ADDITIONAL SYSTEM INFORMATION :
Does not depend on OS.

A DESCRIPTION OF THE PROBLEM :
Since in IO the reader is statically initialized, if System.setIn is called after the first read, it has no effect.

In some test it's useful to be able to re-set System.in, but if it is then read with IO.read the System.setIn has no effect.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Use the provided code


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
RUN 0
Read: Run 0
Read: hello world
Read: second line
RUN 1
Read: Run 1
Read: hello world
Read: second line
RUN 2
Read: Run 2
Read: hello world
Read: second line
RUN 3
Read: Run 3
Read: hello world
Read: second line
RUN 4
Read: Run 4
Read: hello world
Read: second line
RUN 5
Read: Run 5
Read: hello world
Read: second line
ACTUAL -
RUN 0
Read: Run 0
Read: hello world
Read: second line
RUN 1
RUN 2
RUN 3
Read: Run 3
Read: hello world
Read: second line
RUN 4
Read: Run 4
Read: hello world
Read: second line
RUN 5
Read: Run 5
Read: hello world
Read: second line

---------- BEGIN SOURCE ----------
import java.io.ByteArrayInputStream;
import java.nio.charset.StandardCharsets;
import java.util.Scanner;

public class ReproIO {
  public static void main(String[] args) {
    for (int run = 0; run < 3; run++ ) {
      String simulated = "Run " + run + "\nhello world\nsecond line\n";
      System.out.println("RUN " + run);
      ByteArrayInputStream bais = new ByteArrayInputStream(simulated.getBytes(StandardCharsets.UTF_8));
      System.setIn(bais);
      String line;
      while ((line = IO.readln()) != null)
        IO.println("Read: " + line);
    }
    for (int run = 3; run < 6; run++ ) {
      String simulated = "Run " + run + "\nhello world\nsecond line\n";
      System.out.println("RUN " + run);
      ByteArrayInputStream bais = new ByteArrayInputStream(simulated.getBytes(StandardCharsets.UTF_8));
      System.setIn(bais);
      Scanner s = new Scanner(System.in);
      while (s.hasNextLine())
        IO.println("Read: " + s.nextLine());
    }
  }
}
---------- END SOURCE ----------