsing. — Kayaman
– Kayaman, Commented Feb 2, 2017 at 10:22
user3879781 provided the move-command as an example. According to his profile he's interested in game-developing. So I think "move" will not be the only command, so it's necessary to use a broad approach. — IQV
– IQV, Commented Feb 2, 2017 at 10:25

Ofer Arial · Accepted Answer · 2017-02-02 17:27:55Z

5

If all of your commands are in the same format, you should have a switch statement, that will switch between the possible commands you may have. This way, you will call each function when it is needed with the args from the string.

Example:

String[] parts = command.split(' ');
switch(parts[0])
{
    case "MOVE":
        float position = Float.parseFloat(parts[1])
        float speed = Float.parseFloat(parts[2])
        move(position, speed);
        break;

    case ... :

    ...

    default:
        System.out.println("Unknown command");
        break;

}

edited Feb 2, 2017 at 17:27

answered Feb 2, 2017 at 10:18

Ofer Arial

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Comments

Arnaud · Accepted Answer · 2017-11-03 05:09:21Z

3

You may use an Enumeration for the different possible commands, along with a switch-case as already shown in other answers .

The enumeration :

 public enum CommandType{

        MOVE, STOP;
 }

And a sample usage :

String[] splitted = command.split("\\s");

CommandType currentCommand = CommandType.valueOf(splitted[0]);


switch(currentCommand){

    case MOVE : 
        move(Float.parseFloat(splitted[1]),Float.parseFloat(splitted[2]));
        break;
    case STOP : 
        stop();
        break;
    default :
        break;
}

edited Nov 3, 2017 at 5:09

answered Feb 2, 2017 at 10:26

Arnaud

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