Java lambdas and streams –are they better than for

loops?Aleksander Radovan, King ICT

Branko Mihaljević, HUJAK

Project Lambda

Simon Ritter: JDK 8 MOOC – Functional Programming in Java with Lambdas an Streams

Lambda advantages

• Functional programming paradigm

• Easier to distribute processing of collections over multiple threads(CPU cores)

• Stream API

• Faster than conventional loops?

Benchmarking hardware and methodology

• CPU: Intel Core i7-4702MQ (4 cores)

• 32 GB RAM

• SSD Samsung 850 EVO 500 GB

• Eclipse Neon

• Java 8 update 121

• Generating objects with random values

• Comparing times needed to finish a specific tasks with iterators, loop, comparators, sequential and parallel streams

• Every measurement was performed 10 times, the average values were taken intoconsiderations

Domain model

Random object generator

Strategies

Iterator

Sequential stream

Comparator

Foreach loop

Parallel stream

Iterator strategy implementation

Foreach loop strategy implementation

Comparator strategy implementation

Stream API strategy implementations

1. Case: finding the youngest programmer (10 objects)

• Results (ms):

0,1

0,4

0,9

4,5

2,7

0 1 2 3 4 5

Iterator

ForLoop

Comparator

Sequential Stream

Parallel Stream

Finding the youngest programmer(10 objects)

1. Case: finding the youngest programmer (100 objects)

• Results (ms):

0,4

0,4

1,4

5,2

2,9

0 1 2 3 4 5 6

Iterator

ForLoop

Comparator

Sequential Stream

Parallel Stream

Finding the youngest programmer (100 objects)

1. Case: finding the youngest programmer (1.000 objects)

• Results (ms):

0,9

0,9

2,7

5,4

2,7

0 1 2 3 4 5 6

Iterator

ForLoop

Comparator

Sequential Stream

Parallel Stream

Finding the youngest programmer (1000 objects)

1. Case: finding the youngest programmer (10.000 objects)

• Results (ms):

3,1

2,7

11,4

7,8

4,3

0 2 4 6 8 10 12

Iterator

ForLoop

Comparator

Sequential Stream

Parallel Stream

Finding the youngest programmer (10.000 objects)

1. Case: finding the youngest programmer (100.000 objects)

• Results (ms):

14

14,9

79,7

22,4

10,3

0 20 40 60 80 100

Iterator

ForLoop

Comparator

Sequential Stream

Parallel Stream

Finding the youngest programmer (100.000 objects)

1. Case: finding the youngest programmer(1.000.000 objects)

• Results (ms):

39,3

33,1

732,7

79,3

43,1

0 200 400 600 800

Iterator

ForLoop

Comparator

Sequential Stream

Parallel Stream

Finding the youngest programmer (1.000.000 objects)

1. Case: finding the youngest programmer(summary)

• Results (ms):

0

20

40

60

80

100

10 100 1000 10000 100000 1000000

Finding the youngest programmer (without Comparator solution)

Iterator ForLoop Sequential Stream Parallel Stream

2. Case: finding programmer with the highest salary(summary)

• Results (ms):

0

10

20

30

40

10 100 1000 10000 100000

Finding programer with the highest salary (without Comparator solution)

Iterator ForLoop Sequential Stream Parallel Stream

Filtering strategy implementations

Filtering strategy implementations

3. Case: filtering programmers by lastname

• Results (ms):

0

5

10

15

20

25

30

10 100 1000 10000 100000

Filtering programmers by lastname

Iterator ForLoop Sequential Stream Parallel Stream

Grouping strategy implementations

Grouping strategy implementations

Grouping strategy implementations

4. Case: grouping programmers by programminglanguage

• Results (ms):

0

20

40

60

80

100

120

10 100 1000 10000 100000 1000000

Grouping the objects into a map

Iterator ForLoop Sequential Stream

Conclusions

• Stream API methods not the best choice in every situation

• In case of arrays (instead of collections), the difference is more drastic

• With fewer objects (< 1000) the conventional (older) way is more appropriate

• The object type is also important (comparing BigDecimals, LocalDates…)

• The streams have certain amount of overhead

• But, „one-liner-programming” is fancy

THANK YOU!