Using generics to make a swap method

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I'm having trouble with a basic concept in my book. I am supposed to make a method swap(); that swaps positions with first and second using generics. I believe my method is correct however I changed the code in the pair class from T,S to T because I was getting errors and thought that would solve the issue but this is not the case. My problem is that I now get a lot of compile time errors in my demo class and I cannot find a solution.

public class Pair<T>
    {
       private T first;
       private T second;



   public Pair(T firstElement, T secondElement)
   {
      first = firstElement;
      second = secondElement;
   }


   public T getFirst() { return first; }

   public T getSecond() { return second; }

  public void swap()
  {

   T temp = first;
    first = second;
    second = temp;
  }

   public String toString() { return "(" + first + ", " + second + ")"; }
}

This is the compile time error that I am getting.

PairDemo.java:23: error: wrong number of type arguments; required 1
   public static Pair<String, Integer> firstContaining(
                     ^
PairDemo.java:6: error: wrong number of type arguments; required 1
      Pair<String, Integer> result = firstContaining(names, "a");
          ^
PairDemo.java:11: error: cannot find symbol
      swap();
      ^
  symbol:   method swap()
  location: class PairDemo
PairDemo.java:30: error: wrong number of type arguments; required 1
            return new Pair<String, Integer>(strings[i], i);
                           ^
PairDemo.java:33: error: wrong number of type arguments; required 1
      return new Pair<String, Integer>(null, -1);

This is my demo class

public class PairDemo
{
   public static void main(String[] args)
   {
      String[] names = { "Tom", "Diana", "Harry" };
      Pair<String, Integer> result = firstContaining(names, "a");
      System.out.println(result.getFirst());
      System.out.println("Expected: Diana");
      System.out.println(result.getSecond());
      System.out.println("Expected: 1");
      swap();
   }


   public static Pair<String, Integer> firstContaining(
      String[] strings, String sub)
   {
      for (int i = 0; i < strings.length; i++)
      {
         if (strings[i].contains(sub))
         {
            return new Pair<String, Integer>(strings[i], i);
         }
      }
      return new Pair<String, Integer>(null, -1);
   }
}

asked 23 secs ago

sippycup

3

Using generics to make a swap method