重构读书笔记-8_13-Replace_Type_Code_wi

重构第八章

13.Replace Type Code With Class(以类取代型别码)

class之中有一个数值型别码，但它不影响class的行为。以一个新的class替换该数值型别码。

Example:

class Person {
    public static final int O=0;
    public static final int A=1;
    public static final int B=2;
    public static final int C=3;
    private int _bloodGroup;
    
    public Person(int bloodGroup) {
        _bloodGroup = bloodGroup;
    }
    public void setBloodGroup(int arg) {
        _bloodGroup = arg;
    }
    public int getBloodGroup() {
        return _bloodGroup;
    }
}

End:

class Person...
    public int getBloodGroupCode() {
        return _bloodGroup.getCode();
    }
    public BloodGroup getBloodGroup() {
        return _bloodGroup;
    }
    public Person(BloodGroup bloodGroup) {
        _bloodGroup = bloodGroup;
    }
    public void setBloodGroup(BloodGroup arg) {
        _bloodGroup = arg;
    }

class BloodGroup...
    public static final BloodGroup O = new BloodGroup(0);
    public static final BloodGroup A = new BloodGroup(1);
    public static final BloodGroup B = new BloodGroup(2);
    public static final BloodGroup AB = new BloodGroup(3)
    private static final BloodGroup[] _values = {O,A,B,AB};
    private final int _code;
    private BloodGroup(int code) {
        _code = code;
    }
    public int getCode() {
        return _code;
    }
    public static BloodGroup code(int arg) {
        return _values[arg];
    }

Conclusion:

Replace Type Code With Class(以类取代型别码)的方法，Person class在构造的时候直接传入BloodGroup 对象，相当于有了参数校验的功能(即运行期校验功能)。

注意

重构必须在有单元测试的情况下，保证之前的功能修改后不收影响。切记！！！