compilation warnings

[AshutoshP Patil]

hi ,
1)can anybody please explain me why it gives a warning while compilation?
2)what should be done to avoid this warning?
3)in which all conditions compilation warnings gives in generics ?

the below code is compiled in j2se 1.6 environment.

thanks in advance

  import java.util.*;
 class ABICOMP implements Comparator{
      public int compare(Object ob1, Object ob2){
           return 1;
      }
      public String toString(){
           return "W";
      }
 }
 
 public class TMapcomp{
      public static void main(String argv[]){
           Set<ABICOMP> cs=new TreeSet<ABICOMP>(new ABICOMP());
           cs.add(new ABICOMP());
           cs.add(new ABICOMP());
           cs.add(new ABICOMP());
           for(ABICOMP a:cs)
                System.out.print(a+",");
      }
 }  

[Manish Singh]

1) Warning because that is not an error but may cause problems.
2) Those warning should be removed as far as possible.
3) For generics warnings comes when you use a parametrized thing(class,interface , method) without specifying the parameter like you have done for the Comparator.

The best way to handle warnings is to use an IDE like eclipse. It will suggest you how you can remove those warnings.

[Rob Spoor]

Comparator is generic - it should be Comparator<ABICOMP>.

Instead of making ABICOMP implement Comparator<ABICOMP> (meaning one instance can compare any two other instances), you should consider implementing Comparable<ABICOMP> instead. This allows each ABICOMP instance to compare itself to any other instance. You will then no longer need to create an instance just to use as the Comparator. The tree set can be created as "new TreeSet<ABICOMP>()" and will let each element compare itself to the other elements.

[AshutoshP Patil]

thanks all.

i tried with implementing implement Comparable <ABICOMP> it worked fine (no warnings).But,implementing Comparator<ABICOMP> does not work out ..

[Jesper de Jong]

AshutoshP Patil wrote:But,implementing Comparator<ABICOMP> does not work out ..

If you want more help with that, then please explain exactly what you mean - TellTheDetails.

[AshutoshP Patil]

i want to sort the objects of my class ABICOMP and ptint myclass objects by toString() method
by two ways such that no warnings should be there
1)one using comparator
2)second using comparable

[Michael Angstadt]

AshutoshP Patil wrote:thanks all.

i tried with implementing implement Comparable <ABICOMP> it worked fine (no warnings).But,implementing Comparator<ABICOMP> does not work out ..

Comparable is the right interface to use in your situation. Comparable is used on the classes that are being sorted.

Comparator is used if you want Java to ignore the rules that Comparable defines (or if the class does not implement Comparable). For example:

 public class TMapcomp{  
      public static void main(String argv[]){  
           Set<ABICOMP> cs=new TreeSet<ABICOMP>(new Comparator<ABICOMP>(){
                  @Override
                  public int compare(ABICOMP o1, ABICOMP o2) {
                        //the code in ABICOMP.compareTo() is ignored
                        return 0;
                  }
           });  
           cs.add(new ABICOMP());  
           cs.add(new ABICOMP());  
           cs.add(new ABICOMP());  
           for(ABICOMP a:cs)  
                System.out.print(a+",");  
      }  
 }

[AshutoshP Patil]

thanks michael
i got it .