The LongAdder class in Java is a thread-safe utility that is used to incrementally accumulate a sum of long values. It is often used in scenarios where multiple threads are concurrently adding to the sum and the performance of the operation is critical. The LongAdder class provides a few different methods for performing these operations, one of which is the increment() method.

The increment() method is used to increment the current value of the LongAdder instance by one. It does so in a thread-safe manner by using a lock-free algorithm that reduces contention between threads. When multiple threads call the increment() method concurrently, the LongAdder instance will automatically partition the sum into multiple cells, with each thread operating on a separate cell. This helps to reduce contention between threads and improve the overall performance of the operation.

The increment() method returns void and has no parameters. To retrieve the current value of the sum, you can call the LongAdder's sum() method. If you need to increment the sum by more than one, you can use the add() method which takes a long value as a parameter and increments the sum by that value.

Overall, the LongAdder class and its increment() method provide a reliable and performant solution for accumulating sums of long values in concurrent environments.