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My System.out.println() and System.err.println() calls aren't being printed to the console in the order I make them.
public static void main(String[] args) { for (int i = 0; i < 5; i++) { System.out.println("out"); System.err.println("err"); } } This produces:
out out out out out err err err err err Instead of alternating out and err. Why is this?
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System. out is "standard output" (stdout) and System. err is "error output" (stderr). Along with System.in (stdin), these are the three standard I/O streams in the Unix model.
out is "standard output" (stdout) and System. err is "error output" (stderr). If you are using a simple Java console application, both outputs will be the same (the command line or console) but you can reconfigure the streams so that for example, System. out still prints to the console but System.
The key difference between them is that printf() prints the formatted String into console much like System. out. println() but the format() method returns a formatted string, which you can store or use the way you want.
They are different streams and are flushed at different times.
If you put
System.out.flush(); System.err.flush(); inside your loop, it will work as expected.
To clarify, output streams are cached so all the write goes into this memory buffer. After a period of quiet, they are actually written out.
You write to two buffers, then after a period of inactivity they both are flushed (one after the other).
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