java.concurrent.ReentrantLock - why we want to acquire the same lock multiple times [duplicate]

Answer 1

Consider this synchronized example. The same applies to lock but with more code.

synchronized int getSum() {
     return getValue() + getOtherValue();
}

synchronized int getValue() {
     return value;
}

synchronized int getOtherValue() {
     return value;
}

The only way to avoid being re-entrant is to create locked and unlocked versions of each method. However what if you have two instances A and B. A calls B which calls A. How does B know not to call a synchronized method in A.