Difference in List l = new ArrayList() and List l = new ArrayList()

Question

What is difference in following two declarations

List<Integer> l = new ArrayList(); //and 

List<Integer> l = new ArrayList<Integer>();

If not then why in java 7 dimond operator ie <> is introduced to avoid type writing at right side of '=' or at object creation side.

Dublicate question : http://stackoverflow.com/questions/4166966/what-is-the-point-of-the-diamond-operator-in-java-7 — Murali, Dec 16 '13 at 05:39
@nbroos What you are describing is the type argument on the variable type declaration, not on the constructor. — Sotirios Delimanolis, Dec 16 '13 at 05:41

score 4 · Accepted Answer · answered Dec 16 '13 at 05:38

Consider this example

List<Float> f = new ArrayList();     // this list hold(s) Float(s).
f.add(2.0f);
List<Integer> l = new ArrayList(f);  // Oh no.... 
l.add(1);
System.out.println(l);

If I run the above I get

[2.0, 1]

If I used the diamond operator, I would get a compiler error. Does that help? At run-time every Collection holds java.lang.Ojbect(s) due to type erasure, this is compile time type checking only.

score 2 · Answer 2 · edited May 23 '17 at 10:25

2

This will causes the [unchecked] warning:

List<Integer> l = new ArrayList();

refer here

edited May 23 '17 at 10:25

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answered Dec 16 '13 at 05:40

Nambi

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ohh..my netbeans not showing that warning.How to do setting in netbeans to enable to show warnings – Prashant Shilimkar Dec 16 '13 at 05:43
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go to Tools > Options > Editor > Hints select java under there is .. – Nambi Dec 16 '13 at 05:45

Difference in List l = new ArrayList() and List l = new ArrayList()

2 Answers2

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