Grails類的初始化

Question

我對groovy/grails的初始化有個疑問。當我有以下類時，sInstance不會傳入SService初始化。

class SService { 

    String sInstance 
    String app 

public getSInstance{ 
    return sInstance 
    } 
} 

此返回null，其中

class A { 

    String sInstance 
    String app 
    String dbInstance 

public initializeSService{ 
    SService s = new SService(sInstance:sInstance, app:app) 
    } 
} 

從SService類返回sInstance變量：

class A { 

    String sInstance 
    String app 
    String dbInstance 

    SService s = new SService(sInstance:sInstance, app:app) 
} 

SService類。

爲什麼會這樣以及如何讓SService對象用類A的構造函數初始化？

Answer 1

你不能做這樣的事情：

class A { 

    String sInstance 
    String app 
    String dbInstance 

    SService s = new SService(sInstance:sInstance, app:app) 
} 

與問題是，當你創建SService的一個實例，sInstance尚未初始化。如果要將sInstance傳遞給A類中的某個其他類的構造函數，則必須在sInstance被賦予一個值之後執行此操作，例如在完全構造A之後調用的方法。

編輯：

試圖澄清從下面的評論的內容：

class A { 
    String sInstance 
    String app 
    String dbInstance 

    void anyMethod() { 
     // this will work as long as you have initialized sInstance 
     SService s = new SService(sInstance:sInstance, app:app) 
    } 
} 

取決於你真正要做的，或許真的在這個方向：

class A { 
    String sInstance 
    String app 
    String dbInstance 
    SService s 

    void initializeS() { 
     if(s == null) { 
      // this will work as long as you have initialized sInstance 
      s = new SService(sInstance:sInstance, app:app) 
     } 
    } 
} 

或者：

class A { 
    String sInstance 
    String app 
    String dbInstance 
    SService theService 

    SService getTheService() { 
     if(theService == null) { 
      // this will work as long as you have initialized sInstance 
      theService = new SService(sInstance:sInstance, app:app) 
     } 
     theService 
    } 

    def someMethodWhichUsesTheService() { 
     getTheService().doSomethingToIt() 
    } 
}