Java - Summary

============================================
                Coding Style
============================================
-All variables should have meaningful names.
-Constants must be declared as public static final.
-Use collections instead of regular arrays.

============================================
                Polymorphism
============================================
public class Animal{
    public int myInt = 1;
    public String speak(){ return "ha?"; }
    public void eat(int calories){System.out.print("Yammy");}
}
public class Dog extends Animal {
    public int myInt = 2;
    public String speak(){return "woof";}
}
public class Cow extends Animal {
    public String speak(){return "moo";}
    public void getMilk(){....}
    public void eat(int calories){System.out.print("Yammy Yammy");}
}
Cow myCow = new Cow();
Dog myDog = new Dog();
Animal myAnimal = myCow;
myAnimal.speak(); //moo
myAnimal.getMilk(); //error. Animals don't give milk.
myAnimal.eat(1212); //Yammy Yammy

-Shadowing (NOT to use): Animal a = new Dog();
                        System.out.print(a.myInt); // 1

-"Program to interface, not to implementation" - try to define variables so that their type is highest in hierarchy.
i.e. Animal a = new Dog(); and NOT: Dog a = new Dog();

Casting:
Animal a = new Cow(); //implicit up casting
Animal animal = new Cow;
Cow c = (Cow) animal; //legal down casting

AVOID DOWN CASTING AND USE OF instanceof

============================================
      Abstract classes and Interfaces
============================================
-Abstract classes:
public Abstract class Animal{
    protected abstract void speak();
    public void eat(){...}
    public static abstract ... //compilation error
}

public class Dog extends Animal {
    public void speak(){...}
}
public class Cat extends Animal {
} //compilation error. speak() not implemented.
-----------------------------------------------
-Interfaces:
public interface Printable{
    public void print();
}
public class Doc implements Printable{
    public void print(){...}
}

public static void main(String args[]){
    Document d = new Document();
    d.print();
    Printable p = new Printable(); //Compilation error
}

-Interfaces can extend interfaces.

============================================
              Design Patterns
============================================
http://www.tutorialspoint.com/design_pattern/
Useful:
-Delegation
-Factory
-Singleton
-Facade
-Decorator
Behavioral patterns
-Iterator
-Strategy

============================================
                 Collections
============================================
ArrayList - https://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html
LinkedList - https://docs.oracle.com/javase/7/docs/api/java/util/LinkedList.html
useful commands:
sort(), isEmpty(), indexOf(), get(int index), size()

============================================
                 Exceptions
============================================
Exception - a class that implements the Throwable interface.

Syntax:
try
{
Statement A
}
catch(Exception e) //catch exception thrown by Statement A
{
Statement B
}
----
throw NullPointerException; //manually throw exception
----
Checked exceptions - extend the Exception class. Compiler knows about this type of exceptions and will give warnings if something is wrong.
Unchecked exceptions - extend the RuntimeException class.