请问字符串解码问题

Question

import java.io.UnsupportedEncodingException;
public class ziFuChuan{
public static void main(String arg[]){
String hello = "Hello world 世界你好";
try{
      hello = new String(hello.getBytes(), "GB2312");
      byte[] b=hello.getBytes("gb2312");
      System.out.println(b.length);//输出20      hello = new String(hello.getBytes(), "UTF-8");
System.out.println(hello.length());//输出18 byte[] b1=hello.getBytes("UTF-8");
System.out.println(b1.length);//输出28
System.out.println(hello.length());//输出18    }
    catch(UnsupportedEncodingException e){}
}
}

Answer 1

这个是源程序，还是搞不懂怎么得出来的
import java.io.UnsupportedEncodingException;
public class ZiFuChuan{
public static void main(String arg[]){
String hello = "Hello world 世界你好";
try{
      //hello = new String(hello.getBytes(), "GB2312");
      byte[] b=hello.getBytes("gb2312");
      System.out.println(b.length);//输出20      String hello1 = new String(hello.getBytes(), "gb2312");
  System.out.println(hello1.length());//输出16
//hello=new String(hello.getBytes(),"UTF-8");//----(1)
byte[] b1=hello.getBytes("UTF-8");
System.out.println(b1.length);//输出24,如果加上（1）输出28
String hello2=new String(hello.getBytes(),"UTF-8");
System.out.println(hello2.length());//输出18    }
    catch(UnsupportedEncodingException e){}
}
}