Indika Maligaspe is a developer, designer, architect and trainer specialized in Java and .NET with over 13 years of experience. The document discusses how to write efficient Java code by understanding how memory is used in the JVM and its different areas. It also compares different Java collections and their memory usage, and how to analyze a Java application's performance using tools like VisualVM and JConsole.

1. Reservations Gateway Inc.
YOUR LINK to e-TRAVEL SOLUTIONS
- Efficient ProgrammingCreating memory efficient
Applications
“Any intelligent fool can make things bigger and more complex...
It takes a touch of genius - and a lot of courage to move in the
opposite direction”
- Albert Einstein
Indika Maligaspe
October 2013

2. Intro...

K. Indika Maligaspe

Developer, Designer, Architect , Trainer

Tech Geek specialized in JAVA and .Net

Over 13 years if experience in IT / Web Technologies

Lover of almost all sports...

http://www.linkedin.com/profile/view?id=201732082&trk=nav_responsive_tab_profile
Indika Maligaspe
October 2013

3. What we will cover

Understanding the memory modal of JVM

Efficient usage of Java

What's in a Collection

How to analyze

QA
Indika Maligaspe
October 2013

4. Understanding the memory
modal of JVM

The JVM is made up of several areas

Threads & Stack

Heap

Non Heap Permanent generation
Indika Maligaspe
October 2013

5. Understanding the memory
modal of JVM
Three main areas that effects performance

Young Generation


Short lived, smaller footprints


Newly Created Objects
Broken down to 3 areas as Eden & 2 Survivor Spaces
Old Generation


GC runs less frequently

Indika Maligaspe
Where older objects are maintained
Larger Footprints
October 2013

6. Understanding the memory
modal of JVM

Three main areas that effects performance cntd.

Permanent Generation

Meta data about the objects in the heap

Information about classes and methods
Indika Maligaspe
October 2013

7. Understanding the memory
modal of JVM
Indika Maligaspe
October 2013

8. Efficient usage of Java
Anatomy of a Java Object - Integer
public static void main(String[] args){
int integer = 10;
}
public static void main(String[] args){
Integer integer = new
Integer(10);
}


Indika Maligaspe
Memory allocation of an int = 32bits
Memory allocation of an Integer Object = 128bits (4:1)
October 2013

9. Efficient usage of Java
Anatomy of a Java Object
public static void main(String[] args){
int integer = 10;
}
public static void main(String[] args){
Integer integer = new
Integer(10);
}
Indika Maligaspe
October 2013

10. Efficient usage of Java
Anatomy of a Java Object
Indika Maligaspe
October 2013

11. Efficient usage of Java
Anatomy of a Java Object - Strings
public static void main(String[] args){
String myString = new
String(“MyString”);
}


Indika Maligaspe
128 bits of char data, stored in 480 bits of memory
Maximum overhead is char * 24
October 2013

12. Efficient usage of Java
Typical inefficient code
public static void main(String[] args){
1. String[] constVals = {“A”,”B”,”C”,”D”};
2. String valToCheck = “D”;
3. Integer indexToCheck = new Integer(0);
While(loop *10){
4. String toSave = new String();
SaveData(....,...,....,toSave);
}
While(loop *10){
5. Integer bookingData = new Integer(rs.getInt(1));
6. Integer retries = new Integer(rs.getString(2));
}
}
Indika Maligaspe
October 2013

13. Efficient usage of Java
Another String Problem
public static void main(String[] args){
1. String s1 = “Hello”;
2. String s2 = “World”;
3. String s3 = s1 +s2
}
The above is equal to String s3 = new StringBuilder(String.valueOf(s1)).append(s2).toString();


Avoid String appending
Use StringBuffers
Indika Maligaspe
October 2013

14. Efficient usage of Java
Efficient usage of Java - Summary

Objects are much larger the the data you store in them.

Use PDT's where ever possible

Avoid using new instances and re-use existing instances
as mush as possible

Avoid String operations, at least unless you must

Minimize objects that are long lasting and not used they
will be moved to old generation and a GC in old gen is
stop the world
Indika Maligaspe
October 2013

15. What's in a Collection
Each Java collection does different functionality and they
have different memory usages
java.util.HashSet
java.util.HashMap
java.util.Hashtable
java.util.LinkedList
java.util.ArrayList
Indika Maligaspe
October 2013

16. What's in a Collection
HashMap - java.util.HashMap

Implementation - “An Object that maps keys and values
. A map cannot
contain duplicate keys, each key can map to at most one value

Implementation is an array of HashMap$Entry Objects

Default capacity is 16 entries

Empty size is 128 bytes

Overhead is 48 bytes for HasMap, plus (16 + (entries* 4 bytes)) for an array and
the overhead of HashMap$Entry objects
Indika Maligaspe
October 2013

17. What's in a Collection
LinkedList – java.util.ArrayList

Implementation - “An ordered collection (AKA sequence). The user of this
interface has precise control over where in the list each element is inserted.

Implementation is an array of Objects

Default capacity is 10 entries

Empty size is 88 bytes

Overhead is 32 bytes for ArrayList, plus (16 + (entries* 4 bytes)) for an array

For a 10,000 entry ArrayList, the overhead is - 40k
Indika Maligaspe
October 2013

18. What's in a Collection
HashMap$Entry

Each HashMap$Entry contains

Int
KeyHash

Object
next

Object
key

Object
value

Additional 32 bytes per key <> value entry

Overhead of a HashMap is therefore – 48 bytes, plus 36 bytes per entry

For a 10,000 entry HashMap, the overhead is - 360k
Indika Maligaspe
October 2013

19. What's in a Collection
Summary of Collections
Collection
Default Capacity
Empty Size
10k Overhead
HashSet
16
144
360k
HashMap
16
128
360k
Hashtable
11
104
360k
LinkedList
1
48
240k
ArrayList
10
88
40k
StringBuffer
16
72
240k
Indika Maligaspe
October 2013

20. What's in a Collection
Hash* collections vs Others

Hash collections are much larger (almost 9x of an ArrayList)

Additional size helps search / add / remove (performance is constant to Hash
collections but linear to ArrayList)

Really know when to use what and use properly
Indika Maligaspe
October 2013

21. How to analyze
Several tools available to analyze performance within the
JVM

VisualVM - Production / Development

Eclipse – Memory Analysis Tool (MAT) - Development

Jconsole - Development

Just reading hprof - Production / Development

Nagios – Production

NewRelic - Production
Indika Maligaspe
October 2013

22. How to analyze
Most of the tools will give

Memory Usage (Heap / Perm etc..)

CPU stats for JVM

GC usage and behavior

Threads and how threads are being used

Hot spots
Indika Maligaspe
October 2013

23. Thank You
Reservations Gateway Inc.
YOUR LINK to e-TRAVEL SOLUTIONS
Reservations Gateway Inc.
Reservations Gateway Inc.
11654 Plaza America Drive , Unit 645
Reston, Virginia 20190-4700
USA
Tel :
Fax :
Email :
Web :
Indika Maligaspe
703 286 5331
703 433 0146
info@rezgateway.com
www.rezgateway.com
October 2013