Why is System.err.println is printed before then System.out.println?

Question

I was tryingout Logger example from wiki chain of responsibility article. running the example in idea it prints:

Sending to stderr: An error has occurred.
Writing to stdout: Entering function y.
Writing to stdout: Step1 completed.
Sending via email: Step1 completed.
Writing to stdout: An error has occurred.
Sending via email: An error has occurred.

but when i put a break point in stderrs writeMessage

class StderrLogger extends Logger {
    public StderrLogger(int mask) {
        this.mask = mask;
    }

    protected void writeMessage(String msg) {
        System.err.println("Sending to stderr: " + msg);//break out here
    }
}

it prints all the messags except std err, there is no threads involved here, then why its printing stderr at first line in run case?.

Answer 1

System.err flushes differently from System.out in Eclipse.

Try this in Eclipse:

public class Derp {
    public static void main(String[] args) {
        for(int i = 0; i < 10; i++) {
            System.out.println("OUT");
            System.err.println("ERR");
        }
    }
}

This will randomly print out most of the OUTs and most of the ERRs in big chunks. However, this is an Eclipse issue, not a Java issue, as pointed out by Evgeniy Dorofeev.

If you run this sample program in a terminal, you will notice the correct output, without any flushing needed.

Update: Thanks to Evgeniy Dorofeev for pointing this out! The flushing not working is an Eclipse problem!