The confusion with how Java handles references stems from how it handles objects. One such instance is the String builder, at first appears as if it is pass-by-reference but what java is really doing is updating the object that the string buffer sb references. It’s creating a new String Builder in the method (adhering to pass-by-value), but that new String Builder references the same object in memory.

public static void main(String[] args){
    StringBuilder sb = new StringBuilder(“pass”);
    mutate(sb);
    System.out.println(sb);
    //prints passvalue
}

private static void mutate(StringBuilder sb){
    sb.append(“value”)
}