编写问题域类定义.ppt

第5章 编写问题域类定义,课程回顾 UML 三层设计,第5章 编写问题域类定义,开发PD类定义 测试PD类 编写构造函数方法 编写toString方法 为Slip类编写定义 编写自定义方法 格式化输出 使用静态变量和静态方法 重载方法 处理异常,第5章 编写问题域类定义,编写规范 类名：大写字母开头，Customer 属性名：小写字母开头，但后面的字可用大写字母，phoneNo 方法名：动词在前，名次在后，小写字母开头，setAddress,第5章 编写问题域类定义,首先以客户类为例子 定义Customer类 定义属性： private String name; private String address; private String phoneNo; 定义方法：get方法，set方法。,5.1 开发PD类定义,5.1 开发PD类定义,Java类的结构定义,public class Customer / attribute definitions private String name; private String address; private String phoneNo; / get方法 public String getName() return name; public String getAddress() return address; public String getPhoneNo() return phoneNo;,5.1 开发PD类定义,/ set方法 public void setName(String newName) name = newName; public void setAddress(String newAddress) address = newAddress; public void setPhoneNo(String newPhoneNo) phoneNo = newPhoneNo; ,5.1 开发PD类定义,5.1 开发PD类定义,public class TesterOne public static void main(String args) Customer firstCustomer = new Customer(); / create instance / invoke set accessors to populate attributes firstCustomer.setName(Eleanor); firstCustomer.setAddress(Atlanta); firstCustomer.setPhoneNo(123-4567); / define variables to contain attribute values retrieved String customerName, customerAddress, customerPhoneNo;,5.2 测试PD类,/ invoke get accessors to retrieve attribute values customerName = firstCustomer.getName(); customerAddress = firstCustomer.getAddress(); customerPhoneNo = firstCustomer.getPhoneNo(); / display the retrieved attribute values System.out.println(The name is + customerName); System.out.println(The address is + customerAddress); System.out.println(The phone is + customerPhoneNo); ,5.2 测试PD类,TesterOne序列图,5.2 测试PD类,创建多个实例？,5.2 测试PD类,构造方法：默认的构造方法，自定义构造方法。 默认的构造方法仅由头和一个空的代码块组成。 Public Customer() ,5.3 编写构造方法,自定义构造函数（参数化的构造函数）： public Customer(String aName, String anAddress, String aPhoneNo) / invoke setters to populate attributes this.name = aName; address = anAddress; phoneNo = aPhoneNo; ,5.3 编写构造方法,创建多个实例： 姓名： Eleanor Mike JoAnn 地址： Atlanta Boston St.Louis 电话号码：123-4567 456-1234 765-4321,5.3 编写构造方法,编写TesterThree类对Customer类中的构造函数方法进行测试： public class TesterThree public static void main(String args) / define the reference variables Customer firstCustomer, secondCustomer, thirdCustomer; / create three Customer instances with attribute values firstCustomer = new Customer(Eleanor, Atlanta, 123-4567); secondCustomer = new Customer(Mike, Boston, 467-1234); thirdCustomer = new Customer(JoAnn, St. Louis, 765-4321); / retrieve ,5.3 编写构造方法,作用：检索实例所有的属性值，将它们置于一个String对象中。 public String toString() String info; info = Customer name = + getName() + , Address = + getAddress() + , Phone Number = + getPhoneNo(); return info; ,5.4 编写toString方法,public class TesterFour public static void main(String args) / define the reference variables Customer firstCustomer, secondCustomer, thirdCustomer; / create three Customer instances with attribute values firstCustomer = new Customer(Eleanor, Atlanta, 123-4567); secondCustomer = new Customer(Mike, Boston, 467-1234); thirdCustomer = new Customer(JoAnn, St. Louis, 765-4321); / invoke tellAbutSelf for all three customers ,5.4 编写toString方法,Slip slipId width slipLength,5.5 为Slip类编写定义,Slip类的类图,public class Slip / attributes private int slipId; private int width; private double slipLength; / constructor with 3 parameters public Slip(int anId, int aWidth, double