dowhile

package my.pack;

import java.util.Scanner;
import java.util.function.Function;

public class David1 {

    public static void main(String[] args) {
        String inputString = "hello";

        doWhile(new Function<String, Boolean>() {

            @Override
            public Boolean apply(String t) {
                if (t == null)
                    return false;

                return t.equals(inputString);
            }
        }, "input string should be " + inputString + ".");
    }

    public static void doWhile(Function<String, Boolean> conditionChecker, String errMsg) {
        Scanner s = new Scanner(System.in);

        String next = null;

        do {
            if (next != null)
                System.err.println(errMsg);

            next = s.nextLine();
        }
        while(!conditionChecker.apply(next));
    }


}