Change multiple files by extension to UTF-8 without BOM:
$Utf8NoBomEncoding = New-Object System.Text.UTF8Encoding($False)
foreach($i in ls -recurse -filter "*.java") {
$MyFile = Get-Content $i.fullname
[System.IO.File]::WriteAllLines($i.fullname, $MyFile, $Utf8NoBomEncoding)
}