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public class Main {
    public static void main(String[] args) {
        Thread1 thread1 = new Thread1();
        Thread2 thread2 = new Thread2();
        thread1.start();
        thread2.start();
    }

    static class FooTest {
        static volatile int x = 1;
        public synchronized static void foo1() {
            while (true) {
                x = -x;
            }
        }
        public static void foo2() {
            System.out.println("x = " + x);
        }
    }

    static class Thread1 extends Thread {
        @Override
        public void run() {
            FooTest.foo1();
        }
    }
    static class Thread2 extends Thread {
        @Override
        public void run() {
            while (true) {
                FooTest.foo2();
            }
        }
    }

}