XML by Example

// ...

}

Creating Objects

Every object in Java is allocated on the heap. To create objects in Java, you

use the new operator.

1. The following example creates a

BufferedReader object:

BufferedReader reader =

new BufferedReader(new FileReader(args[0]));

2. Objects are typically assigned to variables, but they need not be. It is

also very common to create anonymous objects that are used and dis-

carded in one sequence. The following example creates a

File object,

calls its exists() method, and then discards it. The object is immedi-

ately discarded because it is never assigned to a variable:

if(new File(args[1]).exists())

System.err.println(“Error: output file already exists!”);

You don’t have to explicitly destroy objects in Java. When an object is no

longer in use, it is automatically reclaimed by the garbage collector.

Accessing Fields and Methods

A class contains fields or data variables that are attached to objects. It also

contains methods with the executable code of the class.

To access a field or a method of an object, you separate its name from the

object reference with a dot, as in

writer.close();

Static

By default, the variables or methods declared in a class are attached to

objects of that class. However, it is possible to declare variables or methods

attached to the class.

1. The following example declares a class with two fields:

x and y. Every

Point object has the two fields:

class Point

{

public int x, y;

}

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Appendix A

EXAMPLE

EXAMPLE

EXAMPLE

EXAMPLE