comparing Dates in java when used as keys in HashMap

date, hashmap, java

Solution

You're comparing a `Date` object with a `String` one.

Iterator<Date> iterator = datesAndInts.keySet().iterator();  
while (iterator.hasNext()) {  
    Date key = iterator.next();
    System.out.println("comparing " + testDate + "with " + key + " result is " + testDate.equals(key)); 
    // this call to equals() returns true now.
}

Problem

I was trying to use a HashMap with `java.util.Date` as keys, but I came across this odd issue. When doing the below, I'm printing false. ``` Date testDate = new Date(timeInLongFormat); HashMap<Date,Integer> datesAndInts; datesAndInts.put(testDate, 0); Iterator iterator = datesAndInts.keySet().iterator(); while (iterator.hasNext()) { String key = iterator.next().toString(); System.out.println("comparing " + testDate + "with " + key + " result is " + testDate.equals(key)); // this call to equals() returns false. Integer testInt = datesList.get(key); // testInt is null, since the Date key cannot be found ... } ``` I would have expected the Date inserted as key and the Date returned by keySet to be identical, but they are not. Is that a normal behaviour ? Why ? Should I implement my own subclass of Date only comparing the time or something ?

Original source