In my career, I've done a bit of switching back and forth between Emacs and various IDE's. One of the IDE features I've come to depend on is quick access to the compiler. Typically, IDE's make it possible to compile your project with a keystroke, and then navigate from error to error at the press of a key. It's easy to recreate this in Emacs. The following two expressions make Emacs work a lot like Visual Studio in this regard.
(global-set-key [(shift f5)] 'compile)
(global-set-key [f12] 'next-error)
After these forms are evaluated, pressing Shift-F5 invokes the compile command, which asks for a command to be run in an inferior shell, typically make, ant, or some other build utility. The catch is that it runs the command in the directory of the current buffer, which implies that the build script can be found in the same directory as the current source file. For a Java project with a per-package directory hierarchy, this is often not true. There are probably a bunch of ways to fix this, but I've solved it with a Windows NT batch file, ant-up.bat, that repeatedly searches up the directory hierarchy for build.xml. I just compile with ant-up, rather than a direct invocation of ant. This is not the most elegant solution, I'm sure, but it took about five minutes to implement and works well.
@echo off
setlocal
:retry
set last_path=%CD%
echo Searching %CD% ...
if exist build.xml goto compile-now
cd ..
if "%last_path%"=="%CD%" goto abort
goto retry
:compile-now
call ant -k %1 %2 %3 %4 %5
if errorlevel 1 goto failure
goto success
:abort
echo build.xml not found... compile failed
:failure
exit /b 1
:success
exit /b 0