What does flush mean in java?

flush() is a method in the output stream class, used to force the data in the buffer to be flushed to the persistent storage device to avoid buffer data loss. Its usage is outputStream.flush().

flush() in Java

What is flush()?

flush() method is used to force the data in the buffer to be flushed to the persistent storage device.

The role of flush()

In Java, output operations usually use the buffering mechanism, that is, the data will be written to the buffer first instead of immediately to a file or other output device. This is to improve performance because the buffering mechanism reduces I/O operations to the output device.

However, the buffering mechanism also has a disadvantage: if the program terminates unexpectedly before the buffer data is written to the output device, the data in the buffer will be lost. To avoid this, you can use the flush() method, which forces the data in the buffer to be written to the output device immediately.

How to use flush()

The flush() method is the method of the output stream class (such as PrintStream, BufferedWriter, etc.). To use it, you can call the following method:

outputStream.flush();

Example of flush()

The following example shows how to use the flush() method:

import java.io.FileOutputStream;
import java.io.PrintStream;

public class FlushExample {

    public static void main(String[] args) {
        try {
            // 创建一个 PrintStream，将数据写入文件
            PrintStream out = new PrintStream(new FileOutputStream("output.txt"));

            // 向文件中写入一些数据
            out.println("Hello, world!");

            // 使用 flush() 方法将缓冲区中的数据写入文件
            out.flush();

            // 关闭 PrintStream
            out.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

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