Automatic boxing and unboxing

Starting with version 5.0, Java will automatically do the boxing and unboxing operations.

• Automatic boxing takes place when we directly assign a value of a primitive type to an object of a wrapper class, without explicitly invoking the constructor via new. In this case, the call to the constructor is automatically inserted by the Java compiler.

  Example: The three statements we have seen before performing the boxing operation can be equivalently rewritten in the following simpler way without making use of the constructors.

  Integer anIntegerObject = 25;
  Double aDoubleObject = 3.6;
  Character aCharacterObject = 'A';
  

• Similarly, automatic unboxing takes place when we use an object of a wrapper class instead of a value of a primitive data type. In this case, the Java compiler automatically inserts a call to the appropriate access method.

  Example: The three statements we have seen before performing the unboxing operation can be equivalently rewritten in the following simpler way without making use of the access methods.

  int i = anIntegerObject;
  double d = aDoubleObject;
  char c = aCharacterObject;