java - What is the difference between raw types and generic types in this declaration -

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• what raw type , why shouldn't use it? 12 answers

what difference between raw types , generic types in declaration

list<integer> list1 = new arraylist<>();  list<integer> list2 = new arraylist(); 

for these declaration can't do

list1.add("hello"); list2.add("hello"); 

so difference

on other word benefit of angle brackets in first declaration

when arraylist<>(), type in angle brackets inferred declaration, resolves arraylist<integer> @ compile time.

if omit angle brackets, assignment uses raw type, i.e. collection type without information of element type. no type inference done compiler assignment.

both lines not compile:

list1.add("hello") list2.add("hello") 

because both list1 , list2 variables declared arraylist<string>.

the point of specifying <> assignment of arraylist() arraylist<string> should generate compiler warning of unchecked assignment, because compiler can't verify raw typed collection right of = sign contains integers. in simple case such yours, can control correctness of code visually. consider more complex scenario:

arraylist rawlist = new arraylist(); rawlist.add("one");  arraylist<integer> list = rawlist; 

here break generic system assigning raw list contains string typed list variable should contain integers. that's compiler warning of unchecked assignment comes in handy.