Android™ How to Program, Second Edition

F.6. Default and No-Argument Constructors

Every class must have at least one constructor. If you do not provide any in a class’s declaration, the compiler creates a default constructor that takes no arguments when it’s invoked. The default constructor initializes the instance variables to the initial values specified in their declarations or to their default values (zero for primitive numeric types, false for boolean values and null for references). In Section G.4.1, you’ll learn that the default constructor performs another task also.

If your class declares constructors, the compiler will not create a default constructor. In this case, you must declare a no-argument constructor if default initialization is required. Like a default constructor, ...