Writing High-Performance Applications With the Java™ Foundation Classes (JFC/Swing) API

Steve Wilson
Java Performance Engineering
Sun Microsystems

Introduction

• The JFC/Swing API has a reputation for being slow

• It doesn’t have to be

• Well written JFC/Swing GUIs can be highly interactive and responsive

Presentation Goal

• Understand the key concepts required to construct fast, responsive graphical user interfaces using the JFC/Swing toolkit

Overview

• What is Performance?

• High-Level Strategies

  • Process
  • Tools

• Low-Level Tactics

  • Model/View/Controller (MVC)
  • Multi-threaded GUIs
  • Deployment options

The Book

What Is Performance?

• Computational Performance

• RAM Footprint

• Startup Time

• Scalability

• Perceived Performance

Performance Process Diagram

Profiling Tools

• “Hot” methods

  • Slow
  • Called often

• Call stacks

• Memory allocations

  • Allocation takes time
  • Track memory leaks
  • Decrease footprint

Commercial Profiling Tools

• Excellent commercial tools are available:

  • OptimizeIt from VM Gear
  • JProbe from Sitraka
  • TrueTime from Compuware

• See session BUS-574 for more info

Tactics Overview

• Little Objects

• Model/View/Controller (MVC)

  • Speed
  • Footprint

• Responsiveness (Multi-Threaded GUIs)

• Deployment

• A new goodie in the J2SE™ 1.4 release

Object Allocation Costs

• Classic VM (1.1.x), costs are significant for all objects

• Java HotSpot™ VM costs are much lower for small short-lived objects

• You still want to avoid thrashing the GC

• Remember initialization costs

Returned Copies

• Mutable objects often copied to ensure encapsulation

MVC and Performance

• Historically praised for reusability and maintainability

• Also helps performance!

• Move control of data into app space

• You determine optimal handling for:

  • Allocation
  • Representation
  • Binding between data and model

JFC/Swing API’s Model/Renderer System

Loading a ComboBox

• Two ways to accomplish task

• One is fast, one is slow

JComboBox: Try #1

• Takes 1000 milliseconds

• Doesn’t scale well

• Constantly firing update events

JComboBox: Try #2

• Takes only 50 milliseconds

• Scales well

Prototype Cells

• JList and JComboBox must scan all entries to determine proper size for layout

• This can be slow

• Can use new methods to short-cut this for the case where know the largest entry

  • JList.setPrototypeCellValue(Object)
  • JComboBox.setPrototypeDisplayValue(Object)

Prototype Cell Example

Prototype Cell Performance

Time to display Component with 10,000 items in
milliseconds on 866 MHz PC
Small numbers are good

TableModel and Footprint

• JTable can display large amounts of data

• How best to store it

• You can decide based on your problem!

Big Model (Simple)

• Uses 4MB before first cell is set

Big Model (Sparse)

• Uses about 1KB before first cell is set

JFC/Swing APIs Default Models

• Simple

• General Purpose

• Not highly tuned for your app

• For large data sets you’ll usually want a custom model

Multi-threaded GUIs

• JFC/Swing technology is single-threaded

• You can use multiple threads in a JFC/Swing API-based app

• You just need to follow the rules

• Effective use of threading is required to build complex, responsive GUIs

Responsiveness

• User actions produce immediate feedback

• Let them know what’s going on

• Let them interrupt what’s going on

• Let them know why they’re waiting

JFC/Swing API and Threading

• Responsiveness often requires multi-threading

• You need to understand the JFC/Swing API’s thread model

JFC/Swing API’s Thread Model

• JFC/Swing API-based UIs are single threaded

• Most actions that touch GUI must take place on the AWT event thread

• Events occur on event thread

• Painting occurs on the event thread

• Life is usually simple!

Single Thread Rule

• Touch JComponents only from AWT event thread after they’re realized

  • setVisible(true)
  • show()
  • pack()—yes pack counts too!

• Construct GUI on any thread

Exceptions to the Rule

• These methods are safe from any thread:

  • repaint()
  • invalidate()
  • revalidate()

• Other methods as marked

• Otherwise

  • invokeLater()
  • invokeAndWait()

When to Use Threads?

• Long or indeterminate tasks

• Repetitive tasks

Long Tasks

• Very complex calculation

• Big database query

• Anything that touches the network

• Anything that can block!

• Don’t block the event thread!

Example #1: DB Query

• User Clicks JButton

• Event comes to listener on event thread

• You do query (on event thread) <- STOP

• Event thread waits

• Results return

• Update GUI (on event thread)

Example #2: Better Query

• User Clicks JButton

• Event comes to listener on event thread

• You do query (on a new thread) <- BETTER

• Event thread continues

• Results return

• Update GUI (with invokeLater)<- BETTER

Using SwingWorker

• Get class from “JFC/Swing Connection”

Repetitive Actions

• Polling for a condition

• Doing an animation

Use javax.swing.Timer

• There is also java.util.Timer

Deployment

• JAR Files

• Java™ Plug-In technology

• Java™ Web Start software

“Java Archives”

• JAR files package network deployed code and resources

• Major improvements in download time

• SwingSet Example on LAN:

Sticky JARs

• New for 1.3, control of applet caching in plug-in

  

• http://java.sun.com/j2se/1.3/docs/guide/misc/ appletcaching.html

Java™ Web Start Software

• Java Web Start software allows for “sticky” applications

• Also allows for application components to be downloaded on demand

• http://java.sun.com/products/javawebstart

Volatile Image—New for 1.4

• New Java™ 2D API VolatileImage class

• Allows the Java 2D API to use hardware accelerated video

• JFC/Swing API’s double-buffer tweaked to use

• Makes big performance improvement for some apps

• See session TS-1314 for more details

Summary

• Understand JFC/Swing API’s MVC architecture

  • Models
  • Renderers

• JFC/Swing API’s default renderers are not tuned for your app

• Use multi-threading to improve responsiveness

• Packaging matters

• Performance improvements coming in 1.4