Another difference not listed on that page is the use of semicolons. Each line should be able to end with a semicolon (but that can be omitted).
The following code does not compile on Groovy, but compiles on Java:
String s = "hello "
+ "world";
println(s); // Assuming there is a local method with name "println" (available by default in Groovy but you have to create it in Java)
