Does Hashmap autosort?

Question

This is my hashmap :

HashMap hashMapTest = new HashMap();

and I insert Date.getTime() into this

Answer 1

No, HashMaps don't sort their keys automatically.

You want a TreeMap for sorting the keys, or a LinkedHashMap to retain the insertion order.

Here's an example:

long l0 = 0l;
long l1 = 1l;
Map hashMap = new HashMap();
Map treeMap = new TreeMap();
Map linkedHashMap = new LinkedHashMap();
// does not guarantee key order 1, 0
hashMap.put(l1, null);
hashMap.put(l0, null);
// guarantees key order 0, 1
treeMap.put(l1,  null);
treeMap.put(l0,  null);
// guarantees key order 1, 0
linkedHashMap.put(l1,  null);
linkedHashMap.put(l0,  null);
System.out.printf("HashMap: %s%nTreeMap: %s%nLinkedHashMap: %s%n", hashMap, treeMap, linkedHashMap);

Output

HashMap: {0=null, 1=null}
TreeMap: {0=null, 1=null}
LinkedHashMap: {1=null, 0=null}