To execute a.methodA(), Thread 1 will need to obtain the lock on the A object. It is possible that the execution of these two statements is interweaved: Thread 1: a.methodA(b) //inside the constructor What is it that causes this to go into a deadlock and workarounds? Even if they are, the synchronized keyword would queue them, wouldn't it? But how come this would occasionally enter a deadlock too? It is not all the time but it would sometimes enter a deadlock, which is quite unpredictable. There is no cross dependencies on any object and they are not executing a method at a same time too. At the same time, a.methodA(b) would call b.last(). It will call b.methodB(a), which then calls a.last() to just print out a statement.

When it does this, the run() method is invoked. In this case, when the Deadlock() constructor is called, it starts itself as a thread. The example was taken from Deadlock detection in Java: Class A

I've found one of the code on Stack Overflow and I thought it is pretty similar to what I am facing but I still don't understand why this would enter a deadlock.

Java deadlock detection