FULL PRODUCT VERSION :
$ java -version
java version "1.8.0_161"
Java(TM) SE Runtime Environment (build 1.8.0_161-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.161-b12, mixed mode)



ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [版本 10.0.16299.192]

EXTRA RELEVANT SYSTEM CONFIGURATION :
JAVA_TOOL_OPTIONS: -Dfile.encoding=UTF8

A DESCRIPTION OF THE PROBLEM :
public static void main(String[] args) {
Calendar cal = Calendar.getInstance();
Date today = new Date(System.currentTimeMillis());
cal.setTime(today);
System.out.println(today);
int month = cal.get(Calendar.MONTH);
System.out.println(month);
}

Sun Feb 11 11:03:44 CST 2018
1

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
public static void main(String[] args) {
Calendar cal = Calendar.getInstance();
Date today = new Date(System.currentTimeMillis());
cal.setTime(today);
System.out.println(today);
int month = cal.get(Calendar.MONTH);
System.out.println(month);
}

Sun Feb 11 11:03:44 CST 2018
1


REPRODUCIBILITY :
This bug can be reproduced always.