Even after JDK-8134007, it seems javac only folds String-like constants from left to right, and it breaks as soon as non-constant is reached. See e.g.:

public class StaticStringConst {

        static final int INT = 42;
        static final Object OBJ = new Object();
        static final String STR = "Foo";

        public static String m1() {
                return "" + INT + STR + OBJ;
        }

        public static String m2() {
                return "" + STR + INT + OBJ;
        }

        public static String m3() {
                return "" + OBJ + INT + STR;
        }

        public static String m4() {
                return "" + OBJ + STR + INT;
        }
}

m1() folds nicely to "42Foo" + OBJ, but m2() folds only to OBJ + 42 + "Foo".