About Generic data type

Question

LinkedList<Integer> i=new LinkedList();
How is it compile properly ?

Answer 1

Mrjavan wrote:
No everything is run properly.Yes, but the compiler gives you a warning about the third line:
$ javac Foo.java
Note: Foo.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
$ javac -Xlint:unchecked Foo.java
Foo.java:8: warning: [unchecked] unchecked conversion
found   : java.util.HashMap
required: java.util.HashMap<java.lang.Integer,java.lang.String>
    HashMap<Integer,String>hmap3=new HashMap();
                                 ^
1 warning
$To summarize:
In the first line, you declare the full parameterized type in the instanciation, but discard it because your variable only has the raw type. So you're doing useless work.
In the second line you declare the full parameterized type in both the variable declaration and the instanciation. That's the correct way. Now the compiler can check access to hmap2 for type correctness.
In the third line you declare the full parameterized type in the variable declaration, but use a raw type for the instanciation. Here the compiler gives you a warning that it can't check the assignment at runtime. Don't do that.
Note that at runtime all 3 will behave exactly the same, because of type erasure (google that term).