Java Byte Code when constructing String

gistfile1.java

public String a() {
	String msg = "aaa";
	return msg;
}

public String b() {
	String msg = new String("aaa");
	return msg;
}

public String c() {
	String a = "aaa";
	String b = "aaa";
	String c = "bbbb";
	
	return a + b + c;
}

public java.lang.String a();
  0  ldc <String "aaa"> [16]
  2  astore_1 [msg]
  3  aload_1 [msg]
  4  areturn
  
public java.lang.String b();
   0  new java.lang.String [21]
   3  dup
   4  ldc <String "aaa"> [16]
   6  invokespecial java.lang.String(java.lang.String) [23]
   9  astore_1 [msg]
  10  aload_1 [msg]
  11  areturn

public java.lang.String c();
   0  ldc <String "aaa"> [16]
   2  astore_1 [a]
   3  ldc <String "aaa"> [16]
   5  astore_2 [b]
   6  ldc <String "bbbb"> [27]
   8  astore_3 [c]
   9  new java.lang.StringBuilder [29]
  12  dup
  13  aload_1 [a]
  14  invokestatic java.lang.String.valueOf(java.lang.Object) : java.lang.String [31]
  17  invokespecial java.lang.StringBuilder(java.lang.String) [35]
  20  aload_2 [b]
  21  invokevirtual java.lang.StringBuilder.append(java.lang.String) : java.lang.StringBuilder [36]
  24  aload_3 [c]
  25  invokevirtual java.lang.StringBuilder.append(java.lang.String) : java.lang.StringBuilder [36]
  28  invokevirtual java.lang.StringBuilder.toString() : java.lang.String [40]
  31  areturn