This article describes how to properly redirect a web page using an HTTP 301 status code and Location header. The 301 status code is used to indicate that a page has permanently moved. Multiple techniques are presented with recommendations.
In order to redirect an out-of-print web page to another location, return the HTTP 301 status code and a location header in the HTTP response of the deprecated web page. The HTTP 301 response code will tell user-agents that the location has permanently moved. This is particularly useful for search engines like Google, which will carry over page rank to the new page if this status code is seen. If you do not need to indicate permanent displacement, you can accomplish redirection by setting a Location header in PHP or using Response.Redirect in ASP. The location header does the actual redirection to the new location, and can be used by itself.
HTTP headers are sent for every web page. If you want to see what HTTP headers look like for a particular page, visit Rex Swain's HTTP Viewer. For advanced users, I would recommend you download the Firefox web browser and install Chris Pederick's Web Developer Extensions. Then, use the Information->View Response Headers function. In scripts, HTTP headers must be sent before sending any page content, including white space, or else an error will result.
abstract means, hiding something. Here, hiding the complexity from user.
Q. Difference between an abstract class and an interface?
Abstract class is very similar to a general class only being difference is, we can instantiate it directly. We can use a abstract class only to inherit.
Interface will have only method signatures and final member variables and not the implementation. We can create an instance for an interface.
Q. Difference between overloading a method and overriding a method?
In method overloading, we will have same method name with each being accepting different parameters as input.
In overriding, the function signature remains same. But, the implementation changes. It can be seen in inheritance.
The rules for overriding a method are as follows:
- Theargument list must exactly matchthat of the overridden method.
- Thereturn type must exactly matchthat of the overridden method.
- Theaccesslevelmustnotbemorerestrictivethanthatoftheoverriddenmethod.
- Theaccess level can be less restrictivethan that of the overridden method.
- The overriding methodmust not throw new or broader checked exceptionsthan those declared by the overridden method.
- The overriding methodcan throw narrower or fewer exceptions. Just becausean overridden method “takes risks” doesn’t mean that the overriding subclass’exception takes the same risks. Bottom line: An overriding method doesn’thave to declare any exceptions that it will never throw, regardless of whatthe overridden method declares.
- Youcannot override a method markedfinal.
- If a method can’t be inherited, you cannot override it.
The rules for Overloaded method are as follows:
- Overloaded methodsmustchange the argument list.
- Overloaded methodscanchange the return type.
- Overloaded methodscanchange the access modifier.
- Overloaded methodscandeclare new or broader checked exceptions.
- A methodcanbe overloaded in the same class or in a subclass.
Overriding is the concept of runtime polymorphism while,
Overloading is the concept of compile time polymorphism...
Firefox, Opera, Safari: XMLHTTPRequest
IE: Msxml2.XMLHTTP (ActiveXObject)
2. Properties
onreadystatechange
readyState
0: the req is not initialized
1: the req has been set up
2: the req has been sent
3: the req is in process
4: the req is complete
responseText: the data sent back from server
3. Sending a request
Ajax uses open() and send() to send request to server. The open() takes 3 arguments:
- which method to use (GET or POST)
- URL of server-side script
- specifies that the request should be handled asynchronous (true or false)
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