remove extra blank spaces from string in java

1import java.util.Scanner;
2class RemoveExtraSpace{ //starting of class
3    public static void main(String[] args){ //starting of the main function
4        Scanner sc=new Scanner(System.in); //declaring an object of the Scanner class
5        String input,output=""; 
6        char c;
7        int i,len;
8        System.out.println("ENTER A SENTENCE.");
9        input=sc.nextLine().trim(); //accepting the input
10        len=input.length();
11        for(i=0;i<len;i++){ //outer for loop to traverse each character
12            c=input.charAt(i);
13            output+=c;
14            if(c==' '){
15                while(input.charAt(i)==' '){ //inner while loop to skip through repeated spaces
16                    i++;
17                } //end of while loop
18                i--; //decrementing i by 1 so that the immediate character after space is taken
19            }
20        } //end of for loop
21        System.out.println(output); //printing the result
22    } //closing of main function
23} //closing of class