Skip to main content

Introduction to Java 8: Lambda Expressions and Streams

- Ways of representing functions
- pre-built function building blocks
- Set of function composition methods

 - Wrappers around collections
 - map, reduce, filter, forEach
 - Lazy Evaluation
 - Can be made parallel

Lambda is not lisp
Stream is not Hadoop

Why Lambda's in Java
  Ability to pass functions around (Javascript, Lisp, Ruby, Scala etc)
  Functional approach proven concise, useful, and parallelizable

Java 7 version
String[] testStrings = {"", "", ""};
Arrays.sort(testStrings, new Comparator() {
   public int compare(String s1, String s2) {
      return (s1.length() - s2.length());

Lambda version
Arrays.sort(testStrings, (s1, s2) -> s1.length() - s2.length());

 - replaces anonymous inner class' single method
 - No type should be used (Type inferencing)
 - Parens optional for single arg (Parens omitting)
     button.addActionListener(e -> setBg(Color.RED));
 - can refer to local, instance variable
 - are not allowed to modify local variables
 - allowed to modify instance variables
 - this is outer class

  - tells compiler is a functional interface
  - only one abstract method
  - other's won't be able to add more methods, compile time check

Method References
 - E.g., Math::cos or myVar::myMethod


Stream methods
 forEach, map, filter, findFirst, findAny

how to make stream
 - Stream.of(val, val)
 - don't use int use wrappers Integer array

  - strm.toArray(EntryType[]::new)
  - strm.collect(Collectors.toList())
  - strm.collect(Collectors.joining(delim)).toString()


String[] arr = {"a", "b", "c"};

Double[] nums = {1.0, 2.0, 3.0, 4.0, 5.0};
        Double[] squars = Stream.of(nums).map(n -> n * n).toArray(Double[]::new);

Double[] nums1 = {1.0, 2.0, 3.0, 4.0, 5.0};
        Double[] squars1 = Stream.of(nums).filter(n -> n % 2 == 0).toArray(Double[]::new);

Optional squars2 = Stream.of(nums).filter(n -> n % 2 == 0)
                .filter(n -> n > 10).findFirst();

System.out.println(Stream.of(arr).reduce("", String::concat));
System.out.println(Stream.of(nums).reduce(1.0, (n1, n2) -> n1 * n2));

comma, space delimiter.
StringJoiner j = new StringJoiner(", ");
j.add("").add("") etc

Limiting Stream Size
limit(n) - returns a Stream of first n elements
substream(n) - starts with nth element

Comparisons - sorted, min, max, distinct

- Sorting by salary,filter(..).limit(..)
   .sorted( (e1, e2) -> e1.getSalary() - e2.getSalary())

- Richest employee,filter(..).limit(..)
   .max( (e1, e2) -> e1.getSalary() - e2.getSalary()).get()

Checking Matches - allMatch, anyMatch, noneMatch

Predicate, Function & BiFunction, Consumer, Supplier and binaryOperator


John Alert said…
I have read your blog its very attractive and impressive. I like it your blog.

Java Training in Chennai Core Java Training in Chennai Core Java Training in Chennai

Java Online Training Java Online Training Core Java 8 Training in Chennai java 8 online training JavaEE Training in Chennai Java EE Training in Chennai

Popular posts from this blog

JPA 2 new feature @ElementCollection explained

@ElementCollection is new annotation introduced in JPA 2.0, This will help us get rid of One-Many and Many-One shitty syntax.

Example 1: Stores list of Strings in an Entity

public class Users implements Serializable {

    private static final long serialVersionUID = 1L;
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    private List<String> certifications = new ArrayList<String>();

    public Long getId() {
        return id;

    public void setId(Long id) { = id;

    public List<String> getCertifications() {
        return certifications;

    public void setCertifications(List<String> certifications) {
        this.certifications = certifications;

        Users u = new Users();
        u.getCertifications().add("Sun Certified Java Programmer");

Generated Tables

Column --> ID
    Row             1


Validating CSV Files

What is CsvValidator ?
  A Java framework which validates any CSV files something similar to XML validation using XSD.

Why should I use this ?
  You don't have to use this and in fact its easy to write something your own and also checkout its source code for reference.

Why did I write this ?
  Some of our projects integrate with third party application which exchanges information in CSV files so I thought of writing a generic validator which can be hooked in multiple projects or can be used by QA for integration testing.

What is the license clause ?

Are there any JUnit test cases for me checkout ?
 Yes, source

How to integrate in my existing project ?

Just add the Jar which can be downloaded from here CsvValidator.jar and you are good.

Instantiate CsvValidator constructor which takes these 3 arguements

         // filename is the the file to be validated and here is a sample         // list - defines all the fields in the above csv file ( a field has index, type, isOptional, rege…

ArrayList vs LinkedList vs HashSet Performance Comparision

ConclusionsInserting & Reading sequentially from Collection prefer LinkedList/ArrayListInserting & Reading/Deleting by Search/equals from Collection prefer HashSetInserting, ArrayList & LinkedList performs best while HashSet takes double the timeReading, HashSet performs best while ArrayList & LinkedList are marginally lessDeleting, HashSet performs 10 times better than ArrayList & ArrayList performs 4 times better than LinkedList. LinkedList is slow because of sequencial search Bottom line : unless you are not going to iterate using for(Integer i : list ) then prefer HashSet
Inserting/Reading/Deleting integer's from zero till countJDK7Collectionactioncounttime msArrayListInsert1000/1LinkedListInsert1000/1HashSetInsert1000/1ArrayListInsert100005LinkedListInsert100004HashSetInsert100007ArrayListInsert10000011LinkedListInsert10000011HashSetInsert10000021ArrayListGet/Read1000LinkedListGet/Read1000HashSetGet/Read1000ArrayListGet/Read100004LinkedListGet/Read100003Has…