Java While循环输入验证

Question

Hi I wonder if how can I put a validation on the while of if statements so the program will only execute if the user enters the commands "move" "line" "circle" with their parameters. For example if the user enters "move 200" the program will say Invalid because there's only one or NO parameter. Thanks!

import java.util.Scanner;

public class DrawingProgram1 {

public static void main(String[] args) {

    GraphicsScreen g = new GraphicsScreen();

    String store;
    String command;

    int move1;
    int move2;
    int line1;
    int line2;
    int circle;

    while (true) {
        Scanner scan = new Scanner(System.in);
        System.out.println("Type 'help' for list of commands. Type 'end' to finish.");
        System.out.println("Please enter a command:");
        store = scan.nextLine();
        String [] splitUpText = store.split(" ");
        command = splitUpText[0];


        if (command.equalsIgnoreCase("move")) {
            move1 = Integer.parseInt(splitUpText[1]);
            move2 = Integer.parseInt(splitUpText[2]);
            g.moveTo(move1, move2);

        }
        else if (command.equalsIgnoreCase("line")) {
            line1 = Integer.parseInt(splitUpText[1]);
            line2 = Integer.parseInt(splitUpText[2]);
            g.lineTo(line1, line2);
        }
        else if (command.equalsIgnoreCase("circle")) {
            circle = Integer.parseInt(splitUpText[1]);
            g.circle(circle);
        }
        else if (command.equalsIgnoreCase("help")) {
            System.out.println("Enter a command for move.");
            System.out.println("Enter a command for line.");
            System.out.println("Enter a command for circle.");
        }
        else if (command.equalsIgnoreCase("end")) {
            System.exit(0);
        }
        else {
            System.out.println("Error");
        }
    }   





}

}

Answer 1

In the case , add extra condition for if statement, for eg, you can say

if(command.equalsIgnoreCase("move") && splitUpText.length == 3){

 //do necessary actions
}

for move command, the array size should not be less than or greater than 3.

Add conditions for other if statements according to the parameters for each command.

Answer 2

You could have either the wrong number of arguments or invalid arguments. Use this to catch 'em all:

if (command.equalsIgnoreCase("move")) {
    try {
       move1 = Integer.parseInt(splitUpText[1]);
       move2 = Integer.parseInt(splitUpText[2]);
       g.moveTo(move1, move2);
    } catch (ArrayIndexOutOfBoundsException e1) {
       Sytem.out.println("Please specify 2 parameters!")
       continue;
    } catch (NumberFormatException e2) {
       Sytem.out.println("Invalid parameters!")
       continue;
    }
}

Answer 3

What if you wrap all those requests in Command objects? I think that the Command design pattern fits well in your case. Command pattern explanation

Answer 4

replace this

if (command.equalsIgnoreCase("move")) {
    move1 = Integer.parseInt(splitUpText[1]);
    move2 = Integer.parseInt(splitUpText[2]);
    g.moveTo(move1, move2);
}

whith

if (command.equalsIgnoreCase("move")) {
    try {
       move1 = Integer.parseInt(splitUpText[1]);
       move2 = Integer.parseInt(splitUpText[2]);
       g.moveTo(move1, move2);
    } catch (ArrayIndexOutOfBoundsException e) {
       Sytem.out.println("move needs 2 parameters!")
       continue;
    }
}

and apply this to your other commands.

Answer 5

You can use:

if (splitUpText.lenght() != 3)
    System.err.println("Invalid...");