Java HashMap initialization?

Question

I already know how to initialize Java HashMap by using one of the following 2 ways

// way 1: apply generic type saftey
HashMap<String, Integer> hashMap1 = new HashMap<String, Integer>();

// way 2: general without apply generic type saftey
HashMap<String, Integer> hashMap2 = new HashMap();

My problem
What is the best practice

According to Eclipse Marker

Type safety: The expression of type HashMap needs unchecked conversion to conform to HashMap

So Its recommend to use

new HashMap<String, Integer>();

But according to Sonar Linter

Replace the type specification in this constructor call with the diamond operator ("<>").

So Its recommend to use

new HashMap();

Which one is the best? Why?

Related question https://stackoverflow.com/questions/507602/how-can-i-initialise-a-static-map — Ahmed Nabil, Dec 20 '18 at 08:42
Related question https://stackoverflow.com/questions/6802483/how-to-directly-initialize-a-hashmap-in-a-literal-way — Ahmed Nabil, Dec 20 '18 at 08:43
`new HashMap();` is not using the diamond operator. It should be `new HashMap<>();` — Eran, Dec 20 '18 at 08:43
new HashMap(); java 5 or 6 , New hashmap<>(); Java 7 onwards — Vishwa Ratna, Dec 20 '18 at 09:07

score 5 · Accepted Answer · answered Dec 20 '18 at 08:52

5

Use the Java 7 diamond operator:

HashMap<String, Integer> hashMap2 = new HashMap<>();

Diamond <> allows the compiler to infer types implicitly

See: Type Inference for Generic Instance Creation

answered Dec 20 '18 at 08:52

Anton Hlinisty

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Java HashMap initialization?

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