class P {
  int x; 
  P(){ this(5); }
  P(int x){ this.x = x; }
}
System.out.println(new P().x);

class A { String f(){ return "A"; } }
class B extends A { String f(){ return super.f() + "B"; } }
System.out.println(new B().f());

class A { 
String f(){
 return "A";
 } }
class B extends A {
 String f(){ 
return "B";
 } }
A x = new B();
System.out.println(x.f());

class A {}
class B extends A {}
A x = new A();
System.out.println(x instanceof B);

String s1 = new String("java");
String s2 = new String("java");
System.out.println(s1.equals(s2) + "," + (s1 == s2));

import java.util.*;
List<Integer> xs = new ArrayList<>();
xs.add(1);
xs.add(2);
System.out.println(xs.get(0) + xs.get(1));

class Base { Base(int x) {} }
class Child extends Base { }