I have this String to String map, and I am trying to pass char as a key
Map<String, String> phone = new HashMap<String, String>() {{
put("2", "abc");
put("3", "def");
put("4", "ghi");
put("5", "jkl");
put("6", "mno");
put("7", "pqrs");
put("8", "tuv");
put("9", "wxyz");
}};
String letterList = phone.get('2'); //null
String letterList = phone.get(String.valueOf('2')); //it works
Why does the first case not work? In my understanding, char can be implicitly converted to String "2", and HashMap use equals() to compare keys, so that it should retrieve the key in map?
Why does the first case not work? In my understanding, char can be implicitly converted to String "2"
Your understanding is incorrect. A char will not be implicitly converted to String. If you look at the documentation, you will see this method get(Object key). I don't know why this isn't get(K key) instead. However, this explains why your first example compiles without any errors: the char constant is autoboxed into a Character object. Since the Character with the value '2' is not a key in your Map, get() returns null.