Is Run time Exception or null or Key Not Found Exception?

HashMap hashMap = new HashMap() ;
   hashMap.put("Matched", 1000L) ;  
   System.out.println("Map value" + hashMap.get("Unmatched")) ;


Output:  null.

get

public V get(Object key)

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.More formally, if this map contains a mapping from a key k to a value v such that (key==null ? k==null : key.equals(k)), then this method returns v; otherwise it returns null. (There can be at most one such mapping.)
A return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.

Specified by:

get in interface Map<K,V>

Overrides:

get in class AbstractMap<K,V>

Parameters:

key - the key whose associated value is to be returned

Returns:

the value to which the specified key is mapped, or null if this map contains no mapping for the key

See Also:

put(Object, Object)