第十三章 Perl的面向?qū)ο缶幊?/p>
一、模塊簡(jiǎn)介package Cocoa;接下來(lái)，我們往包里添加方法使之成為一個(gè)類。第一個(gè)需添加的方法是new()，它是創(chuàng)建對(duì)象時(shí)必須被調(diào)用的，new()方法是對(duì)象的構(gòu)造函數(shù)。
#
# Put "require" statements in for all required,imported packages
#
#
# Just add code here
#
1; # terminate the package with the required 1;
sub new {{}創(chuàng)建一個(gè)對(duì)不含鍵/值對(duì)的哈希表（即關(guān)聯(lián)數(shù)組）的引用，返回值被賦給局域變量$this。函數(shù)bless()取出該引用，告訴對(duì)象它引用的是Cocoa，最后返回該引用。函數(shù)的返回值現(xiàn)在指向這個(gè)匿名哈希表。
my $this = {}; # Create an anonymous hash, and #self points to it.
bless $this; # Connect the hash to the package Cocoa.
return $this; # Return the reference to the hash.
}
1;
1 #!/usr/bin/perl第一行指出Perl解釋器的位置，第二行中，將當(dāng)前目錄加到路徑尋找列表@INC中供尋找包時(shí)使用。你也可以在不同的目錄中創(chuàng)建你的模塊并指出該絕對(duì)路徑。例如，如果在/home/test/scripts/創(chuàng)建包，第二行就應(yīng)該如下：
2 push (@INC,'pwd');
3 use Cocoa;
4 $cup = new Cocoa;
1、一定要在構(gòu)造函數(shù)中初始化變量；加上聲明的Cocoa構(gòu)造函數(shù)如下：
2、一定要用my函數(shù)在方法中創(chuàng)建變量；
3、一定不要在方法中使用local，除非真的想把變量傳遞給其它子程序；
4、一定不要在類模塊中使用全局變量。
sub new {也可以簡(jiǎn)單地調(diào)用包內(nèi)或包外的其它函數(shù)來(lái)做更多的初始化工作，如：
my $this = {};
print "\n /* \n ** Created by Cocoa.pm \n ** Use at own risk";
print "\n ** Did this code even get pass the javac compiler? ";
print "\n **/ \n";
bless $this;
return $this;
}
sub new {創(chuàng)建類時(shí)，應(yīng)該允許它可被繼承，應(yīng)該可以把類名作為第一個(gè)參數(shù)來(lái)調(diào)用new函數(shù)，那么new函數(shù)就象下面的語(yǔ)句：
my $this = {}
bless $this;
$this->doInitialization();
return $this;
}
sub new {此方法使用戶可以下列三種方式之一來(lái)進(jìn)行調(diào)用：
my $class = shift; # Get the request class name
my $this = {};
bless $this, $class # Use class name to bless() reference
$this->doInitialization(); return $this;
}
可以多次bless一個(gè)引用對(duì)象，然而，新的將被bless的類必然把對(duì)象已被bless的引用去掉，對(duì)C和Pascal程序員來(lái)說(shuō)，這就象把一個(gè)指針賦給分配的一塊內(nèi)存，再把同一指針賦給另一塊內(nèi)存而不釋放掉前一塊內(nèi)存。總之，一個(gè)Perl對(duì)象每一時(shí)刻只能屬于一個(gè)類。Cocoa::new() Cocoa->new() new Cocoa
sub new {用數(shù)組保存的代碼如下：my $type = shift;}
my %parm = @_;
my $this = {};
$this->{'Name'} = $parm{'Name'};
$this->{'x'} = $parm{'x'};
$this->{'y'} = $parm{'y'};
bless $this, $type;
sub new {構(gòu)造對(duì)象時(shí)，可以如下傳遞參數(shù)：my $type = shift;}
my %parm = @_;
my $this = [];
$this->[0] = $parm{'Name'};
$this->[1] = $parm{'x'};
$this->[2] = $parm{'y'};
bless $this, $type;
1. sub nameLister {六、方法的輸出
2. my $this = shift;
3. my ($keys ,$value );
4. while (($key, $value) = each (%$this)) {
5. print "\t$key is $value.\n";
6. }
7. }
package Cocoa;現(xiàn)在，我們寫(xiě)一個(gè)簡(jiǎn)單的Perl腳本來(lái)使用該類的方法，下面是創(chuàng)建一個(gè)Java applet源代碼骨架的腳本代碼：
require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(setImports, declareMain, closeMain);
#
# This routine creates the references for imports in Java functions
#
sub setImports{
my $class = shift @_;
my @names = @_;
foreach (@names) {
print "import " . $_ . ";\n";
}
}
#
# This routine declares the main function in a Java script
#
sub declareMain{
my $class = shift @_;
my ( $name, $extends, $implements) = @_;
print "\n public class $name";
if ($extends) {
print " extends " . $extends;
}
if ($implements) {
print " implements " . $implements;
}
print " { \n";
}
#
# This routine declares the main function in a Java script
#
sub closeMain{
print "} \n";
