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Shyam Sunder Reddy
core java
1 Answer(s)      6 years and a month ago
Posted in : Java Interview Questions



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December 18, 2008 at 11:10 PM


Hi friend,


The purpose of the System class is to provide access to system resources.


The <CODE>System</CODE> class contains several useful class fields and methods. It cannot be instantiated. Among the facilities provided by the <CODE>System</CODE> class are standard input, standard output, and error output streams; access to externally defined properties and environment variables; a means of loading files and libraries; and a utility method for quickly copying a portion of an array.


Also known as static methods, these are any methods that are associated with a class, and not an object instance. There is always only one copy of a class method, regardless of the number of object instances that are created from that class. Class methods do not use the prototype object to implement inheritance. You access a class method directly through the class, and not through an object instance; you must define a class in a constructor function before you can define class methods.

The following example defines a function named setInitialSpeed() that can change the default speed of new car instances. The function name is assigned to the setInitialSpeed property of the Car class.

function Car(make, model, color) { // define a Car class
this.make = make;
this.model = model;
this.color = color;
this.speed = Car.defaultSpeed;
}
Car.defaultSpeed = 10; // initial speed for new Car instances
// increase the speed of a Car
function Car_setInitialSpeed(x) {
Car.defaultSpeed = x;
}
Car.setInitialSpeed = Car_setInitialSpeed;

You access the setInitialSpeed() class method directly from the Car class.

var newSpeed = Car.setInitialSpeed(30);

You can also create a class method by using function literal syntax. The following example uses function literal syntax to define a setInitialSpeed() method that contains the same functionality as the setInitialSpeed() function defined previously.

// increase the speed of a Car
Car.setInitialSpeed = function(x) {
Car.defaultSpeed = x;
}

-----------------------------------------

Read for more information.

http://www.roseindia.net/java/

Thanks.


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