Java 4android video learning notes-object-oriented applications (I), java object-oriented notes

Java 4android video learning notes-object-oriented applications (I), java object-oriented notes

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There is an HP printer that requires a program to enable boot, printing, and shutdown.

 

Class HPprinter {void open () {System. out. println ("Open");} void print (String s) {System. out. println ("print -->" + s);} void close () {System. out. println ("Close ");}}

 

 

 

Class Test {public static void main (String args []) {HPprinter hp = new HPprinter (); hp. open (); hp. print ("abc"); hp. close ();}}

 

Later, a Canon printer needs to be turned on, printed, cleaned, and shut down.

 

Class Canonprinter
{
Void open (){
System. out. println ("Open ");
}


Void print (String s ){
System. out. println ("print -->" + s );
}

Void close (){
This. clean ();
System. out. println ("Close ");
}

Void clean (){
System. out. println ("Clean ");
}
}

 

How can we use the same program to implement the functions of the two printers?

Class Test
{
Public static void main (String args [])
{
Int a = 0;


HPprinter hp = new HPprinter ();
Canonprinter canon = new Canonprinter ();


If (a = 1) {// note that an equal sign must be used here.
Hp. open ();
Hp. print ("abc ");
Hp. close ();
}

Else if (a = 0 ){
Canon. open ();
Canon. print ("123 ");
Canon. close ();
}

}
}

 

The above program has a lot of repeated code. If there are a lot of different printers to add, it is easy to change a program, it is also easy to change two programs, it is always impossible to change each program again? In fact, we can minimize the risk and eliminate the repeated code.

Create a parent Printer

Class Printer
{
Void open (){
System. out. println ("Open ");
}


Void print (String s ){
System. out. println ("Print -->" + s );
}


Void close (){
System. out. println ("Close ");
}
}

Inherit all types of printers

Class HPprinter extends Printer
{

}

 

Class Canonprinter extends Printer
{
Void close (){
This. clean ();
Super. close ();
}

Void clean (){
System. out. println ("Clean ");
}
}

Main Function

Class Test
{
Public static void main (String args [])
{
Int a = 0;

HPprinter hp = new HPprinter ();
Canonprinter canon = new Canonprinter ();

If (a = 1 ){
Hp. open ();
Hp. print ("abc ");
Hp. close ();
}

Else if (a = 0 ){
Canon. open ();
Canon. print ("123 ");
Canon. close ();
}

}
}

 

 

So far

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