Reference types - Data Structures and Problem Solving Using Java - page 37

String greeting = "hello";
int len = greeting.length( ); // len is 5
char ch = greeting.charAt( 1 ); // ch is 'e'
String sub = greeting.substring( 2, 4 ); // sub is "ll"

2.3.5 converting other types to strings

String concatenation provides a lazy way to convert any primitive to a String .
For instance, ""+45.3 returns the newly constructed String "45.3" . There are
also methods to do this directly.
The method toString can be used to convert any primitive type to a
String . As an example, Integer.toString(45) returns a reference to the newly
constructed String "45" . All reference types also provide an implementation
of toString of varying quality. In fact, when operator + has only one String
argument, the non String argument is converted to a String by automatically
applying an appropriate toString . For the integer types, an alternative form of
Integer.toString allows the specification of a radix. Thus

toString converts
primitive types (and
objects) to String s.

System.out.println( "55 in base 2: " + Integer.toString( 55, 2 ) );

prints out the binary representation of 55.
The int value that is represented by a String can be obtained by calling
the method Integer.parseInt . This method generates an exception if the
String does not represent an int . Exceptions are discussed in Section 2.5.
Similar ideas work for a double s. Here are some examples:

int x = Integer.parseInt( "75" );
double y = Double.parseDouble( "3.14" );

arrays

2.4

An aggregate is a collection of entities stored in one unit. An array is the
basic mechanism for storing a collection of identically typed entities. In Java
the array is not a primitive type. Instead, it behaves very much like an object.
Thus many of the rules for objects also apply to arrays.

An array stores a
collection of identi-
cally typed entities.

Each entity in the array can be accessed via the array indexing operator
[] . We say that the [] operator indexes the array, meaning that it specifies
which object is to be accessed. Unlike C and C++, bounds-checking is per-
formed automatically.
In Java, arrays are always indexed starting at zero. Thus an array a of three
items stores a[0] , a[1] , and a[2] . The number of items that can be stored in an

The array indexing
operator [] pro-
vides access to any
object in the array.