Java Reference
In-Depth Information
Java syntax: Subscripted variable
array [ int - expression ]
Examples : b[5]= b[4] + 2;
Purpose : To access an array element, to either retrieve its
value (as in b[4] ) or change it (above, b[5] is changed).
the value 2 in b[2] is called the subscript , or index , of the array element. We call
b[2] a subscripted variable.
The range of an array is the set of values that can be used as indices. The
range of b consists of 0 , 1 , 2 , and 3 ; we write this range as 0..3 .
The following statement stores the sum of b[0] and b[1] in variable b[3] :
b[3]= b[0] + b[1];
Any int expression can be used as an index. For example, if an int variable
x has the value 5 , b[x - 4] refers to subscripted variable b[1] .
Declarations of arrays
Below, we show a declaration of an array:
int [] b;
The notation int [] is read as “ int array”, and b 's type is int [] . Arrays are
objects. Just as the declaration:
String s;
does not create a String object, b 's declaration does not create an array object.
It merely declares that variable b can contain the name of an int array object.
Type int is called the base type of the array. Any type can be used as the
base type. Here is a declaration for an array of strings:
String[] s;
Creating an array
To create an array object and assign it to b , use a new-expression in an assign-
ment statement. The new-expression syntax is slightly different from other new-
expressions; no constructor is called. Here is an example:
b= new int [4];
Common error . When using a subscripted variable b[i] , the value of i must be within the range
of b —one of the values in 0..b.length - 1 . If i is not in range, an IndexOut-
OfBoundsException occurs and execution aborts. Get in the habit of always
asking yourself, with each variable b[i] you write, whether i is within range.
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