设计模式之适配器-典型代码分析

class Customer {
public static final String US = "US";
public static final String CANADA = "Canada";
private String address;
private String name;
private String zip, state, type;
public boolean isValidAddress() {
…
…
}
public Customer(String inp_name, String inp_address,
String inp_zip, String inp_state,
String inp_type) {
name = inp_name;
address = inp_address;
zip = inp_zip;
state = inp_state;
type = inp_type;
}
}//end of class

不同的客户对象创建Customer对象并调用（invoke）isValidAddress方法验证客户地址的有效性。为了验证客户地址的有效性，Customer类期望利用一个地址验证类（address validator class），这个验证类提供了在接口AddressValidator中声明的接口。
Listing 20.2: AddressValidator as an Interface

public interface AddressValidator {
public boolean isValidAddress(String inp_address,
String inp_zip, String inp_state);
}//end of class

　 让我们定义一个USAddress的验证类，来验证给定的U.S地址。
Listing 20.3: USAddress Class

class USAddress implements AddressValidator {
public boolean isValidAddress(String inp_address,
String inp_zip, String inp_state) {
if (inp_address.trim().length() < 10)
return false;
if (inp_zip.trim().length() < 5)
return false;
if (inp_zip.trim().length() > 10)
return false;
if (inp_state.trim().length() != 2)
return false;
return true;
}
}//end of class

　USAddress类实现AddressValidator接口，因此Customer对象使用USAddress实例作为验证客户地址过程的一部分是没有任何问题的。
Listing 20.4: Customer Class Using the USAddress Class

class Customer {
…
…
public boolean isValidAddress() {
//get an appropriate address validator
AddressValidator validator = getValidator(type);
//Polymorphic call to validate the address
return validator.isValidAddress(address, zip, state);
}
private AddressValidator getValidator(String custType) {
AddressValidator validator = null;
if (custType.equals(Customer.US)) {
validator = new USAddress();
}
return validator;
}
}//end of class