if statement using indexOf

for my second input I'm trying to use an if statement to print location of the first "a" but if there isn't an "a" than print there is no a. I keep getting error int cannot be converted to boolean on line (a = noSpace.indexOf("a");) tried to debug but I'm not sure how to fix, first time I've received this error. I've marked line with error >>>

public class ManyStrings 
{
  public static void main(String[] args) 
   {
 //first input
 String title="";
 Scanner input = new Scanner(System.in);
 System.out.print("Enter a statement: ");
 title = input.nextLine();
 int x = title.indexOf(" ");

 System.out.println("The length of the string is "+ title.length()+".");
 System.out.println("The first word is " +"\""+ title.substring(0,x)+"\"");
 System.out.println(title.toUpperCase());

 //second input
 System.out.print("Enter second statement: ");
 String strg2 = input.nextLine();
 String noSpace = strg2.replaceAll("\\s","");
 System.out.println(noSpace.toLowerCase());

 noSpace = noSpace.replaceAll("n","r");
 System.out.println(noSpace);


   boolean a;
 >>>    a = noSpace.indexOf("a");
 if(a=-1) {
   system.out.print("There are no a's in the String.");
  }else {
   System.out.print("location of first a: "+ a);

 }




   }
}