How To Transfer The Value Of A Variable From One Class To Another

I am developing a program that seems to need to transfer the value of a variable from one class to another. However, neither of the classes is the main class.

This simplified code should make my problem clear:

This is my main class where I create runone from Class1 and runtwo from Class2:

public class MainClass {
public static void main(String[] args) { 
Class1 runone = new Class1();
Class2 runtwo = new Class2(); 
} 
}

This is Class1 where I set up x and give it the value 20. I also have a getter-method to be able to access the value of x from other classes.

public class Class1 {
int x = 20;
public int getX(){
return x;
}}

This is Class2, where I try to access the value of x that was set up in runone.

public class Class2 {
int y;
public Class2() {
y = runone.getX + 10;
System.out.println(y);
}
}

Unfortunately, I get the error message "runone cannot be resolved to a variable."

What do I do to be able to access the variable x (that is set up in Class1) from Class2?