第一個例子
第一個類:
影片類:
簡單的純數據類:
package one;
public class Movie {
public static final int REGULAR=0;
public static final int NEW_RELEASE=1;
public static final int CHILDRENS=2;
private String _title;
private int _priceCode;
public Movie(String title,int priceCode){
_title=title;
_priceCode=priceCode;
}
public int getPriceCode() {
return _priceCode;
}
public void setpriceCode(int arg) {
_priceCode = arg;
}
public String getTitle(){
return _title;
}
}
Rental(租賃)
Rental表示某顧客租了一部影片:
package one;
//租賃
class Rental {
private Movie _movie;
private int _daysRented;
public Rental(Movie movie, int daysRented) {
_movie = movie;
_daysRented = daysRented;
}
public int getDaysRented() {
return _daysRented;
}
public Movie getMovie() {
return _movie;
}
Customer(顧客)
Customer表示顧客,它也像其它類一樣,它也擁有數據和相應的訪問函數:
package one;
import java.util.Enumeration;
import java.util.Vector;
public class Customer {
private String _name;
private Vector _rentals=new Vector();
public Customer(String name){
_name=name;
}
public void addRental(Rental arg){
_rentals.addElement(arg);
}
public String getName(){
return _name;
}
//Customer還提供了一個用於生成詳單的函數:
public String statement(){
double totalAmount=0;
int frequentRenterPoints=0;
Enumeration rentals=_rentals.elements();
String result="Rental Record for "+getName()+"\n";
while(rentals.hasMoreElements()){
double thisAmount=0;
Rental each=(Rental) rentals.nextElement();
//determine qmounts for each line
switch(each.getMovie().getPriceCode()){
case Movie.REGULAR:
thisAmount+=2;
if(each.getDaysRented()>2)
thisAmount +=(each.getDaysRented()-2)*1.5;
break;
case Movie.NEW_RELEASE:
thisAmount+=each.getDaysRented()*3;
break;
case Movie.CHILDRENS:
thisAmount +=1.5;
if(each.getDaysRented()>3)
thisAmount+=(each.getDaysRented()-3)*1.5;
break;
}
//add frequent renter points
frequentRenterPoints ++;
//add bonus for a two day new release rental
if((each.getMovie().getPriceCode()==Movie.NEW_RELEASE)&&each.getDaysRented()>1)
frequentRenterPoints ++;
//show figures for this rental
result +="\t" +each.getMovie().getTitle()+"\t"+String.valueOf(thisAmount)+"\n";
totalAmount+=thisAmount;
}
//add footer lines
result+="Amount owed is"+String.valueOf(totalAmount)+"\n";
result +="You earned"+String.valueOf(frequentRenterPoints)+"frequent renter points";
return result;
}
}
第一次重構:
分解並重組:
1,代碼塊越小,代碼的功能就越容易管理,代碼的處理和移動也就越輕鬆。
:提煉amountFor()函數並修改不喜歡的變量名:
package one;
import java.util.Enumeration;
import java.util.Vector;
public class Customer2 {
private String _name;
private Vector _rentals=new Vector();
public Customer2(String name){
_name=name;
}
public void addRental(Rental arg){
_rentals.addElement(arg);
}
public String getName(){
return _name;
}
public String statement(){
double totalAmount=0;
int frequentRenterPoints=0;
Enumeration rentals=_rentals.elements();
String result="Rental Record for "+getName()+"\n";
while(rentals.hasMoreElements()){
double thisAmount=0;
Rental each=(Rental) rentals.nextElement();
thisAmount=amountFor(each);
//System.out.println(thisAmount);
//add frequent renter points
frequentRenterPoints ++;
//add bonus for a two day new release rental
if((each.getMovie().getPriceCode()==Movie.NEW_RELEASE)&&each.getDaysRented()>1)
frequentRenterPoints ++;
//show figures for this rental
result +="\t" +each.getMovie().getTitle()+"\t"+String.valueOf(thisAmount)+"\n";
totalAmount+=thisAmount;
}
//add footer lines
result+="Amount owed is"+String.valueOf(totalAmount)+"\n";
result +="You earned"+String.valueOf(frequentRenterPoints)+"frequent renter points";
return result;
}
private double amountFor(Rental aRental) {
double result=0;
//determine qmounts for each line
switch(aRental.getMovie().getPriceCode()){
