英文:
Use of Java non direct buffer
问题
Java有ByteBuffer。它有两种类型。一种是直接（direct），另一种是非直接（non-direct）。
直接缓冲区适用于IO。
当我们有byte[]时，为什么需要非直接ByteBuffer？什么时候使用它？
英文:
I did search a lot and checked multiple answers.. none of them is clear to me.
Java has ByteBuffer. It has 2 flavors. 1 is direct and the other one is non-direct.
The direct buffer is good for IO.
What is the need for non-direct bytebuffer when we have byte[]? When to use that?
答案1
得分: 2
非直接的ByteBuffer存储在堆上，并由底层字节数组支持。通常在需要可由Java应用程序进行读写的缓冲区，但不需要与直接ByteBuffer相同性能水平的情况下使用它们。<br>
那为什么不总是使用直接ByteBuffer呢？<br>
- 垃圾回收：非直接ByteBuffer受到垃圾回收的影响，当不再需要时，它可以自动释放内存。而对于直接ByteBuffer，您必须手动释放内存。
- 并发性：直接ByteBuffer不是线程安全的，需要显式同步才能被多个线程安全访问，这可能会给您的代码增加复杂性和开销。
- 复杂性：直接ByteBuffer通常需要更多的手动处理，可能涉及与本机代码一起工作，这可能会使它们比非直接ByteBuffer更复杂，更难处理。
- 增加的延迟：与非直接ByteBuffer相比，直接ByteBuffer可能具有增加的延迟，因为内存分配在Java堆之外，必须在本机堆和Java堆之间进行传输。
- 性能变化：直接ByteBuffer的性能取决于底层系统和硬件，这使得难以预测和保证性能。
英文:
non-direct ByteBuffers are stored in the heap and are backed by an underlying byte array. These are typically used when you need a buffer that is readable and writable by the Java application, but doesn't need the same level of performance as a direct ByteBuffer.<br>
So why not always use direct ByteBuffer?<br>
- Garbage Collection: Non-direct ByteBuffers are subject to garbage collection, which can free up memory automatically when it is no longer needed. With direct ByteBuffers, you have to manually free the memory.
- Concurrency: Direct ByteBuffers are not thread-safe and require explicit synchronization in order to be safely accessed by multiple threads, which can add complexity and overhead to your code.
- Complexity: Direct ByteBuffers often require more manual handling and can involve working with native code, which can make them more complex and harder to work with than non-direct ByteBuffers.
- Increased Latency: Direct ByteBuffers can have increased latency compared to non-direct ByteBuffers, as the memory is allocated outside of the Java heap and must be transferred to and from the native heap.
- Performance Variation: Performance with direct ByteBuffers can vary depending on the underlying system and hardware, making it harder to predict and guarantee performance.
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