How do I make Java Hashtable.containsKey to work for Array?

Question

Sorry to ask this question but i am new to Java.

Hashtable<byte[],byte[]> map = new Hashtable<byte[],byte[]>();
byte[] temp = {1, -1, 0};
map.put(temp, temp);
byte[] temp2 = {1, -1, 0};;
System.err.println(map.containsKey(temp2));

does NOT work with .containsKey (as the printed result is "False")

Hashtable<Integer,Integer> mapint = new Hashtable<Integer, Integer>();
int i = 5;
mapint.put(i, i);
int j = 5;
System.err.println(mapint.containsKey(j));

works (the printed result is "True")

I understand it has something to do with object reference, but could not reach any solution after searching...

Is there anyway I can use Hashtable to find key with Array type? I just want to test if a specific array is in Hashtable as a key...

Any hits would be great. Thank!!!

Answer 1

You can't use arrays as keys in a HashTable/HashMap, since they don't override the default implementation of Object's equals, which means temp.equals(temp2) if and only if temp==temp2, which is not true in your case.

You can use a Set<Byte> or List<Byte> instead of a byte[] for your key.

For example :

Hashtable<List<Byte>,Byte[]> map = new Hashtable<List<Byte>,Byte[]>();
Byte[] temp = {1, -1, 0};
map.put(Arrays.asList(temp), temp);
Byte[] temp2 = {1, -1, 0};;
System.err.println(map.containsKey(Arrays.asList(temp2)));