case Movie.REGULAR:
result+=2;
if(aRental.getDaysRented()>2)
result +=(getDaysRented()-2)*1.5;
break;
case Movie.NEW_RELEASE:
result+=aRental.getDaysRented()*3;
break;
case Movie.CHILDRENS:
result +=1.5;
if(aRental.getDaysRented()>3)
result+=(aRental.getDaysRented()-3)*1.5;
break;
}
return result;
}
}
//這裏作者忽略了thisAmount的返回類型,返回的是int,而不是double。應返回double。
//這裏,作者順便改變了amount裏一些不喜歡的變量名
2,重要:函數應該放在它所使用的數據的所屬對象內
:amountFor()應該移動到Rental類去
Rental類中:
double getCharge() {
double result=0;
//determine qmounts for each line
switch(getMovie().getPriceCode()){
case Movie.REGULAR:
result+=2;
if(getDaysRented()>2)
result +=(getDaysRented()-2)*1.5;
break;
case Movie.NEW_RELEASE:
result+=getDaysRented()*3;
break;
case Movie.CHILDRENS:
result +=1.5;
if(getDaysRented()>3)
result+=(getDaysRented()-3)*1.5;
break;
}
return result;
}
statement函數如下:
public String statement(){
double totalAmount=0;
int frequentRenterPoints=0;
Enumeration rentals=_rentals.elements();
String result="Rental Record for "+getName()+"\n";
while(rentals.hasMoreElements()){
double thisAmount=0;
Rental each=(Rental) rentals.nextElement();
thisAmount=each.getCharge();
//System.out.println(thisAmount);
//add frequent renter points
frequentRenterPoints ++;
//add bonus for a two day new release rental
if((each.getMovie().getPriceCode()==Movie.NEW_RELEASE)&&each.getDaysRented()>1)
frequentRenterPoints ++;
//show figures for this rental
result +="\t" +each.getMovie().getTitle()+"\t"+String.valueOf(thisAmount)+"\n";
totalAmount+=thisAmount;
}
//add footer lines
result+="Amount owed is"+String.valueOf(totalAmount)+"\n";
result +="You earned"+String.valueOf(frequentRenterPoints)+"frequent renter points";
return result;
}
3,去除不必要的臨時變量:
:去掉 thisAmount,用each.getCharge()代替。
:臨時變量容易引發問題,它們會導致大量參數傳來傳去,而其實完全沒有必要。在函數中,尤其是長長的函數中,還容易跟丟。
:當然這麼做也會付出性能上的代價。此例中,getCharge()會被修改兩遍。
:但是如果代碼有良好的組織和管理,優化就會有很好的效果。
:這也是有時會困擾我的一個問題。既然可以這麼處理,那挺好的。
public String statement(){
double totalAmount=0;
int frequentRenterPoints=0;
Enumeration rentals=_rentals.elements();
String result="Rental Record for "+getName()+"\n";
while(rentals.hasMoreElements()){
Rental each=(Rental) rentals.nextElement();
//add frequent renter points
frequentRenterPoints ++;
//add bonus for a two day new release rental
if((each.getMovie().getPriceCode()==Movie.NEW_RELEASE)&&each.getDaysRented()>1)
frequentRenterPoints ++;
//show figures for this rental
result +="\t" +each.getMovie().getTitle()+"\t"+String.valueOf(each.getCharge())+"\n";
totalAmount+=each.getCharge();
}
//add footer lines
result+="Amount owed is"+String.valueOf(totalAmount)+"\n";
result +="You earned"+String.valueOf(frequentRenterPoints)+"frequent renter points";
return result;
}
4,提煉each.getFrequentRenterPoints()函數
:同2,此函數主要用到Rental裏面的數據。提煉函數,可以讓代碼更簡潔,耐看。
public String statement(){
double totalAmount=0;
int frequentRenterPoints=0;
Enumeration rentals=_rentals.elements();
String result="Rental Record for "+getName()+"\n";
while(rentals.hasMoreElements()){
Rental each=(Rental) rentals.nextElement();
frequentRenterPoints=each.getFrequentRenterPoints();
//show figures for this rental
result +="\t" +each.getMovie().getTitle()+"\t"+String.valueOf(each.getCharge())+"\n";
totalAmount+=each.getCharge();
}
//add footer lines
result+="Amount owed is"+String.valueOf(totalAmount)+"\n";
result +="You earned"+String.valueOf(frequentRenterPoints)+"frequent renter points";
return result;
}
class Rental...
public int getFrequentRenterPoints() {
if((getMovie().getPriceCode()==Movie.NEW_RELEASE)&&getDaysRented()>1){
return 2;
}else{
return 1;
}
}
5.去除臨時變量:
:用Customer類的getTotalCharge()取代totalAmount()
:不得不復制循環。
class Customer...
