$find . -name “*.java” -exec sed -i ’s/foo/bar/g’ {} ;

[aafghani-03:~/test amirafghani]$ find . -name "*.java" -exec sed -i 's/foo/bar/g' {} ;
sed: 1: "./bar.java": invalid command code .
sed: 1: "./foo.java": invalid command code .

find . -name "*.java" -exec sed -i '' s/foo/bar/g {} ;

find . -name "*.java" -exec sed -i s/foo/bar/g {} ;