eclipse default build and ant build

Cntrl+B( or clean-> build) will build complete java project under eclipse environment. Is this build uses project which is configured def开发者_JAVA技巧ault build or it builds based on the eclipse plugin?

one of the java application I have seen is eclipse build will build complete project and depoy in the tomcat directory. How this is happening?

You might have seen the deployment feature with an Eclipse configured with WTP (Web Tools Platform).
WTP is featured in the Eclipse IDE for Java EE Developers and Eclipse IDE for JavaScript Web Developers, and contributes to many of the other Indigo packages.

WTP is able to deploy an app in a Tomcat (or in a local Tomcat within Eclipse itself).
See also "How does eclipse deploy web applications using WTP?"

You can see an example a a build and deployment in "HowToSetupEclipseWtp".