aSlipLength) / invoke setters to populate attributes setSlipId(anId); setWidth(aWidth); setSlipLength(aSlipLength); ,5.5 为Slip类编写定义,/ set methods public void setSlipId(int anId) slipId = anId; public void setWidth(int aWidth) width = aWidth; public void setSlipLength(double aSlipLength) slipLength = aSlipLength; / get methods public int getSlipId() return slipId; public int getWidth() return width; public double getSlipLength() return slipLength;,5.5 为Slip类编写定义,/ custom method toString public String toString() String info; info = Slip: Id = + getSlipId() + , Width = + getWidth() + , Length = + getSlipLength(); return info; ,5.5 为Slip类编写定义,编写tester类（TestOne）来测试代码的正确性： TestOne 类仅有一个单一方法main, 在mian中定义具有三个元素的数组slips来保存Slip实例。 Slip slips = new Slip3; / 构造函数的三个参数分别表示slipId, width, slipLength。 Slips0 = new Slip(1,10,20); Slips1 = new Slip(2,12,25); Slips2 = new Slip(3,14,30);,5.5 为Slip类编写定义,public class TesterOne public static void main(String args) / create an array to hold three Slip references Slip slips = new Slip3; / create 3 Slip instances slips0 = new Slip(1, 10, 20); slips1= new Slip(2, 12, 25); slips2= new Slip(3, 14, 30); / retrieve ,5.5 为Slip类编写定义,5.5 为Slip类编写定义,Slip: Id = 1, Width = 10, Length = 20.0 Slip: Id = 2, Width = 12, Length = 25.0 Slip: Id = 3, Width = 14, Length = 30.0 Press any key to continue.,5.5 为Slip类编写定义,编写自定义方法leaseSlip，计算船台的出租费用。 出租费用： 船台宽度 年租金 10 $800 12 $900 14 $1100 16 $1500,5.6 编写自定义方法,/ custom method to lease a Slip public double leaseSlip() double fee; switch(width) case 10: fee = 800; break; case 12: fee = 900; break; case 14: fee = 1100; break; case 16: fee = 1500; break; default: fee = 0; return fee; ,5.6 编写自定义方法,public class TesterTwo public static void main(String args) / create an array to hold three Slip references Slip slips = new Slip3; / create 3 Slip instances slips0 = new Slip(1, 10, 20); slips1= new Slip(2, 12, 25); slips2= new Slip(3, 14, 30); / compute ,5.6 编写自定义方法,Fee is 800.0 for slip 1 Fee is 900.0 for slip 2 Fee is 1100.0 for slip 3 Press any key to continue.,5.6 编写自定义方法,使用NumberFormat和DecimalFormat（在java.text包中）： NumberFormat类提供将数字数据作为货币（带有逗号,货币符号和小数点）进行格式化的方法，以及不同国家格式化货币的方法。 使用DecimalFormat类对带有逗号和小数点，但未带有美元符号的数字进行格式化。,5.7 格式化输出,Class NumberFormat java.lang.Object | +-java.text.Format | +- 在使用NumberFormat类之前，需要使用import语句： import java.text.*;,java.text.NumberFormat,5.7 格式化输出,public abstract class NumberFormat extends Format 静态方法：getInstance public static final NumberFormat getInstance(),5.7 格式化输出,使用getInstance方法，格式化数据： NumberFormat general = NumberFormat.getInstance(); myString = general.format(myNumber); 格式化多个数据： NumberFormat nf = NumberFormat.getInstance(); for (int i = 0; i a.length; +i) System.out.println(nf.format(myNumberi) + ; ); ,5.7 格式化输出,import java.text.*; public class TesterThree public static void main(String args) / create a Slip instance Slip aSlip = new Slip(3, 14, 30); / compute lease fee double fee = aSlip.leaseSlip(); System.out.println(fee); / illustrate number format NumberFormat nf = NumberFormat.getInstance(); System.out.println(number: + nf.format(fee); ,5.7 格式化输出,1100.0 number: 1,100 Press any key to continue.,5.7 格式化输出,getCurrencyInstance 方法： public static final NumberFormat getCurrencyInstance() /Returns a currency format for the current default locale. public static NumberFormat getCurrencyInstance(LocaleinLocale) /Returns a currency format for the specified locale.,5.7 格式化输出,import java.text.