Find the longest word in a given string?

import java.util.*;
public class Main
{
static void lgWord(String a)
{
int n=a.length(),i=0,j=0,max=0,st=0,en=0;
for(;i<=n;i++)
if(i==n||a.charAt(i)==' ')
{
int c=i-j;
if(c>max)
{
max=c;
st=j;
en=i-1;
}
j=i+1;
}
for(int m=st;m<=en;m++)
System.out.print(a.charAt(m));
}
public static void main(String[] args)
{
Scanner s=new Scanner(System.in);
String str=s.nextLine();
lgWord(str);
}
}