}
#
# This subroutine creates the header for the file.
#
sub new {
my $this = {};
print "\n /* \n ** Created by Cocoa.pm \n ** Use at own risk \n */ \n";
bless $this;
return $this;
}
1;
#!/usr/bin/perl這段腳本創(chuàng)建了一個(gè)叫做Msg的Java applet，它擴(kuò)展(extend)了java.applet.Applet小應(yīng)用程序并使之可運(yùn)行(runnable)，其中最后三行也可以寫(xiě)成如下：
use Cocoa;
$cup = new Cocoa;
$cup->setImports( 'java.io.InputStream', 'java.net.*');
$cup->declareMain( "Msg" , "java.applet.Applet", "Runnable");
$cup->closeMain();
Cocoa::setImports($cup, 'java.io.InputStream', 'java.net.*');其運(yùn)行結(jié)果如下：
Cocoa::declareMain($cup, "Msg" , "java.applet.Applet", "Runnable");
Cocoa::closeMain($cup);
/*注意：如果用->操作符調(diào)用方法（也叫間接調(diào)用），參數(shù)必須用括號(hào)括起來(lái)，如：$cup->setImports( 'java.io.InputStream', 'java.net.*');而雙冒號(hào)調(diào)用如：Cocoa::setImports($cup, 'java.io.InputStream', 'java.net.*');也可去掉括號(hào)寫(xiě)成：Cocoa::setImports $cup, 'java.io.InputStream', 'java.net.*' ;
** Created by Cocoa.pm
** Use at own risk
*/
import java.io.InputStream;
import java.net.*;
public class Msg extends java.applet.Applet implements Runnable {
}
sub DESTROY {因?yàn)槎喾N目的，Perl使用了簡(jiǎn)單的、基于引用的垃圾回收系統(tǒng)。任何對(duì)象的引用數(shù)目必須大于零，否則該對(duì)象的內(nèi)存就被釋放。當(dāng)程序退出時(shí)，Perl的一個(gè)徹底的查找并銷毀函數(shù)進(jìn)行垃圾回收，進(jìn)程中的一切被簡(jiǎn)單地刪除。在UNIX類的系統(tǒng)中，這像是多余的，但在內(nèi)嵌式系統(tǒng)或多線程環(huán)境中這確實(shí)很必要。
#
# Add code here.
#
}
package Bean;此類中，用$this變量設(shè)置一個(gè)匿名哈希表，將'Bean'類型設(shè)為'Colombian'。方法setBeanType()用于改變'Bean'類型，它使用$class引用獲得對(duì)對(duì)象哈希表的訪問(wèn)。
require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(setBeanType);
sub new {
my $type = shift;
my $this = {};
$this->{'Bean'} = 'Colombian';
bless $this, $type;
return $this;
}
#
# This subroutine sets the class name
sub setBeanType{
my ($class, $name) = @_;
$class->{'Bean'} = $name;
print "Set bean to $name \n";
}
1;
1 #第6行的require Bean;語(yǔ)句包含了Bean.pm文件和所有相關(guān)函數(shù)，方法setCoffeeType()用于設(shè)置局域變量$class->{'Coffee'}的值。在構(gòu)造函數(shù)new()中，$this指向Bean.pm返回的匿名哈希表的指針，而不是在本地創(chuàng)建一個(gè)，下面兩個(gè)語(yǔ)句分別為創(chuàng)建不同的哈希表從而與Bean.pm構(gòu)造函數(shù)創(chuàng)建的哈希表無(wú)關(guān)的情況和繼承的情況：
2 # The Coffee.pm file to illustrate inheritance.
