重构之switch惊悚现身
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未重构之前的代码
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public class Employee
{
private int _type;
static final int ENGINEER = 0;
static final int SALESMAN = 1;
static final int MANAGER = 2
Employee(int type)
{
_type = type;
}
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int payAmout()
{
switch (_type){
? case ENGINEER:
? return 1;
? case SALESMAN:
? return 2;
? case MANAGER:
? return 3;
? default:
? throw new RuntimeException("error");
}
}
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?
}
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第一步，我们进行自封装字段，代码变为：
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public class Employee
{
private int _type;
static final int ENGINEER = 0;
static final int SALESMAN = 1;
static final int MANAGER = 2;
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Employee(int type)
{
setType(type);
}
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int payAmout()
{
switch (getType()){
? case ENGINEER:
? return 1;
? case SALESMAN:
? return 2;
? case MANAGER:
? return 3;
? default:
? throw new RuntimeException("error");
}
}
void setType(int type)
{
_type = type;
}
int getType()
{
return _type;
}
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}
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第二步，我们增加间接层
public abstract class EmployeeType {
abstract int getTypeCode();
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}
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第三部，创建间接层子类
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public class Engineer extends EmployeeType {
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int getTypeCode(){
return Employee.ENGINEER;
}
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}
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public class Manager extends EmployeeType {
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int getTypeCode() {
return Employee.MANAGER;
}
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}
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public class SalesMan extends EmployeeType
{
? ? ? ?int getTypeCode()
? ? ? ?{
? ? ? ? ? return Employee.SALESMAN;
? ? ? ?}
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}
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第四步，用声明的间接层去替换Employee中的类型码成员变量
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public class Employee
{
EmployeeType _type;
static final int ENGINEER = 0;
static final int SALESMAN = 1;
static final int MANAGER = 2;
?
Employee(int arg)
{
setType(arg);
}
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int payAmout(int arg)
{
switch (arg){
? case ENGINEER:
? return 1;
? case SALESMAN:
? return 2;
? case MANAGER:
? return 3;
? default:
? throw new RuntimeException("error");
}
}
void setType(int arg)
{
switch(arg){
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case ENGINEER:
_type = new Engineer();
break;
case MANAGER:
_type = new Manager();
break;
case SALESMAN:
_type = new SalesMan();
break;
default:
throw new RuntimeException("code error");
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}
}
int getType()
{
return _type.getTypeCode();
}
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}
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第五步，建立一个工厂函数，来生产EmployeeType实例
public abstract class EmployeeType {
abstract int getTypeCode();
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static final int ENGINEER = 0;
static final int SALESMAN = 1;
static final int MANAGER = 2;
static EmployeeType newType(int code)
{
switch(code){
case ENGINEER:
? ?return new Engineer();
case SALESMAN:
return new SalesMan();
case MANAGER:
return new Manager();
default:
throw new RuntimeException("wrongcode");
}
}
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}
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第六步，去掉Employee当中的类型码
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public class Employee
{
EmployeeType _type;
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Employee(int arg)
{
setType(arg);
}
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int payAmout()
{
switch (getType()){
? case EmployeeType.ENGINEER:
? return 1;
? case EmployeeType.MANAGER:
? return 2;
? case EmployeeType.SALESMAN:
? return 3;
? default:
? throw new RuntimeException("error");
}
}
void setType(int arg)
{
_type = EmployeeType.newType(arg);
}
int getType()
{
return _type.getTypeCode();
}
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}
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第七步，将payAmout函数提到它应该在的地方
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public abstract class EmployeeType {
abstract int getTypeCode();
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static final int ENGINEER = 0;
static final int SALESMAN = 1;
static final int MANAGER = 2;
static EmployeeType newType(int code)
{
switch(code){
case ENGINEER:
? ?return new Engineer();
case SALESMAN:
return new SalesMan();
case MANAGER:
return new Manager();
default:
throw new RuntimeException("wrongcode");
}
}
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int payAmout()
{
switch (getTypeCode()){
? case ENGINEER:
? return 1;
? case MANAGER:
? return 2;
? case SALESMAN:
? return 3;
? default:
? throw new RuntimeException("error");
}
}
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}
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第八步，将payAccout声明为abstract,然后各子类分别实现这个方法
public class Engineer extends EmployeeType {
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int getTypeCode(){
return ENGINEER;
}
int payAccount(){
return 2;
}
}
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public class Manager extends EmployeeType {
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int getTypeCode() {
return MANAGER;
}
int payAccount()
{
return 3;
}
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}
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public class SalesMan extends EmployeeType {
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int getTypeCode() {
return SALESMAN;
}
int payAccount()
{
return 1;
}
}
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第九步，修改Employee的payAccount函数
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public class Employee
{
EmployeeType _type;
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Employee(int arg)
{
setType(arg);
}
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int payAmout()
{
return _type.payAccount();
}
void setType(int arg)
{
_type = EmployeeType.newType(arg);
}
int getType()
{
return _type.getTypeCode();
}
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}
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