AtomicIntegerでsyncronized

ValueをAtomicValueに差し替え
int numをAtomicInteger numに差し替え
AtomicInteger#addAndGet()を使うことにより
排他をしなくても読み替えから足しこみまでをatomicに行う

これは発生しない
1st thread num ref
2nd thread num ref
1st thread num + 100

こういったかんじ
1st thread num ref and +100
2nd thread num ref and +100

class Value{
    int num;
    public void add(int num) {
        this.num += num;
    }
    public int get() {
        return num;
    }
}
class AtomicValue extends Value {
    AtomicInteger num = new AtomicInteger(0);
    @Override
    public void add(int num) {
        this.num.addAndGet(num);
        System.out.println("atomicvalue add method");
    }   
    public int get() {
        System.out.println("atomicvalue get method");
        return num.intValue();
    }
}
class Task implements Runnable {
    Value v;
    Task(Value v) {
        this.v = v;
    }
    @Override
    public void run() {
        this.v.add(100);
    }
}
public class Outer {
    public static void main(String[] args) {
        Value v = new AtomicValue();
        ExecutorService e = Executors.newFixedThreadPool(4);
        e.submit(new Task(v));
        e.submit(new Task(v));
        try {
            Thread.sleep(2000);
        } catch (InterruptedException ex) {
            ex.printStackTrace();
        }
        System.out.println(v.get());
        e.shutdown();
    }
}

atomicvalue add method
atomicvalue add method
atomicvalue get method
200