Why Concatenation of two string objects reference not equal to same content string object [duplicate]

Answer 1

1. String s4 = "Buggy" + "Bread";

   The compiler is smart enough to realize this is just the constant BuggyBread which is already referenced in s3. In other words, s4 references the same String as s3 that is in the string pool.

2. String s5 = s1 + s2;

   Here the compiler faithfully translates to a StringBuilder-based concatenation of the contents of the variables, which yields a difference reference than s3. In other words, this is similar to:

   StringBuilder sb = new StringBuilder(s1);     
   sb.append(s2);
   String s5 = sb.toString();
   

Answer 2

 Just try this   
  String s = "Buggy";
  s = s.concat("Bread");
  System.out.println(s);