checkers(idea)

package arina_dorofeeva;

public class Checkers {
    String colour;

}
package arina_dorofeeva;

public class Checker extends Checkers {
    private static class Field{
        static String letter;
        static int number;
    }
    protected void setSquare(String letter, int number) {
        if ((((int) (letter.charAt(0)) % 2 == 0) && number % 2 == 0) || (((int) (letter.charAt(0)) % 2 != 0) && number % 2 != 0)) {
            Field.letter = letter;
            Field.number = number;
        }
    }
    protected String getLetter() {
        return Field.letter;
    }
    protected int getNumber() {
        return Field.number;
    }

    protected void makeAMove(String l, int n ) {
        String letter = getLetter();
        int number = getNumber();
        int ascii = (int) letter.charAt(0);
        ascii += 1;
        letter = "" + (char) ascii;
        number += 1;
        if (l.equals(letter) && n == number)
            setSquare(letter, number);
        else {
            ascii -= 2;
            letter = "" + (char) ascii;
            if (l.equals(letter) && n == number)
                setSquare(letter, number);
        }
}
}

package arina_dorofeeva;

public class King extends Checkers {
    private static class Field{

        static String letter;
        static int number;
    }
    protected void setSquare(String letter, int number) {
        if ((((int) (letter.charAt(0)) % 2 == 0) && number % 2 == 0) || (((int) (letter.charAt(0)) % 2 != 0) && number % 2 != 0)) {
            Field.letter = letter;
            Field.number = number;
        }
    }
    protected String getLetter() {
        return Field.letter;
    }
    protected int getNumber() {
        return Field.number;
    }
    protected void makeAMove(String l, int n ) {
            String letter = getLetter();
            int number = getNumber();
            if ((int)letter.charAt(0)-(int)l.charAt(0)==n-number){
                setSquare(l,n);
            }
        }
    }

package arina_dorofeeva;

import java.io.PrintStream;
import java.util.Locale;
import java.util.Scanner;

public class Main {
    public static Scanner in = new Scanner(System.in);
    public static PrintStream out = System.out;
    public static void assertTrue(boolean condition){
        if (condition)
            return;
        else
            throw new AssertionError("Not correct!");
    }

    public static void main(String[] args) {
        in.useLocale(Locale.US);
        Checker check=new Checker();
        check.colour="light";
        check.setSquare("a",1);
        check.makeAMove("b",2);
        out.println(check.getLetter()+check.getNumber());
        King king=new King();
        king.colour="dark";
        king.setSquare("c",7);
        king.setSquare("h",1);
        out.println(king.getLetter()+king.getNumber());
        king.makeAMove("e",5);
        king.makeAMove("a",7);
        out.println(king.getLetter()+king.getNumber());
        out.println(check.colour+" "+check.getLetter()+check.getNumber());

    }
}