Perl教学(13)Perl地面向对象编制程序之五

Coffee.pm代码如下：

1 #
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 $this;
26 }
27 1;
第6行的require Bean;语句包含了Bean.pm文件和所有相关函数，方法setCoffeeType()用于设置局域变量$class->{'Coffee'}的值。在构造函数new()中，$this指向Bean.pm返回的匿名哈希表的指针，而不是在本地创建一个，下面两个语句分别为创建不同的哈希表从而与Bean.pm构造函数创建的哈希表无关的情况和继承的情况：
my $this = {}; #非继承
my $this = $theSuperClass->new(); #继承
下面代码演示如何调用继承的方法：

1 #!/usr/bin/perl
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";
该代码的结果输出如下：

-------------------- Initial values ------------
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
上述代码中，先输出对象创建时哈希表中索引为'Bean'和'Coffee'的值，然后调用各成员函数改变值后再输出。
方法可以有多个参数，现在向Coffee.pm模块增加函数makeCup()，代码如下：

sub makeCup {
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";
}
此函数可有三个参数，不同数目、值的参数产生不同的结果，例如：

1 #!/usr/bin/perl
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');
其结果输出如下：

Calling with no parameters:
==================================
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 ;-)
==================================
在此例中，函数makeCup()的参数既可为字符串也可为整数，处理结果相同，你也可以把这两种类型的数据处理区分开。在对参数的处理中，可以设置缺省的值，也可以根据实际输入参数值的个数给予不同处理。