Quiz leaderboard with chained comparators

import java.util.*;

public class Main {
    private static final Scanner IN = new Scanner(System.in).useLocale(Locale.ROOT);

java.util.* imports utility type names such as Scanner, Locale and collections. Main is the public class matching Main.java. The private static final IN field holds one shared Scanner for System.in; final prevents replacing that reference. The scanner uses Locale.ROOT.

    static String text() {
        if (!IN.hasNextLine()) throw new IllegalArgumentException("Incomplete input.");
        String value = IN.nextLine().trim();
        if (value.isEmpty() || value.length() > 200) throw new IllegalArgumentException("Text must have 1–200 characters.");
        return value;
    }

text checks whether a line exists, reads it and removes leading/trailing whitespace. Reject empty text and lengths above 200 by throwing IllegalArgumentException. Otherwise return the string. One field is read per line, so these helpers do not mix nextInt with leftover newlines.

    static int integer(int low, int high) {
        int value = Integer.parseInt(text());
        if (value < low || value > high) throw new IllegalArgumentException("Integer out of range.");
        return value;
    }

Integer.parseInt converts the returned string to int or throws NumberFormatException, a subtype of IllegalArgumentException. Reject values outside the caller’s inclusive low/high limits, then return the accepted integer.

    static double number(double low, double high) {
        double value = Double.parseDouble(text());
        if (!Double.isFinite(value) || value < low || value > high) throw new IllegalArgumentException("Number out of range.");
        return value;
    }

Double.parseDouble reads the string as a double. Double.isFinite rejects NaN and infinities as well as the explicit low/high range check. Return only a finite accepted value; exceptions transfer control to a matching catch block.

    static void money(String label, double value) { System.out.printf(Locale.ROOT, "%s: %.2f%n", label, value); }

money is a formatting helper: %s prints the label, %.2f prints two decimal places, and %n ends the line. Locale.ROOT fixes locale-sensitive formatting. The helper can also display non-currency quantities; it does not change the stored value.

static class Player {
        final String name;final int score;final double timeTaken;
        Player(String name,int score,double time){this.name=name;this.score=score;timeTaken=time;}
    }

Each Player stores a name, score and time taken in final fields. The constructor assigns the accepted input values.

    static final Comparator<Player> ORDER=Comparator.comparingInt((Player p)->p.score).reversed().thenComparingDouble(p->p.timeTaken).thenComparing(p->p.name);

Compare score descending, then completion time ascending, then name in String natural order. The second and third rules are used only when earlier comparisons tie.

    static class Leaderboard {
        final ArrayList<Player> players=new ArrayList<>();
        void displayTop(){players.sort(ORDER);System.out.println("Top players:");for(int i=0;i<Math.min(5,players.size());i++){Player p=players.get(i);System.out.printf(Locale.ROOT,"%s | %d | %.2f seconds%n",p.name,p.score,p.timeTaken);}}

Leaderboard owns an ArrayList. displayTop sorts that list using ORDER, then visits only min(5,size) entries. It therefore also works with fewer than five or no players.

        String search(String name){for(Player p:players)if(p.name.equalsIgnoreCase(name))return Integer.toString(p.score);return "No such Player";}

Scan players and use equalsIgnoreCase for identity matching. Return the found score as text, or the explicit absent-player message.

        String delete(String name){Iterator<Player> it=players.iterator();while(it.hasNext())if(it.next().name.equalsIgnoreCase(name)){it.remove();return "SUCCESS";}return "No such Player";}
    }

Use Iterator.remove immediately after next identifies a matching player. This safely removes the current entry during traversal. Return SUCCESS after one removal, or the absent message after the full scan.

    // n; name/score/time for each. Then 1=top five, 2 name=search, 3 name=delete, 0=exit.
    public static void main(String[] args){
        try{
            int n=integer(0,50);Leaderboard board=new Leaderboard();
            for(int i=0;i<n;i++){String name=text();int score=integer(0,10000);double time=number(0,1000000);if(!board.search(name).equals("No such Player"))throw new IllegalArgumentException("Duplicate player name.");board.players.add(new Player(name,score,time));}

Read up to 50 players with checked scores and finite times. The existing search rule prevents duplicate names even with different letter case. Add only accepted new Player objects.

            while(true){int command=integer(0,3);if(command==0)break;if(command==1)board.displayTop();else if(command==2)System.out.println(board.search(text()));else System.out.println(board.delete(text()));}
        }catch(IllegalArgumentException e){System.out.println("Invalid input: "+e.getMessage());}
    }
}

Command 0 ends the session. Other commands call the corresponding Leaderboard method; search and delete read an additional name line. The catch reports malformed or out-of-range input.