Chapter 3 Data Types, Variables, And Arrays In Java

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Although you might think that using a byte or short would be more efficient than using an int in situations in which the larger range of an int is not needed, this may not be the case.

...Since Java is strongly typed, you might be wondering how it is possible to assign an integer literal to one of Java’s other integer types, such as byte or long, without causing a type mismatch error. ... When a literal value is assigned to a byte or short variable, no error is generated if the literal value is within the range of the target type. 

...Although the preceding examples have used only constants as initializers, Java allows variables to be initialized dynamically, using any expression valid at the time the variable is declared.


...Within the if block, x can be used because code within a block (that is, a nested scope) has access to variables declared by an enclosing scope.


...If a variable declaration includes an initializer, then that variable will be reinitialized each time the block in which it is declared is entered.

...As mentioned earlier, Java also performs an automatic type conversion when storing a literal integer constant into variables of type byte, short, long, or char.


...Of course, if the size of the whole number component is too large to fit into the target integer type, then that value will be reduced modulo the target type’s range.


...To link month_days with an actual, physical array of integers, you must allocate one using new and assign it to month_days. new is a special operator that allocates memory.


You will look more closely at new in a later chapter, but you need to use it now to allocate memory for arrays.

...The elements in the array allocated by new will automatically be initialized to zero (for numeric types), false (for boolean), or null (for reference types, which are described in a later chapter).

...For example, if you need a very large two-dimensional array that is sparsely populated (that is, one in which not all of the elements will be used), then an irregular array might be a perfect solution.


...Thus, in principle, it would not be necessary to specify an explicit type for an initialized variable because it could be inferred by the type of its initializer.

...For example, in the past you would declare a local double variable called avg that is initialized with the value 10.0, as shown here:


...When it is used as the type name in the context of a local variable declaration, it tells the compiler to use type inference to determine the type of the variable being declared based on the type of the initializer.

...Only one variable can be declared at a time; a variable cannot use null as an initializer; and the variable being declared cannot be used by the initializer expression. 

...It also cannot be used as the name of other reference types, including an interface, enumeration, or annotation, or as the name of a generic type parameter, all of which are described later in this book.

...NOTE At the time of this writing, local variable type inference is quite new, and many readers of this book will be using Java environments that don’t support it. So that as many of the code examples as possible will compile and run for all readers, local variable type inference will not be used by most of the programs in the remainder of this edition of the book.