Motivation
ü类型码不是类型安全的，终究只是一堆数字或者一个字符串。使用类代替类型码，可以做更好的编译检查。
ü如果类型码不影响宿主类的行为，则优先考虑使用Replace Type Code with Class
Mechanics
ü为类型码建立一个类。类中应该定义一组静态变量，表示允许被创建的实例。
ü修改源类实现，将类型码替换为上面新建的类。
Eclipse重构菜单中没有直接的对应选项，一般主要应用下面两个可逆操作,完成类型码变量的替换:
[Inline]CLAIMED-->PermissionState.CLAIMED
[Extract Constant]PermissionState.CLAIMED --> CLAIMED
表示类型的Class，一般可以是enum， 静态内部类，或者一般的类。
1. 使用enum
[java]
private enum PermissionState {
REQUESTED("REQUESTEDd"),
CLAIMED("CLAIMEDd"),
DENIED("DENIED"),
GRANTED("GRANTED");
String mState;
private PermissionState(String state) {mState = state;}
private String getState() { return mState; }
<span style="white-space:pre"></span>// enum 有valueof(String arg)作为setState()
}
2. 静态内部类
[java]
static class PermissionState {
public final static PermissionState REQUESTED = new PermissionState("REQUESTED");
public final static PermissionState CLAIMED = new PermissionState("CLAIMED");
public final static PermissionState DENIED = new PermissionState("DENIED");
public final static PermissionState GRANTED = new PermissionState("GRANTED");
public final static PermissionState UNKNOWN = new PermissionState("UNKNOWN");
String mState;
// 构造函数应该private
private PermissionState(String state) {
mState = state;
}
public String getState() {
return mState;
}
}
3. 一般类，意味着有继承体系
[java]
abstract class PermissionState {
public final static String REQUESTED = "REQUESTED";
public final static String CLAIMED = "CLAIMED";
public final static String DENIED = "DENIED";
public final static String GRANTED = "GRANTED";
public final static String UNKNOWN = "UNKNOWN";
// String mState;// no field mState
public abstract String getState() ;// override by subclass
public void setState() { //switch REQUESTED, CLAIMED
}
}
一般两个特征总是必不可少，getState， setSate。 进一步，因为类型码是有限可列举的，所以setState最好是可以使用HashMap实现，static Hashmap<typecode,class>.
