Encapsulation
Java allows a class
within another class (nested classes).

package com.minte9.oop.nested_classes;
public class Encapsulation {
public static void main(String[] args) {
System.out.println(
OuterClass.InnerClass.y
);
}
}
class OuterClass {
int x = 10;
static class InnerClass {
static int y = 20;
}
}
Static
The nested classes are the only classes that can be
declare static.

package com.minte9.oop.nested_classes;
public class Static {
public static void main(String[] args) {
A.B.run();
}
static class A {
static int a = 10;
static class B {
public static void run() {
System.out.println(a);
}
}
}
}