Using next() in the parameter of if/else statement

Question

So I am pretty sure I am using next and hasNext incorrectly... I am attempting to input a string of ACGT characters and then count the individual resulting letters. Thanks in advance.

import java.util.Scanner;

public class A1Novice {
    public static void main(String[] args){
        String input = "";
        Scanner s = new Scanner(System.in);
        Scanner j = new Scanner(input);
        System.out.println("Enter nucleobases (enter end when done)");
        while(true){
            input = s.next() + input;
            if(s.next().contains("end")){
                break;
            }
        }
        process(j, input);  
    }

    public static void process(Scanner j, String input){
        int a = 0, c = 0, g = 0, t = 0;
        while(j.hasNext()){
            if (j.next()=="A"){
                a++;
            }
            else if(j.next()=="C"){
                c++;
            }
            else if(j.next()=="G"){
                g++;
            }
            else if(j.next()=="T"){
                t++;
            }
            else{
                System.out.println("A count: " + a);
                System.out.println("C count: " + c);
                System.out.println("G count: " + g);
                System.out.println("T count: " + t);
                break;
                }
         }

    }
}

Answer 1

As already written you have to put your next element in a local variable.

This is not enough however: please never use == to compare strings. Use String's method equalsinstead or even equalsIgnoreCase.

You should use something like :

String val = j.next();
if(val.equals("A")){ // you could use val.equalsIgnoreCase("A") to be case insensitive
    ...
} else if (val.equals("B")){
    ...

As suggested in aljipa's answer, you you to use a switch. If you want your test to be case insensitive can can also write something like:

String val = j.next();
switch (val.toUpperCase()) {
    case "A":
        a++;
        break;
    case "B":
        ...