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Java

Posted by J Tan
J Tan
11,847 Points

Why does some Java declaration have object reference not match the object type?

For the following code, why does the variable use Map declaration instead of HashMap declaration? Would it be wrong to have the variable reference also be HashMap?

Map<Integer, String> mapExample = new HashMap<Integer, String>();

Vs

Scanner input = new Scanner(System.in);

When declaring objects, when would it be beneficial to have the variable type be different from the object type?

2 Answers

Martin Gallauner
Martin Gallauner
10,808 Points

Hi

You use the Map declaration because then you could use any subtype from Map. Maybe you want to change some stuff in the future.

Because I'm really bad at explaining, this link might help you

https://stackoverflow.com/questions/1348199/what-is-the-difference-between-the-hashmap-and-map-objects-in-java

james south
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
james south
Front End Web Development Techdegree Graduate 33,271 Points
james south
.a{fill-rule:evenodd;}techdegree seal-36
james south
Front End Web Development Techdegree Graduate 33,271 Points

scanner is a class and is used directly. map is an interface and is implemented with various classes, such as hashMap, treeMap, etc. the java docs list what classes can be used to implement the map interface.