Inner and Nested classes

 package com.company.bean;

public class Kia {

    public static class A { // nested class or static class
        public static void foo() {
            System.out.println("A");
        }
    }

    public class B { // inner class or instance class
        public void foo() {
            System.out.println("B");
        }
    }
}

package com.company;

import com.company.bean.Kia;

public class Main {

    public static void main(String[] args) {
        Kia.A a = new Kia.A();
        Kia.B b = new Kia().new B();

        a.foo();
        b.foo();
        Kia.A.foo();
        System.out.println(a.getClass().getName());
        System.out.println(b.getClass().getName());
    }
}
Outcome:
A
B
A
com.company.bean.Kia$A
com.company.bean.Kia$B

As we can see nested classes must be static, however inner classes instance.
And another important fact is there are anonymous(inner classes after compiling.