how to remove empty character literal error

[arpiz]

import java .io.*;
public class indranil
{
    public static void main(String args [])throws IOException
    {
      BufferedReader in=new BufferedReader(new InputStreamReader(System.in));
      int a,i,l,z;
      System.out.println("enter a number a");
           
        a=Integer.parseInt(in.readLine());
    l=a.length();
    for(i=0;i<l;i++)
    {
     char ch=a.charAt(i);
        if (ch=='')
        {
        z=z+1;
    }
}

        System.out.println("the number of spaces in sentence is"+z);
        
    }
}