SED Command to Insert Logging Line in Java File

I need to modify alot of java files so that each method prints a logging message so hopefully sed will do the trick for me.

Here's an example of the file change.

public void someMethod(int x) {
     System.out.println("xx"); // Sed command should add this line to the java file for every method in the file

I tried using the following sed command to look for public as the starting pattern and the ending pattern of right paren, space, left bracket.

sed '/public/,/) {/a System.out.println("xx);' file.java

but this doesn't work.  It prints the logging statement mutliple times after below the public method call.

Any ideas what could be wrong?