How can I make this unchecked method invocation checked?

[Dillinger4]

This is driving me crazy. As it stands below the compiler complains that the method invocation is unchecked. If I add a type parameter getMax(Collection<Num> c) the compiler moans that it canno't find symbol method max(java.util.Collection<Num>).

public static Num getMax(Collection c){
 return Collections.max(c); 
}

The method prototype simply suggests that any type can be passed in that extends the type that the Collection is marked to hold.

public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll)

[CornedBee]

Yes, but Java's not smart enough to deduce the type, it seems. Try:

return Collections.max<Num>(c);

[Dillinger4]

This is very confusing. The type param <Num> is necessary within or else im playing with unchecked method calls,

public static Num getMax(Collection<Num> c){
 return Collections.max(c); 
}

but then the compiler seems to not be able to find a version of

max(java.util.Collections<Num>)

return Collections.max<Num>(c);

Simple dosen't work.

[CornedBee]

Does your Num class implement Comparable?

[Dillinger4]

Posted by CornedBee

Does your Num class implement Comparable?

Now it does. Thanks for the help.

import java.util.Set;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections; 

public class Max{
 public static void main(String[] args){
  Collection<Num> numl = new ArrayList<Num>(); 
  numl.add(new Num("2"));
  numl.add(new Num("6"));
  numl.add(new Num("3"));
  numl.add(new Num("1"));
  numl.add(new Num("5"));
  numl.add(new Num("4"));
  System.out.print("Max element is " + getMax(numl).getNum());   
 }
 public static Num getMax(Collection<Num> c){
   return Collections.max(c); 
 }
}
class Num implements Comparable<Num>{
 private String i; 
 public Num(String i){
  this.i = i; 
 }
 public int compareTo(Num num){
  int x = i.compareTo(num.i);
  return x; 
 }
 public String getNum(){
  return i; 
 }
}