java - Why is there a problem with a non-static variable being read from main?

Question

String name = "Marcus";
static String s_name = "Peter";

public static void main(String[] args) {    
    System.out.println(name);//ERROR
    System.out.println(s_name);//OK
}

ERROR: Cannot make a static reference to the non-static field name

Answer 1

The reason this causes a problem is that main is a static method, which means that it has no receiver object. In other words, it doesn't operate relative to some object. Consequently, if you try looking up a non-static field, then Java gets confused about which object that field lives in. Normally, it would assume the field is in the object from which the method is being invoked, but because main is static this object doesn't exist.

As a general rule, you cannot access regular instance variables from static methods.