package 练习;
import java.util.*;
public class StringBuilder {public static void main(String[] args){Scanner scan = new Scanner(System.in);String r = scan.nextLine();StringBuilder x = new StringBuilder(r);System.out.println(x);}}

奉上错误代码（上面）

package 练习;
import java.util.*;
public class String1 {public static void main(String[] args){Scanner scan = new Scanner(System.in);String r = scan.nextLine();StringBuilder x = new StringBuilder(r);System.out.println(x);}}

看出不同了吗