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Brendan Whiting
Front End Web Development Techdegree Graduate 84,738 PointsHelp understanding why we create an instance with an interface this way
I'm seeing this kind of pattern a few times in the Java courses:
Map<String,String> myMap = new HashMap<String, String>();
Why do we call it Map on the left and HashMap on the right? Why the difference?
Thx
2 Answers
Daniel Vigil
26,473 PointsThere are two sides to the equation. On the left you are referencing the Map interface and on the right you are declaring the concrete child classes of Map. It does open your code to more flexibility in the declaration throughout your code.
Florian Tönjes
Full Stack JavaScript Techdegree Graduate 50,856 PointsHey Brendan Whiting,
I think it gives you more flexibility. You can later assign a Treemap to myMap for example.
Alexander Nikiforov
Java Web Development Techdegree Graduate 22,175 PointsAlexander Nikiforov
Java Web Development Techdegree Graduate 22,175 PointsThere are number if discussions about that in the web. Checkout for example this Stack nice discussion:
http://stackoverflow.com/questions/9852831/polymorphism-why-use-list-list-new-arraylist-instead-of-arraylist-list-n