import java.util.*;
public class String1 {
    public static void mian(String[] args)
    {
        Scanner sc = new Scanner (System.in);
        String str = new String();
        System.out.print("Enter a string:");
        str = sc.next();
        System.out.println("The length of the string is" + str.length());
        System.out.println("The character at position 3 is" + str.charAt(2));
        System.out.println("Characters 2 to 4 are" + str.substring(1,4));
        System.out.println(str.concat("was the string entered"));
        System.out.println("This is upper case:" + str.toUpperCase());
        System.out.println("This is lower case:" + str.toLowerCase());
    }

}
执行后显视IWAV0048I Java Bean String1 started with null constructor
请问什么原因?[]

[[it] 本帖最后由 yxishe 于 2008-12-4 22:45 编辑 [/it]]

你main写成mian了.....................

呵呵  这都能写错！！！
  出错了 自己先检查，看书，在检查。别急一定可以查出来得 你用myeclipse 编写吧。哪里有语法错误直接就提示了
！