Type Inference means determining the Type by compiler at compile-time.
It is not new feature in Java SE 8. It is available in Java 7 and before Java 7 too.
Before Java 7:-
Let us explore Java arrays. Define a String of Array with values as shown below:
String str[] = { "Java 7", "Java 8", "Java 9" };
Here we have assigned some String values at right side, but not defined it’s type. Java Compiler automatically infers it’s type and creates a String of Array.
Java 7:-
Oracle Corporation has introduced “Diamond Operator” new feature in Java SE 7 to avoid unnecessary Type definition in Generics.
Map<String,List<Customer>> customerInfoByCity = new HashMap<>();
Here we have not defined Type information at right side, simply defined Java SE 7’s Diamond Operator “”.
Java SE 8:-
Oracle Corporation has enhanced this Type Inference concept a lot in Java SE 8. We use this concept to define Lambda Expressions, Functions, Method References etc.
ToIntBiFunction<Integer,Integer> add = (a,b) -> a + b;
Here Java Compiler observes the type definition available at left-side and determines the type of Lambda Expression parameters a and b as Integers.