*; import java.util.*; public class TesterThree public static void main(String args) / create a Slip instance Slip aSlip = new Slip(3, 14, 30); / compute lease fee double fee = aSlip.leaseSlip(); / illustrate currency format NumberFormat currencyFormat = NumberFormat.getCurrencyInstance(); System.out.println(Currency: + currencyFormat.format(fee); NumberFormat ccFormat = NumberFormat. getCurrencyInstance(Locale.US); System.out.println(Currency: + ccFormat.format(fee); ,5.7 格式化输出,Currency: ￥1,100.00 Currency: $1,100.00 Press any key to continue.,5.7 格式化输出,java.text Class DecimalFormat java.lang.Object | +-java.text.Format | +- java.text.NumberFormat | +- java.text.DecimalFormat,5.7 格式化输出,public class DecimalFormat extends NumberFormat /DecimalFormat is a concrete subclass of NumberFormat that formats decimal numbers. It also supports different kinds of numbers, including integers (123), fixed-point numbers (123.4), scientific notation (1.23E4), percentages (12%).,5.7 格式化输出,DecimalFormat d1Format = new DecimalFormat(#,#0.00); #要显示的数字保留位置，会取消所有的前导零 0强制显示某个字符，即使字符的值为零,5.7 格式化输出,import java.text.*; import java.util.*; public class TesterThree public static void main(String args) / create a Slip instance Slip aSlip = new Slip(3, 14, 30); double fee = aSlip.leaseSlip(); DecimalFormat d1Format = new DecimalFormat(#,#0.00); System.out.println(Decimal: + d1Format.format(fee); DecimalFormat d2Format = new DecimalFormat(#,#0.00); System.out.println(Decimal: + d2Format.format(fee); DecimalFormat d3Format = new DecimalFormat(00000.00); System.out.println(Decimal: + d3Format.format(fee); ,5.7 格式化输出,Decimal: 1,100.00 Decimal: 11,00.00 Decimal: 01100.00 Press any key to continue.,5.7 格式化输出,使用换码顺序: n (newline) b (backspace) f (form feed ) (single quote) t (tab) r (return) (backslash) (double quote),5.7 格式化输出,import java.text.*; public class TesterThree public static void main(String args) / create a Slip instance Slip aSlip = new Slip(3, 14, 30); / compute lease fee double fee = aSlip.leaseSlip(); / illustrate escape sequences System.out.println(Before tab t after tab); System.out.println(Before new line n after new line); System.out.println(Display double quote ); ,5.7 格式化输出,Before tab after tab Before new line after new line Display double quote Press any key to continue.,5.7 格式化输出,静态变量:类变量； 静态方法:类方法； 关键字：static 所有实例共享，每个实例没有自己的副本,5.8 使用静态变量和静态方法,在Slip类中加入静态变量船台数量： private static int numberofSlips = 0; 在Slip类的构造函数中增加下面的语句： numberofSlips+; 编写getter方法返回numberofSlips的内容： public static int getNumberofSlips() return getNumberofSlips; ,5.8 使用静态变量和静态方法,public class Slip / attributes private int slipId; private int width; private double slipLength; / static attribute variable private static int numberOfSlips = 0; / constructor with 3 parameters public Slip(int anId, int aWidth, double aSlipLength) / invoke setters to populate attributes setSlipId(anId); setWidth(aWidth); setSlipLength(aSlipLength); numberOfSlips+; ,5.8 使用静态变量和静态方法,/ custom method to lease a Slip public double leaseSlip() double fee; switch(width) case 10: fee = 800; break; case 12: fee = 900; break; case 14: fee = 1100; break; case 16: fee = 1500; break; default: fee = 0; return fee; ,5.8 使用静态变量和静态方法,/ setters public void setSlipId(int anId) slipId = anId; public void setWidth(int aWidth) width = aWidth; public void