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Section
1 :Declaration and Access Control
Write code that declares,
constructs, and initializes arrays of any base type
using any of the permitted forms both for declaration
and for initialization.
The declaration of an
array provides some information to the compiler such
as the type of the data the array will hold and its
name. To indicate that a variable of type array is
being declared, a pair of brackets is used. For
example:
float [] temperature ;
This statement does not
creates any array, it only creates a name, which can
be used to store reference to an array. The arrays are
implemented as objects in Java and hence the name of
the array does not stores the array, instead it stores
a reference to array.
If you wish to declare a
multi-dimensional array, you use more than one pair of
brackets.
float [][] temperature;
The size of the array is
indicated while creating the array using the
new operator.
temperature = new float [6];
Here an array is created
which would hold six items of type
float. This array will be
referred to by the name temperature. You can also use
any expression that evaluates to an integral type
except long at
runtime, to denote the size of the array. So, instead
of 6, you can write 2*3, or even an expression
containing variables whose values will be known only
at runtime. The value returned by the dimension
expression must be of integral type, or a compile time
error occurs. Each expression, undergoes unary numeric
promotion. The promoted type must be
int, or a compile time
error occurs. This means specifically that the type of
a dimension expression must not be
long .
These two statements are
generally combined in a single statement:
float [] temperature = new float [6];
Once an array is
created, its length never changes. To make an array
variable refer to an array of different length, a
reference to different array (which must be of the
same type) must be assigned to the variable. After
this array is created, its data can be accessed by
index values. The elements of an array are accessed by
using non negative integer index value. The first
element of an array is referred to as temperature [0],
since indexing in Java mostly begins with 0.
Unless all the elements
of an array are explicitly initialized, they are
initialized automatically with the default values of
the element type of the array. In the above example,
the default values of all the six items of data will
be 0.0, since it is the default value for
float.
To initialize an array,
each of the individual elements is initialized
separately.
temperature [0] = 34.6;
temperature [1] = 35.6; and so on.
Or you can use a loop to
initialize the elements of an array.
If the values of the
elements of an array are known at compile time, an
alternative way of declaring and initializing an array
can be used.
float [] temperature =
{34.6,35.6,36.6,37.5,32.9,30.8};
There is no restriction
on the order of pair of brackets and the variable
name. So, the following code is perfectly valid:
float temperature [] =
{34.6,35.6,36.6,37.5,32.9,30.8};
The component type of an
array may be one of the basic types such as
char, byte, short,
int,
long,
float,
double or
boolean, or it may be a
reference type. It may be an array itself.
While creating a
multidimensional array, dimensions must be created
left to right.
So,
int [] [] array = new
int [] [4]; is not valid.
section1-1 | section1-2 | section1-3 | section1-4
Sections :
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11
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