Java Generic Interface Examples

In this article, we will learn how to write a generic interface with examples.

The Generalized Syntax for a Generic Interface

interface interfaceName<type-param-list> { // ...
}
class className<type-param-list>
           implements interfaceName<type-param-list> {
     // ....
}
  • type-param-list is a comma-separated list of type parameters.
  • when a generic interface is implemented, you must specify the type arguments

Java Generic Interface Examples

Let's write a simple example to find the minimum and the maximum value of Integer, character and String array.
  1. Create three arrays - Integer, character and String array.
  2. Write generic methods to find the minimum and a maximum value of any type of array.
/**
 * Generic interface example to find min and max of array.
 * @author javaguides.net
 *
 */
public class GenericInterfaceExample {
    public static void main(String args[]) {
         Integer intOfArray[] = { 3, 6, 2, 8, 6 };
         Character charOfArray[] = { 'A', 'r', 'V', 'w' };
         String strOfArray[] = {"abc", "xyz", "pqr"};
  
         MinMaxImpl<Integer> intMinMax = new MinMaxImpl<Integer>(intOfArray);
         MinMaxImpl<Character> charMinMax = new MinMaxImpl<Character>(charOfArray);
         MinMaxImpl<String> strMinMax = new MinMaxImpl<String>(strOfArray);

         System.out.println("Max value in intOfArray: " + intMinMax.max());
         System.out.println("Min value in intOfArray: " + intMinMax.min());

         System.out.println("Max value in charOfArray: " + charMinMax.max());
         System.out.println("Min value in charOfArray: " + charMinMax.min());
  
         System.out.println("Max value in strOfArray: " + strMinMax.max());
         System.out.println("Min value in strOfArray: " + strMinMax.min());
     }
}

interface MinMax<T extends Comparable<T>> {
     T min();

     T max();
}

class MinMaxImpl<T extends Comparable<T>> implements MinMax<T> {
     T[] vals;

     MinMaxImpl(T[] o) {
         vals = o;
     }

     public T min() {
         T v = vals[0];

         for (int i = 1; i < vals.length; i++) {
             if (vals[i].compareTo(v) < 0) {
                  v = vals[i];
             }
         }

          return v;
     }

     public T max() {
          T v = vals[0];

          for (int i = 1; i < vals.length; i++) {
             if (vals[i].compareTo(v) > 0) {
                  v = vals[i];
             }
          }

          return v;
     }
}
Output:
Max value in intOfArray: 8
Min value in intOfArray: 2
Max value in charOfArray: w
Min value in charOfArray: A
Max value in strOfArray: xyz
Min value in strOfArray: abc

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