Using Volatile

Counter.java

package com.pivincii;

public class Counter {
    private volatile int count = 0;

    public void increment() {
        count ++;
    }

    public void decrement() {
        count --;
    }

    public int getCount() {
        return count;
    }

    public static void main(String[] args) {
        for (int i = 0; i < 100; i ++) {
            Counter counter = new Counter();
            new Thread(counter::increment).start();
            new Thread(counter::decrement).start();
            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(counter.getCount());
        }
    }
}