Auto-boxing

• Auto-boxing: Starting with Java 5.0, conversion between primitive types and the corresponding wrapper classes is automatic.

Double d = 29.95; // auto-boxing; same as Double d = new Double(29.95);

double x = d; // auto-unboxing; same as double x = d.doubleValue();

• Auto-boxing even works inside arithmetic expressions

Double e = d + 1;

Means:

• auto-unbox d into a double

• add 1

• auto-box the result into a new Double

• store a reference to the newly created wrapper object in e

What is the difference between the types double and Double?

   Answer: double is one of the eight primitive types. Double is a class type.
 

Suppose data is an ArrayList<Double> of size > 0. How do you increment the element with index 0?

   Answer: data.set(0, data.get(0) + 1);