Casting:

Casting is the term used when you change one primitive data type into another one.
You do not need to cast when you're going from a smaller data container to a larger one. For example, a long is a longer integer than an int is, so there is no problem putting an int into a long. However, if you want a long to become an int, you have to tell the compiler that you actually know what you're doing (and that you haven't just made a sloppy mistake).

Read this link: "Type Casting in Java"

Diagram

Results of Casting

int i = 5;
int j = 2;
double result;

result = i / j; 			//integer division; 	result=2 EVEN THOUGH IT IS A DOUBLE
result = (double) i / (double) j	//real division; 	result=2.5 (only one of i or j needs to be cast)

Java will implicity cast operants in a mixed expression to match the precision of the variable storing the result.

Sample Code snippet:

double d = 8.8e15;
int x = (int)d;
System.out.println(x);

Casting Objects (more later)

You can also cast objects to their daughter class (if they are the correct type)

abstract class Animal{
 public abstract void move();
}
class Shark extends Animal{
 public void move(){
  swim();
 }
 public void swim(){}
 public void bite(){}
}
class Dog extends Animal{
 public void move(){
  run();
 }
 public void run(){}
 public void bark(){}
}

...

void somethingSpecific(Animal animal){
 // Here you don't know and may don't care which animal enters
 animal.move(); // You can call parent methods but you can't call bark or bite.
 if(animal instanceof Shark){
  Shark shark = (Shark)animal;
  shark.bite(); // Now you can call bite!
 }
 //doSomethingSharky(animal); // You cannot call this method.
}