setSlipLength(double aSlipLength) slipLength = aSlipLength; / getters public int getSlipId() return slipId; public int getWidth() return width; public double getSlipLength() return slipLength; / static method public static int getNumberOfSlips() return numberOfSlips;,5.8 使用静态变量和静态方法,/ toString public String toString() String info; info = Slip: Id = + getSlipId() + , Width = + getWidth() + , Length = + getSlipLength(); return info; ,5.8 使用静态变量和静态方法,public class TesterFour public static void main(String args) Slip slips = new Slip3; slips0 = new Slip(1, 10, 20); System.out.println(Number of slips + Slip.getNumberOfSlips(); slips1= new Slip(2, 12, 25); System.out.println(Number of slips + Slip.getNumberOfSlips(); slips2= new Slip(3, 14, 30); System.out.println(Number of slips + Slip.getNumberOfSlips(); / retrieve ,5.8 使用静态变量和静态方法,Number of slips 1 Number of slips 2 Number of slips 3 Number of slips (ref var) 3 Press any key to continue.,5.8 使用静态变量和静态方法,方法签名(method signature)包括方法名及参数表 Java通过签名来识别方法。 方法重载（ overloaded method ）：在一个类中可以定义多个方法，它们具有相同的方法名及不同的参数表。,5.9 重载方法,与多态的区别： 多态：当一个类中的某方法与第二个类中的某方法具有相同签名 重载：同一个类中有两个以上相同的方法名，但是参数表不同,5.9 重载方法,重载构造函数,有时需要多个构造函数，每一个构造函数有不同的参数表。 大多数船台有12英尺宽、25英尺长，但少数及个船台具有不同的宽度和长度。 目前的 Slip 构造函数需要3个实参：slipId, width ， slipLength.,5.9 重载方法,改进：增加第二个构造函数，只有slipId一个形参。 另外两项使用默认值： 12 feet wide and 25 feet long.,5.9 重载方法,此外，为了方便以后代码维护，设置静态常量 private static final int DEFAULT_WIDTH = 12; private static final int DEFAULT_SLIP_LENGTH = 25;,5.9 重载方法,第二个构造函数方法除了只有一个形参用来接收船台ID值。 public Slip(int anId) / invoke 3-parameter constructor with default width ,5.9 重载方法,public class TesterFive public static void main(String args) / create 2 Slip instances using different constructors / first use original constructor passing 3 arguments Slip firstSlip = new Slip(1, 10, 20); / next, use 2nd constructor passing only 1 argument Slip secondSlip = new Slip(2); / retrieve ,5.9 重载方法,Slip: Id = 1, Width = 10, Length = 20.0 Slip: Id = 2, Width = 12, Length = 25.0,5.9 重载方法,重载自定义方法,如在特殊情况下，允许将租金打折。 编写leaseSlip方法的第二个版本：接受百分比折扣值。,5.9 重载方法,第一个leaseSlip方法具有一个空的参数表；第二个leaseSlip方法具有折扣的形参变量； public double leaseSlip(double aDiscountPercent) double fee = this.leaseSlip(); double discountedFee = fee * (100 - aDiscountPercent)/100; return discountedFee ; ,5.9 重载方法,public class TesterFive public static void main(String args) / create 2 Slip instances using different constructors Slip firstSlip = new Slip(1, 10, 20); Slip secondSlip = new Slip(2); / retrieve ,5.9 重载方法,Slip: Id = 1, Width = 10, Length = 20.0 Slip: Id = 2, Width = 12, Length = 25.0 Slip 1 fee is 800.0 with 10% discount is 720.0 Slip 2 fee is 900.0 with 20% discount is 720.0 Press any key to continue.,5.9 重载方法,Java使用异常来通知在系统运行时可能出现的错误、问题和其他异常情况 在Java中，异常也是对象,5.10 处理异常,Java 使用5个关键字来处理异常：try, catch, finally, throw, throws. 客户端使用try， catch，finally, 服务器端使用：throw，throws,5.10 处理异常,客户端每次调用可能会创建和抛出异常的方法时，都要将其调用的代码放置于try代码块中。 服务器方法会通过关键字throws包含在其头内来抛出异常 客户端会在catch代码块中捕获异常并处理 final代码块可选，一旦包含在内，不管是否捕获异常都会执行,5.10 处理异常,1.slipId的数据验证,设Bradshaw码头所连接的船台永远都不会多于50个。 需要在setSlipId setter method中验证传递给它的Id值是否在150范围内. 如果某方法准备创建和抛出异常，其头必须包含关键字throws.,5.10 处理异常,扩展后的setSlipId为： public void setSlipId(int anId) throws Exception 在此方法中检查接收到的参数值是否在合理的范围内，如果超出了范围，则对Exception进行实例化，并将其抛出。 