3 #
4 package Coffee;
5 require Exporter;
6 require Bean;
7 @ISA = qw(Exporter, Bean);
8 @EXPORT = qw(setImports, declareMain, closeMain);
9 #
10 # set item
11 #
12 sub setCoffeeType{
13 my ($class,$name) = @_;
14 $class->{'Coffee'} = $name;
15 print "Set coffee type to $name \n";
16 }
17 #
18 # constructor
19 #
20 sub new {
21 my $type = shift;
22 my $this = Bean->new(); ##### <- LOOK HERE!!! ####
23 $this->{'Coffee'} = 'Instant'; # unless told otherwise
24 bless $this, $type;
25 return $this;
26 }
27 1;
1 #!/usr/bin/perl該代碼的結(jié)果輸出如下：
2 push (@INC,'pwd');
3 use Coffee;
4 $cup = new Coffee;
5 print "\n -------------------- Initial values ------------ \n";
6 print "Coffee: $cup->{'Coffee'} \n";
7 print "Bean: $cup->{'Bean'} \n";
8 print "\n -------------------- Change Bean Type ---------- \n";
9 $cup->setBeanType('Mixed');
10 print "Bean Type is now $cup->{'Bean'} \n";
11 print "\n ------------------ Change Coffee Type ---------- \n";
12 $cup->setCoffeeType('Instant');
13 print "Type of coffee: $cup->{'Coffee'} \n";
-------------------- Initial values ------------上述代碼中，先輸出對(duì)象創(chuàng)建時(shí)哈希表中索引為'Bean'和'Coffee'的值，然后調(diào)用各成員函數(shù)改變值后再輸出。
Coffee: Instant
Bean: Colombian
-------------------- Change Bean Type ----------
Set bean to Mixed
Bean Type is now Mixed
------------------ Change Coffee Type ----------
Set coffee type to Instant
Type of coffee: Instant
sub makeCup {此函數(shù)可有三個(gè)參數(shù)，不同數(shù)目、值的參數(shù)產(chǎn)生不同的結(jié)果，例如：
my ($class, $cream, $sugar, $dope) = @_;
print "\n================================== \n";
print "Making a cup \n";
print "Add cream \n" if ($cream);
print "Add $sugar sugar cubes\n" if ($sugar);
print "Making some really addictive coffee ;-) \n" if ($dope);
print "================================== \n";
}
1 #!/usr/bin/perl其結(jié)果輸出如下：
2 push (@INC,'pwd');
3 use Coffee;
4 $cup = new Coffee;
5 #
6 # With no parameters
7 #
8 print "\n Calling with no parameters: \n";
9 $cup->makeCup;
10 #
11 # With one parameter
12 #
13 print "\n Calling with one parameter: \n";
14 $cup->makeCup('1');
15 #
16 # With two parameters
17 #
18 print "\n Calling with two parameters: \n";
19 $cup->makeCup(1,'2');
20 #
21 # With all three parameters
22 #
23 print "\n Calling with three parameters: \n";
24 $cup->makeCup('1',3,'1');
Calling with no parameters:在此例中，函數(shù)makeCup()的參數(shù)既可為字符串也可為整數(shù)，處理結(jié)果相同，你也可以把這兩種類型的數(shù)據(jù)處理區(qū)分開(kāi)。在對(duì)參數(shù)的處理中，可以設(shè)置缺省的值，也可以根據(jù)實(shí)際輸入?yún)?shù)值的個(gè)數(shù)給予不同處理。
==================================
Making a cup
==================================
Calling with one parameter:
==================================
Making a cup
Add cream
==================================
Calling with two parameters:
==================================
Making a cup
Add cream
Add 2 sugar cubes
==================================
Calling with three parameters:
==================================
Making a cup
Add cream
Add 3 sugar cubes
Making some really addictive coffee ;-)
==================================
sub printType {然后更新其@EXPORT數(shù)組來(lái)輸出：
my $class = shift @_;
print "The type of Bean is $class->{'Bean'} \n";
}
$cup->Coffee::printType();輸出分別如下：
$cup->printType();
$cup->Bean::printType();
The type of Bean is Mixed為什么都一樣呢？因?yàn)樵谧宇愔袥](méi)有定義函數(shù)printType()，所以實(shí)際均調(diào)用了基類中的方法。如果想使子類有其自己的printType()函數(shù)，必須在Coffee.pm類中加以定義：
The type of Bean is Mixed
The type of Bean is Mixed
#然后更新其@EXPORT數(shù)組：
# This routine prints the type of $class->{'Coffee'}
#
sub printType {
my $class = shift @_;
print "The type of Coffee is $class->{'Coffee'} \n";
}
The type of Coffee is Instant現(xiàn)在只有當(dāng)給定了Bean::時(shí)才調(diào)用基類的方法，否則直接調(diào)用子類的方法。
The type of Coffee is Instant
The type of Bean is Mixed
The type of Bean is Mixed十二、Perl類和對(duì)象的一些注釋
1、一定要通過(guò)方法來(lái)訪問(wèn)類變量。當(dāng)編寫(xiě)包時(shí)，應(yīng)該保證方法所需的條件已具備或通過(guò)參數(shù)傳遞給它。在包內(nèi)部，應(yīng)保證對(duì)全局變量的訪問(wèn)只用通過(guò)方法傳遞的引用來(lái)訪問(wèn)。對(duì)于方法要使用的靜態(tài)或全局?jǐn)?shù)據(jù)，應(yīng)該在基類中用local()來(lái)定義，子類通過(guò)調(diào)用基類來(lái)獲取。有時(shí)，子類可能需要改變這種數(shù)據(jù)，這時(shí)，基類可能就不知道怎樣去尋找新的數(shù)據(jù)，因此，這時(shí)最好定義對(duì)該數(shù)據(jù)的引用，子類和基類都通過(guò)引用來(lái)改變?cè)摂?shù)據(jù)。
2、一定不要從模塊外部直接訪問(wèn)類變量。