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Some doubts about generics

Mahtab Alam
Ranch Hand

Joined: Mar 28, 2012
Posts: 354


A non generic class extending a generic class without passing the Type parameter to super class X
What i think is , it compiles because compiler sees it as class Y extends X<Object>
Am i right ?


Then why does this compile.

Looking for answer that i can understand , Oracle Java Programmer , Oracle SQL Expert , Oracle Java Web Component Developer
Himai Minh
Ranch Hand

Joined: Jul 29, 2012
Posts: 1032
Generic was not available until JDK 1.5.
For backward compatibility, it compiles when you use a generic class in a non-generic way.
For example,we are supposed to use HashMap in this way : HashMap<String, String> or any other type. But it compiles if you put HashMap h = new HashMap();
You will get a warning, but it compiles in JDK 6.
Mahtab Alam
Ranch Hand

Joined: Mar 28, 2012
Posts: 354

Thanks for reply
but this was of no help
Alexandre Leveille

Joined: Jan 26, 2013
Posts: 12

it compiles because compiler sees it as class Y extends X<Object>

No, it works to maintain backward compatibility.

You just created the classes S and V, but most of the time you'll have to deal with legacy code.

For example, last year you downloaded ms-util.jar from They had this awesome class S that did a lot of thing:

You decided on your project to extend that class to add some functionality:

Everything is fine, right? No generics so it is simple ;)

However, some Monday morning, a user reports a bug with your application. You investigate a bit and you find that the bug is in the class S... but you are in luck, it has been fixed in the latest version of ms-util.jar. So you head to and download the newest version of ms-util.jar.

When you open (and decompile) the new ms-util.jar, here's what you find:

Microsoft has changed their classes to use generics. Awesome.... but will it break your code? Remember, your class V that extends S does not use generics and even pass a non-typed list to their methods!!

Sun made it that your old code (class V) would continue to compile. If they hadn't, you would have needed to recode all your classes!
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