Sams Teach Yourself C in 21 Days

Java Language Fundamentals 715

BD4

part of this line is a reference to Java’s error-handling mechanisms, which will be cov-

ered on Bonus Day 6. Line 10 declares a variable of type BufferedReader. I called this

variablekbbecause it will be used for keyboard input. Line 11 declares a variable of type

String, used in Java to hold text data (covered earlier today). Line 13 initializes kbso it

is ready for use. Line 14 displays a prompt on the screen. Line 15 reads a line of text

from the keyboard and stores it in s1. Finally, line 16 displays the entered text on the

screen.

There are more details of console input/output in Java, but the above techniques will

serve for the Java programs to be presented here.

Arrays ..................................................................................................................

As in C and C++, a Java array is an indexed method of storing data. Each element in an

array has the same name, and each is distinguished from the others by a numerical index.

For example, if you create an array called MyArray, and specify that it contains 100 type

intvariables, you would have MyArray[0],MyArray[1], up to MyArray[99]. An array

can hold either primitive data types or objects. There are two steps to creating an array in

Java. First, you must declare an identifier to reference the array. The syntax is

type ArrayIdentifier[];

Typeis the name of a class or a primitive data type, and ArrayIdentifieris the name of

the array. The empty brackets are what sets an array declaration apart from a regular

variable declaration. The second step creates the actual array and sets the array identifier

to reference it:

ArrayIdentifier = new type [elements];

Typeis the data type of the array and must be the same type as used in the identifier dec-

laration.Elementsis the number of elements in the array. The two steps for creating a

Java array can be combined in a single line of code:

type ArrayIdentifier = new type[elements];

If an array is a primitive data type or the Stringtype, you can start using it without any

further steps.

String Names = new String [50];

int Numbers = new int [100];

...

Names[1] = “Peter”;

Names[2] = “John”;

Numbers[1] = 2;

Numbers[2] = Numbers[1] + 5;

39 448201x-Bonus4 8/13/02 11:19 AM Page 715