Static method in java

Question

I heard that static methods should use only static variables in java. But, main method is also static, right?

Answer 1

To access non-static fields (instance variables) you need to have an instance.
Inside a non-static method, this is used as default instance:

class AnyClass  {

    private String nonStaticField = "Non static";

    void nonStaticMethod() {
        this.nonStaticField = "a text";  // accessing field of this
        nonStaticField = "a text";       // same as before
    }
}

---

Inside a static method there is no this to use as default instance, but you can¹ still access instance variables if you provide the instance:

class AnyClass {

    private String nonStaticField = "Non static";

    static void staticMethod() {
        AnyClass example = new AnyClass();
        example.nonStaticField = "new value for non-static field";
    }
}

1 - the field must also be accessible by Java's access control (declared public or in the same class ...)