The main differences between IO and NIO in Java are as shown in the figure:
1. Stream-oriented and buffer-oriented
IO is stream-oriented, and NIO is buffer-oriented.
Java IO is stream-oriented meaning that one or more bytes are read from the stream at a time until all bytes are read, and they are not cached anywhere.
Java NIO's buffer-oriented approach is slightly different. The data is read into a buffer that it processes later, moving back and forth in the buffer as needed.
2. Blocking and non-blocking IO
The various streams of Java IO are blocking. When a thread calls read() or write(), the thread is blocked until some data is read, or the data is completely written.
The non-blocking mode of Java NIO allows a thread to send a request to read data from a certain channel, but it can only get the currently available data. If no data is currently available, nothing will be obtained. Instead of keeping the thread blocked, the thread can continue to do other things until the data becomes readable.
3. Selector
Java NIO's selector allows a single thread to monitor multiple input channels. You can register multiple channels using one selector. A separate thread is then used to "select" channels that already have input that can be processed, or select channels that are ready to be written to. This selection mechanism makes it easy for a single thread to manage multiple channels.
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