How to apply user defined try catch block in java

I am a beginner and I’ve finished the basic Nim game. Now I want to apply the try catch block to the program to make sure the flow control is perfect. However, the resources I’ve seen for now is to catch the exception in the main method that all the methods created must be called in the try block to catch the exception.

In my case, I create my class’s constructor to call the processCommands panel. Then, this panel calls the other methods in the class.

I need to catch the user input commands in the panel to see whether the commands is valid.

I’ve tried: https://beginnersbook.com/2013/04/user-defined-exception-in-java/

But it seems that I have to reconstruct the methods I’ve built so far. Is there any way to fix this?

Any help is appreciated. Thank you for your kindness and patience.

Here is part of my Nimsys:

import java.util.ArrayList;
import java.util.Scanner;

class InvalidUserInput extends Exception {
public InvalidUserInput(String s) {
    super(s);
}
}

public class Nimsys{

private NimModel nimModel;

public static void main(String[] args) throws InvalidUserInput {
    Nimsys nimsys = new Nimsys();
    nimsys.processCommands();
}


public Scanner in = new Scanner(System.in);

private void processCommands() {
    this.nimModel = new NimModel();
    System.out.println("Welcome to Nimn");
    while (true) {
        System.out.print('$');
        String [] commandin = in.nextLine().split(" ");

        if (commandin[0].equalsIgnoreCase("addplayer")) {
            addPlayer(commandin[1]);
        }
        if (commandin[0].equalsIgnoreCase("removeplayer")) {
            if (commandin.length > 1) {
                removePlayer(commandin[1]);
            } else {
                removePlayer("");
            }
        }
        if (commandin[0].equalsIgnoreCase("editplayer")) {
            editPlayer(commandin[1]);
        }
        if (commandin[0].equalsIgnoreCase("displayplayer")) {
            if (commandin.length > 1 ){
                displayPlayer(commandin[1]);
            } else {
                displayPlayer("");
            }

        }
        if (commandin[0].equalsIgnoreCase("startgame")) {
            startGame(commandin[1]);
        }
        if (commandin[0].equalsIgnoreCase("resetstats")) {
            if (commandin.length > 1 ){
                resetStats(commandin[1]);
            } else {
                resetStats("");
            }
        }

        if (commandin[0].equalsIgnoreCase("rankings")) {
            if (commandin.length > 1 && commandin[1].equals("asc")) {
                rankings(commandin[1]);
            }
            else if (commandin.length > 1 && commandin[1].equals("desc")) {
                rankings(commandin[1]);
            } else {
                rankings("");
            }  
        }

        if (commandin[0].equalsIgnoreCase("exit")) {
            if (commandin.length == 1) {
                System.out.println("");
                break;
            }
        }
    }
}

void userCommandCheck(String [] command) throws InvalidUserInput {
    if (command.length >2) {
        throw new InvalidUserInput("Incorrect number of arguments supplied to command.");
    }
    String [] commandSet = {"addplayer", "removeplayer", "editplayer", "displayplayer", "startgame", "resetstats", "rankings"};
    for(String commandCell: commandSet) {
        if (command[0] != commandCell) {
            throw new InvalidUserInput("`"+command[0]+"'" + " is not a valid command.");
        }
    }
}
}

Answer

private void processCommands() {
    this.nimModel = new NimModel();
    System.out.println("Welcome to Nimn");
    while (true) {
        System.out.print('$');
        String [] commandin = in.nextLine().split(" ");

        try {
            switch (userCommandCheck(commandin[0])) {
                case "addplayer":
                    addPlayer(commandin[1]);
                default:

            }
        } catch (InvalidUserInput e) {

        }
}

static String userCommandCheck(String command) throws InvalidUserInput {

    String [] commandSet = {"addplayer", "removeplayer", "editplayer", "displayplayer", "startgame", "resetstats", "rankings"};
    for(String commandCell: commandSet) {
        if (command.equalsIgnoreCase(commandCell)) {
            return command.toLowerCase();
        }
    }
    throw new InvalidUserInput("`"+command+"'" + " is not a valid command.");
}

}

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Answer