* Explain Inheritance.
* How can you prevent overriding a parent class' method in a child class? (Your answer: static methods.)
* What is instantiation?
* How can you instantiate a class in Java?
class User {
   String name;
   int age;
   User(...) {
     ...
   }
}
* What does this do: "User u = new User("Joe", 32);"
* How does Java "stores" references? (https://youtu.be/mywtIhLnpEU)
* How does Garbage Collection work in Java?
* What is pass-by-reference vs pass-by-value? (https://stackoverflow.com/q/40480)
String a = "hello";
String b = a;
int i = 0;
int j = i;
foo(a);
foo(i);
* What is auto-boxing?
int i = 1;
Integer j = 10; // Integer j = Integer.valueOf(10); -> Integer valueOf(int x)
System.out.prinlnt(i + j); // i + j.intValue() -> int intValue()
foo(i); // void foo(Integer x);
bar(j); // void bar(int x);
* What would happen here?
Integer j = null;
bar(j); // void bar(int x);
bar(j.intValue()); // NPE
* What does "type-conversion" mean? (Primitive widening/narrowing conversions: https://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html)
String s = ... // user input
int i = convertUserInputToString(s);
* What is casting? How does it work? What is the cast operator? (How do you use it?)
class Animal {
}
class Snake extends Animal {
}
class Horse extends Animal {
}
Animal a = new Animal();
Horse h = new Horse();
Snake s = new Snake();

Animal a1 = h;
Animal a2 = s;

public void foo(Animal a) {
  Horse h1 = (Horse)a; // success depends on runtime type of "a"
}
foo(new Horse()) // succcess
foo(new Snake()) // fails: ClassCastException
* What kind of modifiers do you know about in Java? (public, protected, private, (default), static, final, abstract, synchronized, transient)
* How can you use the final keyword?
* Can I modify the value of this array?
final int[] arr = new int {1, 2, 3];
...
arr[0] = 42; // arr.set(0, 42) (kind of), this won't work
arr = new int {42, 42, 42}; // this doesn't work
* When can you initialize a final variable?
* What is transient?
* What is synchronized?