Disable breadcrumbs: This will speed up switching between files.
Disable theme animations: Go to Window -> Preferences -> General -> Appearance -> uncheck the 'Enable Animations' checkbox.
Switch to the classic theme: Go to Window -> Preferences -> General -> Appearance -> select the classic theme. Restart eclipse once if you do not see any immediate changes or performance improvement.
Upgrade to a latest version: Juno (version 4.2.x) had several issues but many of these have been addressed and fixed in version 4.2.2.
Disable unnecessary plugin load on startup: Go to Window -> Preferences -> General -> Startup and Shutdown -> uncheck all plugins which don't need to be loaded on startup.
Use the latest JDK for launching Eclipse.
Minimalize file editors: This tip will speed up switching between files and is especially important for Java file editors. Try to disable file editor features which you don't use - e.g. hide line number, disable code folding, disable range indicators.
These settings can be controlled via Window -> Preferences -> General -> Editors -> Text Editors.
Disable automatic builds: This preference might vary from project to project. Automatic builds might not affect small projects but can cause a major hindrance for huge projects. This setting can be toggled from Project -> Build Automatically.
Close unused projects: Right click on a project -> Close Project.
Increase the autocomplete/content-assist timeout: Java content assist is known to timeout very often in Eclipse Juno. This is a reported bug and should be fixed in newer Juno releases. Until then, the content assist timeout can be increased by setting this flag in the eclipse.ini file
: -vmargs -Dorg.eclipse.jdt.ui.codeAssistTimeout=60000.
Also check this.
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