replace all spaces in a string with '%20'

//Write a method to replace all spaces in a string with '%20'. You may assume that the string has sufficient space at the end to hold the additional characters,and that you are given the "true" length of the string. (Note: If implementing in Java,please use a character array so that you can perform this operation in place.)

import java.util.Scanner;

class Main {

public static void main(String[] args) {

Scanner s = new Scanner(System.in);

String str =s.nextLine();

Main m = new Main();

int length = str.length();

String result =m.urlify(str.trim().toCharArray(),length);

System.out.println(result);

}

public String urlify(char[] a,int length){

char[] result = new char[length];

int res_size = 0;

for(int i=0;i<a.length;i++){

if(a[i] == ' '){

result[res_size] = '%';

result[res_size+1] = '2';

result[res_size+2] = '0';

res_size+=3;

}else{

result[res_size]= a[i];

res_size+=1;

}

}

return new String(result);

}

}