My classes are conflicting with each other and I dont know why

So I'm learning java right now and I'm using "sub-programs" just like in C but for some reason when I have both programs it gives me an error "Exception in thread "main" java.util.NoSuchElementException"

Main:

    public static void main(String[] args) {
        System.out.println("Escreva uma string:");
        String s = SubProgram.string();
        System.out.println("The string " +s);
        System.out.println("Escreva um Int:");
        int i = SubProgram.umInt();
        System.out.println("The int: " +i);    
    }
}

Classes:

public class SubProgram {
    public static String string() {
        Scanner scan = new Scanner(System.in);
        String s = scan.nextLine();
        scan.close();
        return s;
    }

    public static int umInt(){
        Scanner scan2 = new Scanner(System.in);
        int num = scan2.nextInt();
        scan2.close();
        return num;
    }
}

If I comment all the "String" class the int one works fine. If I don't comment the String, the String works fine but the int does not

First, lets clarify some terms: neither C nor Java actually use the term "sub program", but if you are not a native English speaker this is an understandable error in translation.

What you have in your program is one class - SubProgram that has 2 "methods" - string and umInt.

These names are not very good, since they are too similar to data types.
It would be preferable to use method names like getString and getInt.

But the real problem is that you are closing System.in.
Just like stdin in C, System.in in Java is a file representing the standard input of your program.

Java has several "wrapper" classes to make working with files more convenient, and Scanner is one of them.

However, if you close the Scanner wrapping the file, you will also close the file.
Note, that Scanner will close not only if you explicitly call close, but also if it goes out of scope - this means if you created the Scanner object in a method, like you do now, once you exit the method the Scanner will close automatically.

This is the part where Java is different from C: there is automatic "cleanup" for a lot of things!

One way to solve your problem is to turn Scanner in to a static memeber of the class, like this:

public class SubProgram {
    private static final Scanner INPUT = new Scanner(System.in);

    public static String string() {
        String s = INPUT.nextLine();
        return s;
    }

    public static int umInt(){
        int num = INPUT.nextInt();

        return num;
    }
}

I added the final modifier which is similar to const in C.
Since you don't want to change this Scanner as long as your program is running, it is better to hold it in a constant.

Also, it is customary to use UPPERCASE for constant names in Java (though it is not required by the language).

• One small note: I used the term "file" for simplicity, but System.in is actually a "stream" (object of type InputStream). Streams is how Java deals with things you can read and write like files and sockets, but for now you can think of it as being similar to FILE * in C bundled with relevant functions like fopen.