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@techDeep It is constant time i.e. O(1). Basically for looking into the key value pair, HashMap uses hashing which gives the precise address location of the 'bucket' which contains the Key.
For example, hashFunction(key)= Memory Location, which you can see is not dependent on n.
PS : it is not as simple as it appears in the example, its just for the sake of simplicity, but the process is essentialy O(1).

@techieDeep
suppose your application needs several such objects(hundreds of thousands) , so for increasing the throughput of your application , instead of creating an object everytime , you can look into already existing objects table and assign an 'equal' object to it.
Precisely same is done in case of String class in java. Infact, it was the main reason to make String immutable.

This was the first answer I gave. But this implementation sucks , as it blocks all requesting threads that need only to fetch object reference. To make it efficient , solution has to be that we can get Singleton object reference anytime , since its a read only meahod.

private static SingletonObject obj;
SingletonObject getReference()
{
if (obj!=null)
return obj;
else
{
synchronized(this)
{
while(obj==null)
{
obj = new SingletonObject();
}
return obj;
}
}}

To be precise, they are reusable and de facto thread safe.

Yes , but instead creating a new Class for storing Date, we could use do that in our constructer itself.

// both name and date are marked final
immutable(String name,Date date)
{
 this.name = name;
// create own copy, initialize it for the date object given , could have used copy constructer if any.
this.date = new Date(date.getTime());
}