What is object field initialization and constructor order in Java

Question

I ended up the following scenario in code earlier today (which I admit is kinda weird and I have since refactored). When I ran my unit test I found that a field initializat

Answer 1

Here's an example of polymorphism in pseudo-C#/Java:

class Animal
{
   abstract string MakeNoise ();
}

class Cat : Animal {
    string MakeNoise () {
    return "Meow";
    } 
}

class Dog : Animal {
    string MakeNoise () {
    return "Bark";
    }
}

Main () {
    Animal animal = Zoo.GetAnimal ();
    Console.WriteLine (animal.MakeNoise ());
}

The Main function doesn't know the type of the animal and depends on a particular implementation's behavior of the MakeNoise() method.

class A
{
A(int number)
   {
    System.out.println("A's" + " "+ number);
   }
}

class B
{
A aObject = new A(1);
B(int number)
    {
    System.out.println("B's" + " "+ number);        
    }
A aObject2 = new A(2);
}

public class myFirstProject {   
public static void main(String[] args) {
    B bObj = new B(5);
   }
}

out: A's 1 A's 2 B's 5

My rules: 1. Don't initialize with the default values in declaration (null, false, 0, 0.0...). 2. Prefer initialization in declaration if you don't have a constructor parameter that changes the value of the field. 3. If the value of the field changes because of a constructor parameter put the initialization in the constructors. 4. Be consistent in your practice. (the most important rule)

public class Dice
{
private int topFace = 1;
private Random myRand = new Random();

public void Roll()
   {
   // ......
   }
}

or

public class Dice
{
private int topFace;
private Random myRand;

public Dice()
    {
    topFace = 1;
    myRand = new Random();
    }

public void Roll()
   {
    // .....
   }
}