Categories: Java | How To | Optimization

From Forum Nokia Wiki

Reducing Jar-size: An overview.

This article was submitted by user:atiskov as an entry to the St Petersburg Developer Day competition.

Sometimes a JAR file that contains your application becomes too big to install on the device.

There are two ways of reducing final JAR file:

• Reduce the size of resources that are included in JAR file (pictures, binary files, text resources etc.)
• Reduce the size of class files (files that contain code of your application)

Taking the first approach, you should:

• Use special algorithms that compress text data in your text-files (maybe Huffman algorithm). But at the same time you should place special code in your java-files in order to decode such text-files, and your JAR size can become larger!
• Use pictures that do not contain more colors than mobile-phone supports (often there is no need to store pictures with 24bit depth colors) Try reducing image colour depth in GIMP or Photoshop. See for more information.
• Use a picture resolution that will be small enough to fit your application requirements (no need to store pictures 1280*1024...)

Taking the second approach - there are two types of actions in order to reduce size of class-files:

• Actions that always will help you to reduce size of class-files (less or more)
• Actions that sometimes reduce size of class-files (but they also can increase it!) depending on the situation (code of classes in your application)

First Type - "Less is More"

• Using obfuscaters. Note that on different projects different obfuscaters can show very unlike results.
  • Use different settings of obfuscating process that your current obfuscater allows.
  • Sometimes it is possible to indicate which ZIP - archive program to use (JAR file is a ZIP archive).
  • Try different settings of this archive program
• Make variables, classes, methods and class members final. Constants require less space for storing in class-files (use modifier “final”).
• Erase all your System.out.print's if they don't be valuable for user in release version of your application or introduce variable

public static final boolean LOG_ENABLED = true;

And write

if (LOG_ENABLED)
/*...*/

above invocations of System.out.print's. And before you will make a release version of your application, set LOG_ENABLED to false and use obfuscater (he will cut off stuff from class files)

• Delete unnecessary parameters of methods (that aren't used during method's flow)

Second type:

• Try different visibility modifiers of members and methods (static, public, private).
• Try not to use inner classes.
• You can inline some methods (especially those which are invoked only once per application run), variables, class members and classes (Reduce JAR Size: Replacing classes with arrays).
• Use variables of less size (e.g. ‘byte” occupies 8 bit and “long” occupies 64 bit).
• If it is possible try to combine all variables or class members of the same type in the array (Reduce JAR Size: replace class variables with an array).
• Initialize your arrays by values that are stored not in code, but in resource files (e.g. text data).
• Use low-level API when drawing simple things (e.g. do not store white background in 16bit-colored picture in PNG-format – simply use Graphics.fillRect method with parameters of width and height of screen and appropriate color).
• Sometimes it is possible to replace method by a constant – do this. (e.g. value of screen resolution can be stored in the final class members).
• Replace "switch" conditions by "if-else" or even simply "if" (Reduce JAR Size: Replacing "switch" condition by "if").

See also

• How to optimize PNGs to reduce JAR size
• Reduce JAR Size