Java Language Implementing Basic Command-Line Behavior


Example

For basic prototypes or basic command-line behavior, the following loop comes in handy.

public class ExampleCli {

    private static final String CLI_LINE   = "example-cli>"; //console like string

    private static final String CMD_QUIT   = "quit";    //string for exiting the program
    private static final String CMD_HELLO  = "hello";    //string for printing "Hello World!" on the screen
    private static final String CMD_ANSWER = "answer";    //string for printing 42 on the screen

    public static void main(String[] args) {
        ExampleCli claimCli = new ExampleCli();    // creates an object of this class

        try {
            claimCli.start();    //calls the start function to do the work like console
        }
        catch (IOException e) {
            e.printStackTrace();    //prints the exception log if it is failed to do get the user input or something like that
        }
    }

    private void start() throws IOException {
        String cmd = "";
        
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        while (!cmd.equals(CMD_QUIT)) {    // terminates console if user input is "quit"
            System.out.print(CLI_LINE);    //prints the console-like string 

            cmd = reader.readLine();    //takes input from user. user input should be started with "hello",  "answer" or "quit"
            String[] cmdArr = cmd.split(" ");

            if (cmdArr[0].equals(CMD_HELLO)) {    //executes when user input starts with "hello"
                hello(cmdArr);
            }
            else if (cmdArr[0].equals(CMD_ANSWER)) {    //executes when user input starts with "answer"
                answer(cmdArr);
            }
        }
    }
    
    // prints "Hello World!" on the screen if user input starts with "hello"
    private void hello(String[] cmdArr) {
        System.out.println("Hello World!");
    }
    
    // prints "42" on the screen if user input starts with "answer"
    private void answer(String[] cmdArr) {
        System.out.println("42");
    }
}