Casting vs Appending

Question

Consider the following code:

int x = 300;
int y = 200;

float new_x = 300/1.2f;           // Appending 'f' to the end of operation
long new_y = (long)Math.pow(y,7); //Casting

When performing both operations my compiler wants to convert new_x and new_y to double.

But by appending or casting I can force the compiler to keep it the way I want.

My question is:

What is the difference between the casting method and the appending method

Answer 1

Appending a letter (l,d,f) to a LITERAL is only to specify to the compiler what type you mean that literal to be. If you write a literal in your source code, by default it is considered an int or a double.

Casting on the opposite is actually converting an existing value (for example the double returned by Math.pow) into another java type.

Casting a primitive can cause truncation. For example, a double casted to an int or to a long will loose the decimal part, converting a big long to int can result in a totally different number (if the long is higher than Integer.MAX_VALUE), and converting to short or byte is the same with stronger limits.

Casting is a much wider concept, you can cast instances and not only primitives :

public void aMethod(Number n) {
  Long l = (Long)n;  // Obviously will throw exception if you don't call it with a long
}

Casting can cause a ClassCastException if you try to cast an instance to something it is not.

This does not happen between primitives, which are automatically casted by the jvm.

For example calling :

aMethod(1);

Will throw an exception, even if a primitive int can be casted to a primitive long, an instance of Integer can't be cast to an instance of Long, as much as an instance of Person can't be cast to Dog.