The string is intercepted by bytes

public class TestSubString {     public static void main(String[] args) {         String a = "abc hello 123";         a = subStr(a,6);         System.out.println(a);     }     public static String subStr(String str ,int end){         int length=0;         char[] ch = str.toCharArray();          String str2 = "";         for(int i =0;i<str.length();i++){ // int num = Character.codePointAt( ch,i); // int num = Character.codePointAt( str,i);             int num = str.codePointAt(i); //The effect of changing the line of code is the same as that of the previous two lines of code, get the current Iterate over the values ​​of the elements. Less than or equal to 255 is one byte, and more than 255 is two bytes             if(num>=0&&num<=255){                 length++;//The number of bytes plus 1





    










            }else{                 length+=2;//Add 2 to the number of bytes             }             if(length<end){ //Continue to loop if the intercepted byte length is not reached, and connect the traversed elements with the str string                 str2+=ch[i];             }else if(length==end){ //just reach the intercepted byte length, exit the loop, and connect the traversed elements with the str string                 str2+=ch[i];                 break;             }else{ //Exceed the length, It is because the current traversal is a Chinese character element, and half of the Chinese character is not intercepted, so it exits the loop directly.                 break;             }         }         return str2; return the new spliced ​​string     } }