What is the principle of concurrent execution in Java?

The principle of concurrent execution in Java is implemented through the use of multi-threading. Each thread in Java functions as an independent execution path, allowing for concurrent execution of different tasks. On multi-core processors, multiple threads can execute simultaneously, thus improving the efficiency of program operation.

Java supports multithreading, allowing users to create a new thread by creating a Thread object and calling the start() method. Each thread in a multithreaded environment has its own program counter, stack, local variables, and registers. Threads independently execute their tasks and switch between them using a context-switching mechanism.

The main principles of Java concurrency execution include the following aspects:

1. Thread Scheduling: In Java, the thread scheduler is responsible for determining when each thread should execute and for how long. With the scheduler, it is possible to switch threads and allocate CPU time slices, allowing multiple threads to run concurrently.
2. Lock Mechanism: Java provides synchronized keywords and Lock interface and other locking mechanisms to achieve mutual exclusion between threads accessing shared resources. With the lock mechanism, it ensures that only one thread can access shared resources at a time, thus avoiding data race and thread safety issues.
3. Memory Model: Java’s memory model defines the visibility and ordering rules of shared variables between threads. By using mechanisms such as the volatile keyword, synchronized keyword, and atomic classes, data consistency and thread safety between threads can be ensured.
4. Inter-thread communication: Java provides methods such as wait(), notify(), and notifyAll() for threads to wait and be awakened. These methods allow multiple threads to coordinate execution, enabling communication and synchronization between threads.

In conclusion, the principle behind Java’s concurrent execution is achieved through the use of multiple threads, along with mechanisms such as thread scheduling, locking, memory model, and inter-thread communication to ensure the concurrent execution of threads and consistency of data.