注意不要在if语句中编写数字50，可以向Slip类中添加常量MAXIMUM_NUMBER_OF_SLIPS.,5.10 处理异常,public void setSlipId(int anId) throws Exception / reject slip Id if maximum if (anId MAXIMUM_NUMBER_OF_SLIPS) Exception e = new Exception(Slip ID not between 1 ,5.10 处理异常,2. width的数据验证,setWidth方法中的width参数值为：10,12,14,16。 首先向Slip类中添加数组来存储有效的宽度值： private static final int VALID_SLIP_WIDTHS = 10,12,14,16; 下面向setWidth头中添加throws Exception. public void setWidth(int aWidth) throws Exception;,5.10 处理异常,public void setWidth(int aWidth) throws Exception boolean validWidth = false; for (int i = 0; i VALID_SLIP_WIDTHS.length ,5.10 处理异常,带有数据验证的Slip类定义： 在此示例中，构造函数方法实际调用的是setter方法。 由于setter方法可能会抛出异常，因此构造方法头必须包括 throws Exception.,5.10 处理异常,public class Slip / attributes private int slipId; private int width; private double slipLength; / static attribute variable private static int numberOfSlips = 0; / static constants for default attribute values private static final int DEFAULT_WIDTH = 12; private static final int DEFAULT_SLIP_LENGTH = 25; / static constants for data validation private static final int MAXIMUM_NUMBER_OF_SLIPS = 50; private static final int VALID_SLIP_WIDTHS = 10,12,14,16;,5.10 处理异常,/ constructor with 3 parameters public Slip(int anId, int aWidth, double aSlipLength) throws Exception / invoke setters to populate attributes setSlipId(anId); setWidth(aWidth); setSlipLength(aSlipLength); numberOfSlips+; / constructor with 1 parameter public Slip(int anId) throws Exception / invoke 3-parameter constructor with default width ,5.10 处理异常,public double leaseSlip() double fee; switch(width) case 10: fee = 800; break; case 12: fee = 900; break; case 14: fee = 1100; break; case 16: fee = 1500; break; default: fee = 0; return fee; / override leaseSlip public double leaseSlip(double aDiscountPercent) double fee = this.leaseSlip(); double discountedFee = fee * (100 - aDiscountPercent)/100; return discountedFee ; ,5.10 处理异常,/ setter methods public void setSlipId(int anId) throws Exception / reject slip Id if maximum if (anId MAXIMUM_NUMBER_OF_SLIPS) Exception e = new Exception(Slip ID not between 1 ,5.10 处理异常,public void setWidth(int aWidth)throws Exception boolean validWidth = false; for(int i = 0; i VALID_SLIP_WIDTHS.length ,5.10 处理异常,public void setSlipLength(double aSlipLength) slipLength = aSlipLength; / getter methods public int getSlipId() return slipId; public int getWidth() return width; public double getSlipLength() return slipLength; / static method public static int getNumberOfSlips() return numberOfSlips;,5.10 处理异常,/ toString public String toString() String info; info = Slip: Id = + getSlipId() + , Width = + getWidth() + , Length = + getSlipLength(); return info; ,5.10 处理异常,public class TesterSix public static void main(String args) Slip firstSlip = null; try / force exception with invalid slip Id firstSlip = new Slip(150, 10, 25);System.out.println(firstSlip.tellAboutSelf(); catch (Exception n) / display exception message System.out.println(n); try / force exception with invalid width firstSlip = new Slip(1, 15, 25); System.out.println(firstSlip.tellAboutSelf(); ,5.10 处理异常,catch (Exception n) / display exception message System.out.println(n); finally System.out.println(finally block is always executed); try / create a slip using valid id ,5.10 处理异常,java.lang.Exception: Slip ID not between 1 & 50 java.lang.Exception: Invalid Slip Width finally block is always executed Slip: Id = 2, Width = 10, Length = 25.0 finally block is always executed Press any key to continue.,5.10 处理异常,