Calendar.equals throws an IllegalArgumentException if a non-lenient Calendar object is involved. The following is a test case.

--
import java.util.*;

public class CalEq {
    public static void main(String[] args) {
        Calendar cal = Calendar.getInstance();
        cal.setLenient(false);
        cal.set(cal.MONTH, 100);
        System.out.println(Calendar.getInstance().equals(cal));
    }
}

--
Exception in thread "main" java.lang.IllegalArgumentException
         at java.util.GregorianCalendar.computeTime(GregorianCalendar.java:1504)
         at java.util.Calendar.updateTime(Calendar.java:1544)
         at java.util.Calendar.getTimeInMillis(Calendar.java:912)
         at java.util.Calendar.equals(Calendar.java:1114)
         at java.util.GregorianCalendar.equals(GregorianCalendar.java:510)
         at CalEq.main(CalEq.java:8)

###@###.### 2002-07-30