public class StringConcat {
    public static void main(String[] args) {
        String s = "$";
        for (int i = 0; i < 10; i++) {
            s += i;
        }
        System.out.println(s);
    }
}

  public static void main(java.lang.String[]);
    Code:
       0: ldc           #2                  // String $
       2: astore_1
       3: iconst_0
       4: istore_2
       5: iload_2
       6: bipush        10
       8: if_icmpge     36
      11: new           #3                  // class java/lang/StringBuilder
      14: dup
      15: invokespecial #4                  // Method java/lang/StringBuilder."<init>":()V
      18: aload_1
      19: invokevirtual #5                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      22: iload_2
      23: invokevirtual #6                  // Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder;
      26: invokevirtual #7                  // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
      29: astore_1
      30: iinc          2, 1
      33: goto          5
      36: getstatic     #8                  // Field java/lang/System.out:Ljava/io/PrintStream;
      39: aload_1
      40: invokevirtual #9                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
      43: return