Java 8 — Streams | Code Factory

Code Factory

4 min readMay 11, 2020

Index Page : Link
Reference Link : Link
Donate : Link

Introduction to Stream :

Difference between Collection & Stream

Collection is a group of objects as a single entity.
To process objects from the collection we should go for Stream.

Methods of Stream : filter() and map() :

filter() method :

package com.codeFactory.stream;import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;public class Test {
 public static void main(String... args) {
  ArrayList<Integer> i = new ArrayList<>();
  i.add(0);
  i.add(10);
  i.add(20);
  i.add(5);
  i.add(15);
  i.add(25);
  
  // without stream (until 1.7v)
  List<Integer> i1 = new ArrayList<>();
  for(Integer x : i) {
   if(x%2 == 0) {
    i1.add(x);
   }
  }
  System.out.println(i1);
  
  // with stream (1.8v onwords)
  List<Integer> i2 = i.stream().filter(x -> x%2 == 0).collect(Collectors.toList());
  System.out.println(i2);
 }
}

Output :

[0, 10, 20]
[0, 10, 20]

map() method :

package com.codeFactory.stream;import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;public class Test {
 public static void main(String... args) {
  ArrayList<Integer> i = new ArrayList<>();
  i.add(0);
  i.add(10);
  i.add(20);
  i.add(5);
  i.add(15);
  i.add(25);
  
  // without stream (until 1.7v)
  List<Integer> i1 = new ArrayList<>();
  for(Integer x : i) {
   i1.add(x * 3);
  }
  System.out.println(i1);
  
  // with stream (1.8v onwords)
  List<Integer> i2 = i.stream().map(x -> x * 3).collect(Collectors.toList());
  System.out.println(i2);
 }
}

Output :

[0, 30, 60, 15, 45, 75]
[0, 30, 60, 15, 45, 75]

Differnce between filter() and map() :

Filtering

If we want to filter elements from the collection based on some boolean condition, then we should go for filtering.
We can configure filter by using filter() method of stream interface.

Stream<T> filter(Predicate<? super T> predicate)argument can be boolean valued function or Lambda Expression
e.g. Stream s = c.stream().filter(i -> i%2 == 0);

Mapping

If we want to create a seperate new object for every object present in the Collection based on some function then we should go for mapping mechanism.
We can implement mapping by using map() method of stream interface.

<R> Stream<R> map(Function<? super T,? extends R> mapper)e.g. Stream s = c.stream().map(i -> i * 2);

Various methods of Stream :

1. Processing by collect() method :

This method collects the elements from the stream and adding to the specified collection.

package com.codeFactory.stream;import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;public class Test {
 public static void main(String... args) {
  ArrayList<Integer> i = new ArrayList<>();
  i.add(0);
  i.add(10);
  i.add(20);
  i.add(5);
  i.add(15);
  i.add(25);
  
  List<Integer> i1 = i.stream().filter(x -> x%2 == 0).collect(Collectors.toList());
  System.out.println(i1);
  
  List<Integer> i2 = i.stream().map(x -> x * 3).collect(Collectors.toList());
  System.out.println(i2);
 }
}

Output :

[0, 10, 20]
[0, 30, 60, 15, 45, 75]

2. Processing by count() method :

This method returns the number of elements present in Stream

package com.codeFactory.stream;import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;public class Test {
 public static void main(String... args) {
  ArrayList<Integer> i = new ArrayList<>();
  i.add(0);
  i.add(10);
  i.add(20);
  i.add(5);
  i.add(15);
  i.add(25);
  
  long count = i.stream().filter(x -> x%2 == 0).count();
  System.out.println(count);
 }
}

Output :

3. Processing by sorted() method :

We can use sorted() method to sort elements inside stream
We can sort either based on default natural sorting order or based on our own customized sorting order specified by Comparator object

sorted() — for default natural sorting order
sorted(Comparator c) — for customized sorting order

package com.codeFactory.stream;import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;public class Test {
 public static void main(String... args) {
  ArrayList<Integer> i = new ArrayList<>();
  i.add(0);
  i.add(10);
  i.add(20);
  i.add(5);
  i.add(15);
  i.add(25);
  
  List<Integer> i1 = i.stream().sorted().collect(Collectors.toList());
  System.out.println(i1);
  
  List<Integer> i2 = i.stream().sorted((x1, x2) -> x2.compareTo(x1)).collect(Collectors.toList());
  //List<Integer> i2 = i.stream().sorted((x1, x2) -> x2 - x1).collect(Collectors.toList());
  System.out.println(i2);
 }
}

Output :

[0, 5, 10, 15, 20, 25]
[25, 20, 15, 10, 5, 0]

4. Processing by min() and max() methods :

min()

returns minimum value according to specified Comparator

Optional<T> min(Comparator<? super T> comparator)

max()

returns maximum value according to specified Comparator

Optional<T> max(Comparator<? super T> comparator)package com.codeFactory.stream;import java.util.ArrayList;public class Test {
 public static void main(String... args) {
  ArrayList<Integer> i = new ArrayList<>();
  i.add(0);
  i.add(10);
  i.add(20);
  i.add(5);
  i.add(15);
  i.add(25);
  
  int min = i.stream().min((x1, x2) -> x1 - x2).get();
  int max = i.stream().max((x1, x2) -> x1 - x2).get();
  System.out.println("Min : " + min + ", Max : " + max);
 }
}

Output :

Min : 0, Max : 25

5. Processing by using forEach() method :

This method won’t return anything
This method can take Lambda Expression as argument and apply that Lambda Expression for each element present in stream

package com.codeFactory.stream;import java.util.ArrayList;public class Test {
 public static void main(String... args) {
  ArrayList<Integer> i = new ArrayList<>();
  i.add(0);
  i.add(10);
  i.add(20);
  i.add(5);
  i.add(15);
  i.add(25);
  
  i.stream().forEach(s -> System.out.print(s + " "));
  System.out.println();
  i.stream().forEach(System.out::println);
 }
}

Output :

0 10 20 5 15 25 
0
10
20
5
15
25

6. Processing by toArray() method :

We can use toArray() method to copy
Elements present in the stream into specified array

package com.codeFactory.stream;import java.util.ArrayList;public class Test {
 public static void main(String... args) {
  ArrayList<Integer> i = new ArrayList<>();
  i.add(0);
  i.add(10);
  i.add(20);
  i.add(5);
  i.add(15);
  i.add(25);
  
  Integer[] array = i.stream().toArray(Integer[]::new);
  for(Integer x : array) {
   System.out.println(x);
  }
 }
}

Output :

7. Stream.of() method :

We can also apply stream for group of values & for arrays

1. For group of values

Stream<Integer> s = Stream.of(9,99,999,9999);

2. For Arrays

Double[] d = {152.5, 42.3, 64.2};
Stream<Double> s1 = Stream.of(d);package com.codeFactory.stream;import java.util.ArrayList;
import java.util.stream.Stream;public class Test {
 public static void main(String... args) {
  ArrayList<Integer> i = new ArrayList<>();
  i.add(0);
  i.add(10);
  i.add(20);
  i.add(5);
  i.add(15);
  i.add(25);
  
  Stream<Integer> s = Stream.of(9,99,999,9999);
  s.forEach(System.out::println);
  
  Double[] d = {152.5, 42.3, 64.2};
  Stream<Double> s1 = Stream.of(d);
  s1.forEach(System.out::println);
 }
}

Output :

Java 8 — Streams | Code Factory

Introduction to Stream :

Methods of Stream : filter() and map() :

Differnce between filter() and map() :

Various methods of Stream :

Written by Code Factory