public String statement(){
int frequentRenterPoints=0;
Enumeration rentals=_rentals.elements();
String result="Rental Record for "+getName()+"\n";
while(rentals.hasMoreElements()){
Rental each=(Rental) rentals.nextElement();
frequentRenterPoints=each.getFrequentRenterPoints();
//show figures for this rental
result +="\t" +each.getMovie().getTitle()+"\t"+String.valueOf(each.getCharge())+"\n";
}
//add footer lines
result+="Amount owed is"+String.valueOf(getTotalCharge())+"\n";
result +="You earned"+String.valueOf(frequentRenterPoints)+"frequent renter points";
return result;
}
private double getTotalCharge() {
double result=0;
Enumeration rentals=_rentals.elements();
while(rentals.hasMoreElements()){
Rental each=(Rental) rentals.nextElement();
result+=each.getCharge();
}
return result;
}
:相似的,用Customer類的getTotalFrequentRenterPoints()取代frequentRenterPoints。
public String statement(){
Enumeration rentals=_rentals.elements();
String result="Rental Record for "+getName()+"\n";
while(rentals.hasMoreElements()){
Rental each=(Rental) rentals.nextElement();
//show figures for this rental
result +="\t" +each.getMovie().getTitle()+"\t"+String.valueOf(each.getCharge())+"\n";
}
//add footer lines
result+="Amount owed is"+String.valueOf(getTotalCharge())+"\n";
result +="You earned"+String.valueOf(getTotalFrequentRenterPoints())+"frequent renter points";
return result;
}
private int getTotalFrequentRenterPoints() {
int result=0;
Enumeration rentals=_rentals.elements();
while(rentals.hasMoreElements()){
Rental each=(Rental) rentals.nextElement();
result+=each.getFrequentRenterPoints();
}
return result;
}
6.把getCharge()放到Movie裏去。
:此函數中用到的更多是Movie的屬性
:把租借時間當參數傳入。
class Movie..
double getCharge(int daysRented){
double result=0;
//determine qmounts for each line
switch(getPriceCode()){
case Movie.REGULAR:
result+=2;
if(daysRented>2)
result +=(daysRented-2)*1.5;
break;
case Movie.NEW_RELEASE:
result+=daysRented*3;
break;
case Movie.CHILDRENS:
result +=1.5;
if(daysRented>3)
result+=(daysRented-3)*1.5;
break;
}
return result;
}
class Rental...
double getCharge(){
return _movie.getCharge(_daysRented);
}
7,對getFrequentRenterPoints()也採取相應的策略。
class Movie..
int getFrequentRenterPoints(int daysRented){
//add bonus for a two day new release rental
if((getPriceCode()==Movie.NEW_RELEASE)&&daysRented>1){
return 2;
}else{
return 1;
}
}
class Rental...
public int getFreqentRenterPoints() {
return _movie.getFrequentRenterPoints(_daysRented);
}
8.繼承
:數種影片類型,以不同的方式回答相同的問題----state模式。
:在Price對象內進行子類化動作,就可在任何必要時候修改價格。
:Replace Type Code with State/Strategy,將與類型相關的行爲搬遷至State模式內。
:任何時候都通過取值函數和設值函數來訪問類型代碼。對構造函數加以改造。
class Novie
public Movie(String title,int priceCode){
_title=title;
setPriceCode(priceCode);
}
:新建Price類,加入抽象函數,提供類型相關行爲。在子類中加上對應的具體函數。
abstract class Price {
abstract int getPriceCode();
}
public class ChildrensPrice extends Price{
int getPriceCode() {
return Movie.CHILDRENS;
}
}
public class NewReleasePrice extends Price{
int getPriceCode() {
return Movie.NEW_RELEASE;
}
}
public class RegularPrice extends Price{
int getPriceCode() {
return Movie.REGULAR;
}
}
:修改Movie類的"價格代號"訪問函數(取值函數/設值函數),讓他們使用新類。
:不再保存_price-Code變量
class Movie..{
private Price _price;
public int getPriceCode() {
return _price.getPriceCode();
}
public void setPriceCode(int arg) {
switch(arg){
case REGULAR:
_price=new RegularPrice();
break;
case CHILDRENS:
_price=new ChildrensPrice();
break;
case NEW_RELEASE:
_price=new NewReleasePrice();
break;
default:
throw new IllegalArgumentException("Incorrect Price Code");
}
}
8.2 對getCharge()實施Move Method(142)
class Movie...
double getCharge(int daysRented){
return _price.getCharge(daysRented);
}
class Price...
double getCharge(int daysRented){
double result=0;
//determine qmounts for each line
switch(getPriceCode()){
case Movie.REGULAR:
result+=2;
if(daysRented>2)
result +=(daysRented-2)*1.5;
break;
case Movie.NEW_RELEASE:
result+=daysRented*3;
break;
case Movie.CHILDRENS:
result +=1.5;
if(daysRented>3)
result+=(daysRented-3)*1.5;
break;
}
return result;
}
8.3 :Replace Conditional with Polymorphism(255)
先做如上總結。