Double vs double in java [duplicate]

Question

Possible Duplicate:
Java : different double and Double in comparison

In a sample java program for one of my labs, I have two different methods taking Double and double parameters respectively.
How do I differentiate between them when passing arguments to them?

Answer 1

Double parameter can be null when double can't.

Answer 2

First off you need to understand the difference between the two types. double is a primitive type whereas Double is an Object.

The code below shows an overloaded method, which I assume is similar to your lab code.

void doStuff(Double d){ System.out.println("Object call"); }
void doStuff(double d){ System.out.println("Primitive call"); }

There are several ways you can call these methods:

doStuff(100);
doStuff(200d);
doStuff(new Double(100));

These calls will result in:

"Primitive call"
"Primitive call"
"Object call"

Answer 3

- double is a primitive type, where as Double is a wrapper object.

- One of the most common use of Wrapper objects is with Collection .

Eg:

List<Double> d = new ArrayList<Double>();

- In Java 5 a mechanism called Autoboxing has been introduced to convert between the two directly.

Eg:

double d = 10.41;
Double wrapper = d;

Answer 4

Double is reference type and double is value type.

The Double class wraps a value of the primitive type double in an object. An object of type Double contains a single field whose type is double." link

As @Fess mentioned and because Double is reference type it can be null.

If you want you can explictly convert from Double to double with .doubleValue() method and viceverrsa with new Double(1.0).

Also as @millimoose said:

You should use X.valueOf() instead of new X(). The valueOf methods are allowed to cache the boxing types to reduce memory use. (Not sure this is done for Doubles but it's a good habit to get into.)"