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In C# you can initialize Hashtables (and many other types of objects) using code like this -
Hashtable table = new Hashtable {{1, 1}, {2, 2}};
Is there anything like this in Java or do you have to just declare the Hashtable first and then manually put items in it one by one?
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A Hashtable is an array of a list. Each list is known as a bucket. The position of the bucket is identified by calling the hashcode() method. A Hashtable contains values based on the key. Java Hashtable class contains unique elements.
put() method of Hashtable is used to insert a mapping into a table. This means we can insert a specific key and the value it is mapping to into a particular table. If an existing key is passed then the previous value gets replaced by the new value. If a new pair is passed, then the pair gets inserted as a whole.
Hashtable methods are synchronized, but that only provides method-level protection against race conditions. (So a Hashtable —unlike a HashMap —will not become internally corrupted if multiple threads are concurrently trying to modify the data.) It is only in this sense that Hashtable is thread-safe.
This is answered elsewhere but you can use an anonymous subclass:
new HashMap<Integer, Integer>() {{ put(1, 1); put(2, 2); }};
Lot's of boiler plate, but still a one-liner :). This will, unfortunately, also complain about the missing serialVersionUID constant which you can either add or ignore the warning on.
This is called an instance initializer block, more information here.
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