Indify String Concatenation

I am very interested about this http://openjdk.java.net/jeps/280. And I had a session about this which is presented by @bitter_fox who is one of JDK comitter.

Due to my poor skill, I have no idea about below difference which is the result of java.
Anyway I have to learn more...

code

• Sample.java

public class Sample{
    public static void main(String... args){
        Sample sample = new Sample();
        String a = "a";
        String b = "b";
        String ab = sample.m(a,b);
    }
    String m(String a, String b){
        return a + "(" + b + ")";
    }
}

javap

• JDK8

• JDK9(Indify String Concatenation)