New to Java

I am trying to make a program where the user will enter in 4 letter grades, and then it will calculate your gpa, but the user is only prompted once to enter in all the letter grades.

this is what i have



import java.util.*;

public class assignment3b {
public static void main(String[ ] args) {
Scanner input = new Scanner(System.in);

System.out.println("Enter 4 letter grades with no spaces, and in UPPERCASE (ABCD)");
String x ;
x = input.next();


char A, B, C, D, F;
double gpa, grade1, grade2, grade3, grade4 ;

{
if (x.charAt(0).equals('A'))
grade1 = 4.0;
else
if (x.charAt(0).equals('B'))
grade1 = 3.0;

else if (x.charAt(0).equals('C'))
grade1 = 2.0;

else if (x.charAt(0).equals('D'))
grade1 = 1.0;

else if (x.charAt(0).equals('F'))
grade1 = 0.0;
else

System.out.println("grade not valid ");
}

gpa = ((grade1 + grade2 + grade3 + grade4) / 4);

System.out.println("Your grade point average is " + gpa);
}
}


i keep getting this error
assignment3b.java:19: char cannot be dereferenced
if (x.charAt(0).equals('A'))
^
assignment3b.java:22: char cannot be dereferenced
if (x.charAt(0).equals('B'))
^
assignment3b.java:25: char cannot be dereferenced
else if (x.charAt(0).equals('C'))
^
assignment3b.java:28: char cannot be dereferenced
else if (x.charAt(0).equals('D'))
^
assignment3b.java:31: char cannot be dereferenced
else if (x.charAt(0).equals('F'))
^
5 errors



if anyone can look at this i would really be grateful, im just so lost now