Java generic class syntax

Question

I know that I can create a class in java like this:

public class test {/*some code*/}

But now I have this:

public class coada < T extends Number & Comparable < Number>> {
    List <T> pq = new ArrayList <T>();

    public void add(T e , List <T> c) {
        c.add(e);
        Collections.sort(c);
    }

    public void remove(List < ? extends Number> c) {
        c.remove(0);
    }
}

I don't understand the more complicated syntax of the angled brackets and parameter lists.

I have these questions:

Can someone clarify the syntax used in the example?
I know Java doesn't support multiple inheritance. So how are Number & Comparable possible?
I thought generics are used for collections, not classes, so, how can class coada have a type parameter?

Recommended reading: The Java(tm) Tutorials: Lesson: Generics (Updated) — T.J. Crowder
– T.J. Crowder, Commented Apr 4, 2015 at 16:42
Do you see that Comparableis an interface and not a class? — eduyayo
– eduyayo, Commented Apr 4, 2015 at 16:44
edit your question and select code and press ctrl-M not use br — Tamil Selvan C
– Tamil Selvan C, Commented Apr 4, 2015 at 16:44
When posting questions, you don't use HTML tags, it is WYSIWYG style. — clearlight
– clearlight, Commented Apr 4, 2015 at 16:55

dbf · Accepted Answer · 2015-04-04 16:45:49Z

2

T extends Number & Comparable <Number> T extends Number and implements Comparable
Generics don't require type to be a collection.

answered Apr 4, 2015 at 16:45

dbf

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Comments

Eran · Accepted Answer · 2015-04-04 17:03:25Z

1

Comparable is an interface, so T can extend Number and implement Comparable<Number> (and any number of other interfaces) at the same time.

As for your second question, any class can have type parameters, not only Collections. coada < T extends Number & Comparable < Number>> means that the class coada has a type parameter called T which must be either Number or a sub-class of Number and implement the interface Comparable<Number>.

edited Apr 4, 2015 at 17:03

answered Apr 4, 2015 at 16:43

Eran

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2 Comments

MyUserQuestion Over a year ago

??? interfaces are implemented not extended so you still didn't explained the sintax extend Number & Comparable . that is what i asked... And also you didn't explained how class coada have a type parameter .... so what do you want to prove? i am a biginer . if you don't explain it clear just don't pls

Eran Over a year ago

@MyUserQuestion Sorry, I missed your second question and only answered the first one.

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