When and How to Use CountDownLatch and CyclicBarrier in Java

Official Explanation

Translation

CountDownLatch is a synchronization aid that allows one or more threads to wait until a set of other threads have completed their operations before proceeding.

CyclicBarrier is a synchronization aid that allows a group of threads to wait for each other at a common barrier point before continuing.

Personal Understanding: CountDownLatch

I think of it as a countdown lock.

Scenario Reconstruction

Imagine a final exam where the invigilator distributes the papers and waits while students finish; only after the last student submits does the teacher start processing the exams.

Additional Scenario

In a game of League of Legends, ten players load the game, but the last player cannot finish loading; the system waits until all players are ready before displaying the game.

Abstract Diagram

Personal Understanding: CyclicBarrier

It can be seen as a barrier that all threads must reach before they can all pass together.

Scenario Reconstruction

During a company outdoor team‑building activity, everyone must climb over a four‑meter wall without any handholds; the group can only proceed once every participant, including the boss, has successfully crossed.

Abstract Diagram

This explanation aims to help you grasp the typical use cases of these two synchronization tools; for detailed API usage, refer to the official Java documentation or search online.