public class PrintA_To_Z_2 { public static volatile int i = 0; public static Object obj = new Object(); public static boolean flag_A = true; public static boolean flag_B = false; public static boolean flag_C = false; static class PrintThread_A implements Runnable{ @Override public void run(){ while(i < 26){ if(flag_A){ synchronized (obj){ System.out.println(Thread.currentThread().getName() + (char)('A' + i)); ++i; flag_A = false; flag_B = true; } } } } } static class PrintThread_B implements Runnable{ @Override public void run(){ while(i < 26){ if(flag_B){ synchronized (obj){ System.out.println(Thread.currentThread().getName() + (char)('A' + i)); ++i; flag_B = false; flag_C = true; } } } } } static class PrintThread_C implements Runnable{ @Override public void run(){ while(i < 26){ if(flag_C){ synchronized (obj){ System.out.println(Thread.currentThread().getName() + (char)('A' + i)); ++i; flag_C = false; flag_A = true; } } } } } public static void main(String[] args) throws Exception{ Thread t1 = new Thread(new PrintThread_A(), "1"); Thread t2 = new Thread(new PrintThread_B(), "2"); Thread t3 = new Thread(new PrintThread_C(), "3"); t1.start(); t2.start(); t3.start(); t1.join(); t2.join(); t3.join(); System.out.println("OK"); } }