Streams on Arrays in Java 8


Stream method of array class introduced in Java 8. Let us see an example wherein we are counting empty strings, eliminating empty strings, getting a list of square of distinct numbers, displaying random numbers, etc −

Example

import java.util.ArrayList;
import java.util.Arrays;
import java.util.IntSummaryStatistics;
import java.util.List;
import java.util.Random;
import java.util.stream.Collectors;
import java.util.Map;
public class Java8Tester {
   public static void main(String args[]) {
      System.out.println("Using Java 7: ");
      // Count empty strings
      List<String> strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl");
      System.out.println("List: " +strings);
      long count = getCountEmptyStringUsingJava7(strings);
      System.out.println("Empty Strings: " + count);
      count = getCountLength3UsingJava7(strings);
      System.out.println("Strings of length 3: " + count);
      //Eliminate empty string
      List<String> filtered = deleteEmptyStringsUsingJava7(strings);
      System.out.println("Filtered List: " + filtered);
      //Eliminate empty string and join using comma.
      String mergedString = getMergedStringUsingJava7(strings,", ");
      System.out.println("Merged String: " + mergedString);
      List<Integer> numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5);
      //get list of square of distinct numbers
      List<Integer> squaresList = getSquares(numbers);
      System.out.println("Squares List: " + squaresList);
      List<Integer> integers = Arrays.asList(1,2,13,4,15,6,17,8,19);
      System.out.println("List: " +integers);
      System.out.println("Highest number in List : " + getMax(integers));
      System.out.println("Lowest number in List : " + getMin(integers));
      System.out.println("Sum of all numbers : " + getSum(integers));
      System.out.println("Average of all numbers : " + getAverage(integers));
      System.out.println("Random Numbers: ");
      //print ten random numbers
      Random random = new Random();
      for(int i = 0; i < 10; i++) {
         System.out.println(random.nextInt());
      }
      System.out.println("Using Java 8: ");
      System.out.println("List: " +strings);
      count = strings.stream().filter(string->string.isEmpty()).count();
      System.out.println("Empty Strings: " + count);
      count = strings.stream().filter(string -> string.length() == 3).count();
      System.out.println("Strings of length 3: " + count);
      filtered = strings.stream().filter(string ->!string.isEmpty()).collect(Collectors.toList());
      System.out.println("Filtered List: " + filtered);
      mergedString = strings.stream().filter(string ->!string.isEmpty()).collect(Collectors.joining(", "));
      System.out.println("Merged String: " + mergedString);
      squaresList = numbers.stream().map( i ->i*i).distinct().collect(Collectors.toList());
      System.out.println("Squares List: " + squaresList);
      System.out.println("List: " +integers);
      IntSummaryStatistics stats = integers.stream().mapToInt((x) ->x).summaryStatistics();
      System.out.println("Highest number in List : " + stats.getMax());
      System.out.println("Lowest number in List : " + stats.getMin());
      System.out.println("Sum of all numbers : " + stats.getSum());
      System.out.println("Average of all numbers : " + stats.getAverage());
      System.out.println("Random Numbers: ");
      random.ints().limit(10).sorted().forEach(System.out::println);
      //parallel processing
      count = strings.parallelStream().filter(string -> string.isEmpty()).count();
      System.out.println("Empty Strings: " + count);
   }
   private static int getCountEmptyStringUsingJava7(List<String> strings) {
      int count = 0;
      for(String string: strings) {
         if(string.isEmpty()) {
            count++;
         }
      }
      return count;
   }
   private static int getCountLength3UsingJava7(List<String> strings) {
      int count = 0;
      for(String string: strings) {
         if(string.length() == 3) {
            count++;
         }
      }
      return count;
   }
   private static List<String> deleteEmptyStringsUsingJava7(List<String> strings) {
      List<String> filteredList = new ArrayList<String>();
      for(String string: strings) {
         if(!string.isEmpty()) {
            filteredList.add(string);
         }
      }
      return filteredList;
   }
   private static String getMergedStringUsingJava7(List<String> strings, String separator) {
      StringBuilder stringBuilder = new StringBuilder();
      for(String string: strings) {
         if(!string.isEmpty()) {
            stringBuilder.append(string);
            stringBuilder.append(separator);
         }
      }
      String mergedString = stringBuilder.toString();
      return mergedString.substring(0, mergedString.length()-2);
   }
   private static List<Integer> getSquares(List<Integer> numbers) {
      List<Integer> squaresList = new ArrayList<Integer>();
      for(Integer number: numbers) {
         Integer square = new Integer(number.intValue() * number.intValue());
           if(!squaresList.contains(square)) {
            squaresList.add(square);
         }
      }
      return squaresList;
   }
   private static int getMax(List<Integer> numbers) {
      int max = numbers.get(0);
      for(int i = 1;i < numbers.size();i++) {
         Integer number = numbers.get(i);
         if(number.intValue() > max) {
            max = number.intValue();
         }
      }
      return max;
   }
   private static int getMin(List<Integer> numbers) {
      int min = numbers.get(0);
      for(int i= 1;i < numbers.size();i++) {
         Integer number = numbers.get(i);
         if(number.intValue() < min) {
            min = number.intValue();
         }
      }
      return min;
   }
   private static int getSum(List numbers) {
      int sum = (int)(numbers.get(0));
      for(int i = 1;i < numbers.size();i++) {
         sum += (int)numbers.get(i);
      }
      return sum;
   }
   private static int getAverage(List<Integer> numbers) {
      return getSum(numbers) / numbers.size();
   }
}

Output

Using Java 7:
List: [abc, , bc, efg, abcd, , jkl]
Empty Strings: 2
Strings of length 3: 3
Filtered List: [abc, bc, efg, abcd, jkl]
Merged String: abc, bc, efg, abcd, jkl
Squares List: [9, 4, 49, 25]
List: [1, 2, 13, 4, 15, 6, 17, 8, 19]
Highest number in List : 19
Lowest number in List : 1
Sum of all numbers : 85
Average of all numbers : 9
Random Numbers:
-1329259351
-1288502777
1052219589
-436010315
2032772959
-1074471379
383859121
2080637483
952217347
1191784850
Using Java 8:
List: [abc, , bc, efg, abcd, , jkl]
Empty Strings: 2
Strings of length 3: 3
Filtered List: [abc, bc, efg, abcd, jkl]
Merged String: abc, bc, efg, abcd, jkl
Squares List: [9, 4, 49, 25]
List: [1, 2, 13, 4, 15, 6, 17, 8, 19]
Highest number in List : 19
Lowest number in List : 1
Sum of all numbers : 85
Average of all numbers : 9.444444444444445
Random Numbers:
-1389928981
-709249574
-677807422
-512038108
-338630337
61660472
537839354
1087935964
1453209077
1498898002
Empty Strings: 2
raja
Published on 25-Sep-2019 09:10:09
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