Compilation error - generics

[Bryan Buchanan]

Maybe I'm missing something obvious, but why does this code:

public class FirstCodenameOneLibrary {

    /**
     * Method javadoc information
     */
    public void hello() {
        System.out.println("Hello");
    }

    public void addObjects(Map<Integer, Object> objects) {
        int maxObjNumber = Collections.max(objects.keySet());
    }
}

give this error:

Compiling 1 source file to /home/bryanb/NetBeansProjects/PDFjet/build/tmp
/home/bryanb/NetBeansProjects/PDFjet/src/com/codename1/hello/FirstCodenameOneLibrary.java:24: error: no suitable method found for max(Set<Integer>)
        int maxObjNumber = Collections.max(objects.keySet());
    method Collections.<T#1>max(Collection<? extends T#1>) is not applicable
      (inferred type does not conform to upper bound(s)
        inferred: Integer
        upper bound(s): Comparable<? super Integer>,Object)
    method Collections.<T#2>max(Collection<? extends T#2>,Comparator<? super T#2>) is not applicable
      (cannot infer type-variable(s) T#2
        (actual and formal argument lists differ in length))
  where T#1,T#2 are type-variables:
    T#1 extends Object,Comparable<? super T#1> declared in method <T#1>max(Collection<? extends T#1>)
    T#2 extends Object declared in method <T#2>max(Collection<? extends T#2>,Comparator<? super T#2>)
1 error

The Netbeans project is JDK8. The same code compiles fine with JavaSE. The method signatures for Collections.max() are the same for CN1 and regular Java.

[Steve Hannah]

Currently Integer doesn't implement Comparable.  Its on the to do list so hopefully we'll have this soon.  In the mean time, use the 2-arg version of Collections.max(Collection, Comparable), and pass it a comparable that can compare integers.

Steve

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Steve Hannah

Software Developer

Codename One

http://www.codenameone.com

[Bryan Buchanan]

OK - thanks Steve - I didn't think to look at Integer class.