class Test3 {
public static void main(String args[]){
Map<Integer, String> aa = new HashMap();
System.out.println(aa.put(1, "test"));
}
}
whenever I execute this statement it prints null value. I want to know why it printing the null value. What is happening?
From the Javadoc of Map.put
:
V put(K key, V value)
...
Returns : the previous value associated with key, or null if there was no mapping for key.
The map is empty before the call to put
, so "there was no mapping for key", so null
is returned.
implementation of put is something like below
@Override
public V put(K key, V value) {
return putImpl(key, value);
}
If the map previously contained a mapping for the key, the old value is replaced. else null will return because there is no mapping.
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