Wildcard test program. - Java Object Oriented Design

Java examples for Object Oriented Design:Generic Method

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Description

Wildcard test program.

Demo Code

import java.util.ArrayList;

public class Main 
{
   public static void main(String[] args) 
   {/*  w  w w.j av a 2  s.  c  om*/

      Integer[] integers = {1, 2, 3, 4, 5};
      ArrayList<Integer> integerList = new ArrayList<>();

      // insert elements in integerList
      for (Integer element : integers)
         integerList.add(element);

      System.out.printf("integerList contains: %s%n", integerList);
      System.out.printf("Total of the elements in integerList: %.0f%n%n",
         sum(integerList));

      // create, initialize and output ArrayList of Doubles, then 
      // display total of the elements 
      Double[] doubles = {1.1, 3.3, 5.5};
      ArrayList<Double> doubleList = new ArrayList<>();

      // insert elements in doubleList
      for (Double element : doubles)
         doubleList.add(element);

      System.out.printf("doubleList contains: %s%n", doubleList);
      System.out.printf("Total of the elements in doubleList: %.1f%n%n", 
         sum(doubleList));

      // create, initialize and output ArrayList of Numbers containing 
      // both Integers and Doubles, then display total of the elements 
      Number[] numbers = {1, 2.4, 3, 4.1}; // Integers and Doubles
      ArrayList<Number> numberList = new ArrayList<>();

      // insert elements in numberList
      for (Number element : numbers)
         numberList.add(element);

      System.out.printf("numberList contains: %s%n", numberList);
      System.out.printf("Total of the elements in numberList: %.1f%n", 
         sum(numberList));
   } 

   // total the elements; using a wildcard in the ArrayList parameter
   public static double sum(ArrayList<? extends Number> list)
   {
      double total = 0; // initialize total

      // calculate sum
      for (Number element : list)
         total += element.doubleValue();

      return total;
   } 
}

Result


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