Java synchronized detailed

It's important to write it down.

The Java language keyword that, when used to decorate a method or a block of code, guarantees that at most one thread executes the code at the same time.

First, when two concurrent threads access the same object in the synchronized (this) synchronization code block, only one thread can be executed within a single time. The other thread must wait for the current thread to finish executing the block before it can execute the code block.

Second, however, when a thread accesses one synchronized (this) of an object to synchronize a block of code, another thread can still access the non-synchronized (this) synchronous code block in the object.

Third, in particular, when a thread accesses one synchronized (this) of an object to synchronize a block of code, other threads will block access to all other synchronized (this) synchronization blocks in object.

The third example also applies to other synchronous blocks of code. That is, when a thread accesses a synchronized (this) of object to synchronize a block of code, it obtains the object lock of the objects. As a result, other threads are temporarily blocking access to all of the synchronization code portions of the object.

The above rules apply to other object locks as well.