CODEWITHSUNDEEP
javagenerics
Ben
Ben

Reputation: 97

Need some slight help on this generic Java

I'm trying to make this code as generic as possible, but im stuck right on the last part. This is where my code is called:

List<Integer> NewList = map(OriginalList, new IFunction<Integer>(){         
      public <T extends Number> int execute(T anInt){ 
          return anInt.intValue() + 1;                  
      }     
});

then I have the method map:

public static <T> List<Integer> map(List<T> c, IFunction<T> f) {     
    List<Integer> TempList = new ArrayList<Integer>();
    for (T o : c){         
        TempList.add(f.execute(o));
    } 
    return TempList;
}

and the interface IFunction:

public interface IFunction<T> {     
    public <T extends Number> int execute(T o); 
}

my error is in Map() where it says TempList.add(f.execute(o)); i am trying to declare the TempList to be of type T and the execute method to return an incremented number in Type T.

Every time i fix one part of the code i seem to have ruined another part. Ideally all parameters would be generic and there would be no 'Integer' anywhere except where i call my code

Upvotes: 1

Views: 117

Answers (4)

Highland Mark
Highland Mark

Reputation: 1010

This is as close as I could get to removing Integer (changing variable names to start lower case):

public class Main
{
    public static void main(String[] args)
    {
        List<Integer> originalList = new ArrayList<Integer>();
        originalList.add(1);
        originalList.add(2);
        originalList.add(3);
        originalList.add(4);

        List<Integer> newList = map(originalList, new IFunction<Integer>()
        {
            public <T extends Number> T execute(T aNumber)
            {
                Integer result = aNumber.intValue() + 1;
                return (T) result;
            }
        });
        System.out.println(newList);
    }

    public static <T extends Number> List<T> map(List<T> c, IFunction<T> f)
    {
        List<T> tempList = new ArrayList<T>();
        for (T number : c)
        {
            tempList.add(f.execute(number));
        }
        return tempList;
    }

}

and

public interface IFunction<T> {
    public <T extends Number> T execute(T o);
}

Still got one inside the implementation of execute().

Upvotes: 0

Leo Izen
Leo Izen

Reputation: 4289

You should try a different Generic Setup:

public interface IFunction<T extends Number> {
    public int execute(T o); 
}

List<Integer> NewList = map(OriginalList, new IFunction<Integer>(){         
    public int execute(Integer anInt){ 
        return anInt.intValue() + 1;                  
    }     
});

public static <T extends Number> List<Integer> map(List<? extends T> c, IFunction<T> f) {     
    List<Integer> tempList = new ArrayList<Integer>();
    for (T o : c){         
        tempList.add(f.execute(o));
    } 
    return tempList;
}

Upvotes: 0

Claude
Claude

Reputation: 453

Try this:

IFunction.java

public interface IFunction <T extends Number> {
    T execute(T obj);
}

Main.java

public class Main {

    public static void main(String[] args) {
        List<Integer> originalList = new ArrayList<Integer>();
        List<Integer> newList = map(originalList, new IFunction<Integer>(){         
            public Integer execute(Integer anInt){ 
                return anInt.intValue() + 1;                  
            }     
        });
    }

    public static <T extends Number> List<T> map(List<T> c, IFunction<T> f) {     
        List<T> tempList = new ArrayList<T>();
        for (T o : c){         
            tempList.add(f.execute(o));
        } 
        return tempList;
    } 
}

Upvotes: 0

biziclop
biziclop

Reputation: 49754

You need to constrain your parameter in the map() method:

public static <T extends Number> List<Integer> map(List<T> c, IFunction<T> f) {     
  ...

Otherwise f.execute() will complain that the type of the argument can be anything, and it expects a Number.

Upvotes: 1

Related Questions