asking user for input valid command in java

Question

I am developing my own shell(command prompt). [When
a user enters a built-in command, the shell is required to search and execute the respective code accordingly.]

I have created my code using command split, and command parameters in order to store my commands. but one thing I'm confused about is that making a command that is not in the list. I think of using if statement to print invalid comment (for example)

if (command!="exit")||(command!="about")||(command!="date")||(command!="time")||(command!="hist")||(command!="notepad")
                    ||(command!="")||(command!="hist -h")||(command!="hist -l")||(command!="c"){

System.out.println("invalid command");
}

but this statement is way too much if there are tons of command line.. so is there an easy way of implementing it !?

Dhawal Kapil · Accepted Answer · 2018-05-02 17:12:32Z

1

If this java and all commands are Strings and input command is also a String you can simplify what you are trying to do by creating a list of valid commands and do a contains check.

List<String> validCommands = Arrays.asList("exit", "about", "date");
if (!validCommands.contains(command)) {
    System.out.println("invalid command");
}

That being said there are better ways to maintain a list of valid command outside java program such as properties file and load list of valid commands from that file. This will make your program more maintainable.

answered May 2, 2018 at 17:12

Dhawal Kapil

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2 Comments

Hans Hong Over a year ago

What if command includes integer for example.. like if i want to print previous x number of used commands, ill be using (hist x) as X indicates integer number of used commands.. and hist = history of commands

Dhawal Kapil Over a year ago

hist x will still be a string, string combined with integer can be cast to a string

Andrew S · Accepted Answer · 2018-05-02 17:16:04Z

0

Use a Map<String, Command>, to keep track of the available commands. If the command is not in the map then it's invalid. For example:

public class Shell {
    private final Map<String, Command> supportedCommands;

    public Shell(Map<String, Command> supportedCommands) {
        this.supportedCommands = supportedCommands;
    }

    public void execute(String command, String[] args) {
        Command c = supportedCommands.get(command);
        if (c == null) {
            System.out.println("invalid command");
        } else {
            c.execute(args);
        }
    }


    public interface Command {
        public void execute(String[] args);
    }

}

answered May 2, 2018 at 17:16

Andrew S

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1 Comment

Hans Hong Over a year ago

same issue as above solution (((((What if command includes integer for example.. like if i want to print previous x number of used commands, ill be using (hist x) as X indicates integer number of used commands.. and hist = history of commands )))))

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