Casting

• Casting means to convert from one primitive type to another or from one related class to another class. (Note: I am using the word convert here, but it is not the technical sense of the word convert, which is different. See Type Conversions.)
  
  
• The syntax for an explicit cast uses the new type or class in parentheses before the reference:

  intObject = (int) byteObject;
  intObject = (int) object.method();
  

• Be careful when casting primitive types.
  
  
• Even casting to a larger type can result in a loss of precision.
  
  
• The term promotion refers to casting to a type that can store a bigger value.
  
  
• It is safest to make your types match and avoid casting, but sometimes you will need it or rely on it.

• For instance, if you need to add 2 to a real number, but store it in an int, you would need to cast it.

• If you don't use the explicit cast, your code will not compile.

• For instance, try writing code that uses this snippet, and then fix it (you'll need to use a cast ...):

  Point p1;
  Point p2;
  int newX;
  
  newX = p1.getX() + 2;
  p2.setLocation(newX, p2.getY());

• More on casting and classes later, but here are some highlights:

  • You can only cast an object to another class if the two classes are related by inheritance.
    
    
  • Casting downward (to a subclass) is automatic. You do not need the (newClass), although you can use it for clarity if you wish.
    
    
  • Casting upwards (to a superclass) requires an explicit class and any additional information that was in the subclass cannot be accessed through the object on the left-hand side of an assignment.
    
    
  • The object on the right-hand side can still access these values and methods because it has not been changed.

• You cannot cast a primitive type to a class (or vice-versa).
  
  
• Java has the Boolean, Byte, Character, Double, Float, Integer, Long and Short type-wrapper classes that correspond to primitive types and allow you to process primitive data as objects. These can be used for converting.
  
  
• Converting is not the same as casting. So, for instance, converting a String to a Double (or double) requires a method call.