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This is illustrated by the program in Listing 5 . This program contains an overridden version of a superclass method named meth . The subclass version uses the value of an incoming parameter to decide whether to call thesuperclass version and then to call some of its own code, or to execute its own code exclusively.
| Listing 5 . The program named Super4 . |
|---|
/*File Super4.java
Copyright 2002, R.G.BaldwinIllustrates calling the superclass
version of an overridden method fromcode in the subclass version.
Tested using JDK 1.4.0 under Win 2000.The output from this program is:
In mainEntering overridden method in subclass
Incoming parameter is falseSubclass version only is called
Back in or still in subclass versionGoodbye from subclass version
Entering overridden method in subclassIncoming parameter is true
SuperClass method calledBack in or still in subclass version
Goodbye from subclass versionBack in main
**************************************/class SuperClass{
//Following method is overridden in// the subclass.
void meth(boolean par){System.out.println(
"Incoming parameter is " + par);System.out.println(
"SuperClass method called");}//end meth
}//end SuperClass class definition//===================================//
class Super4 extends SuperClass{//Following method overrides method
// in the superclassvoid meth(boolean par){
System.out.println("Entering overridden method "
+ "in subclass");//Decide whether to call
// superclass versionif(par)
//Call superclass versionsuper.meth(par);
else{//Don't call superclass version
System.out.println("Incoming parameter is " + par);
System.out.println("Subclass version only is "
+ "called");}//end else
//Execute some additional codeSystem.out.println(
"Back in or still in subclass "+ "version");
System.out.println("Goodbye from subclass version");
System.out.println();//blank line}//end overridden meth()
//---------------------------------//public static void main(
String[]args){
//instantiate an object of// this type
Super4 obj = new Super4();System.out.println("In main");
//Call overridden version of// method
obj.meth(false);//Call superclass version of
// methodobj.meth(true);
System.out.println("Back in main");}//end main method
}//End Super4 class definition. |
Only one statement contains super
The super keyword is used in only one statement in the program in Listing 5 . That statement appears in the subclass version of an overridden method, and is as follows:
super.meth(par);
This statement is inside the body of an if statement. If the value of par is true, then this statement is executed, causing the superclass version of the method named meth to be executed (passing the value of par as a parameter to the superclass method). When the method returns, the remaining code in the subclass version of the method is executed.
If the value of par is false, the above statement is bypassed, and the superclass version of the method doesn't get executed. In this case, only thecode in the subclass version is executed.
I have discussed and illustrated the use of the this keyword in the following common situations:
I have also discussed and illustrated the use of the super keyword in the following situations:
The next module in this collection will teach you how to use exception handling in Java.
This section contains a variety of miscellaneous information.
Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.
I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.
In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.
Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.
-end-
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