Question

I have some generics in the following code:

public <T extends Comparable<T>> int insertionSort(T[] a) {
   // throw new RuntimeException("not implemented");
      final int L = a.length;
      int compares = 0;
      
      for(int i = 1; i < L; i++){
          for(int j = i; j > 0 && a[j].compareTo(a[j - 1]) < 0; j--){
              
              Comparable tmp = a[j];   // PROBLEM HERE
              a[j] = a[j - 1];
              a[j - 1] = tmp;       // PROBLEM HERE
              
              compares++;
          }
      }
      
    return compares;
  }

// PROBLEM HERE – those two lines in the code have a fault.

The errors are I can’t make the assignments.

Answer 1

Your problem is that Comparable is an interface, not a class. you need to create an Object of a class that implements Comparable.

If T implements Comparable, than you can declare tmp as a T and use that:

 T tmp = a[j];
 a[j] = a[j - 1];
 a[j - 1] = tmp;