在Java中打印时，错误输出流与标准输出流并发

Question

When this code gets executed, it produces scrambled outputs with no particular order between System.out.print() and System.err.print() . Why is that so?

for (int i = 0; i < 100; i++) {
    System.out.print(i+" ");
    System.err.print(i+"+");
}

Why is the standard error output stream is concurrent with standard output stream when printing in Java?

Answer 1

System.out and System.err are two different streams and so, they work at different times. The problem you're experiencing here is because in console applications both streams are flushed to the same output buffer, which is the console. Each stream can flush at different time, the console buffer will care about the synchronization for you, but this leads to unpredictable results.

If you want/need to have a single and better managed output for both streams, use a logger library like log4j2 or logback, that already solves these problems.