How to check for strings after a character in Java-CodePudding

I am trying to make it so anytime a user enters ."insert word here" the program will recognize this an invalid command and send the user a message saying something like "invalid command type .help for a list of commands". I already have my active commands working but Im not sure how to catch invalid commands here is my code so far.

while (true) {

 String userInput = scan.nextLine();
 
 if (userInput.equals(".help")) {

 //print list of commands
 }

 else if (userInput.equals(".ping") {
 //print pong
 }

 //check for any String that starts with . but does not equal the previous commands and return an error message
}

CodePudding user response：

You could use a switch statement to handle unknown commands:

while (true) {
    String userInput = scan.nextLine();

    switch(userInput) {
        case ".help":
            // print list of commands
            break;

        case ".ping":
            // print pong
            break;

        default:
            // print error message for unknown command
    }
}

CodePudding user response：

You can use the startsWith method to check if the user's input starts with a period, and then use the equals method to check if it is not equal to any of the valid commands. Here is an example:

while (true) {
  String userInput = scan.nextLine();

  if (userInput.equals(".help")) {
    // print list of commands
  } else if (userInput.equals(".ping")) {
    // print pong
  } else if (userInput.startsWith(".")) {
    System.out.println("Invalid command. Type .help for a list of commands.");
  }
}

CodePudding user response：

        while (true) {
            String userInput = scan.nextLine();
            if (userInput.equals(".help")) {
                //print list of commands
            } else if (userInput.equals(".ping")) {
                //print pong
            } else if(userInput.startsWith(".")) {
                // applies if userInput starts with "." but is not .help or .ping
            }
            else {
                // applies if userInput does not start with a "."
            }
        }