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