如果constructor裡呼叫了一個成員方法，這個方法被子類override了，當初始化一個子類例項時，父類的建構函式被的呼叫，此時父類建構函式的上下文裡呼叫的成員方法，是父類的實現還是子類的實現？
你能不用執行程式碼，就能準確說出這些語句會列印什麼出來呢？

ABAP

class ZCL_SUPER definition public
  create public .
public section.
  methods CONSTRUCTOR .
  methods SET_I
    importing
      !IV_I type INT4 .
protected section.
private section.
  data MV_SUPER type INT4 .
ENDCLASS.
CLASS ZCL_SUPER IMPLEMENTATION.
  method CONSTRUCTOR.
    me->set_i( 100 ).
  endmethod.
  method SET_I.
    me->mv_super = iv_i.
  endmethod.
ENDCLASS. class ZCL_SUB definition public
  inheriting from ZCL_SUPER
  final
  create public .
public section.
  methods PRINT .
  methods SET_I
    redefinition .
protected section.
private section.
  data MV_SUB type I value 1 ##NO_TEXT. ENDCLASS.
CLASS ZCL_SUB IMPLEMENTATION.
  method PRINT. WRITE: / ' sub:' , mv_sub.
  endmethod.
  METHOD set_i. super->set_i( iv_i = iv_i ).
    me->mv_sub = iv_i. WRITE: / 'mv_sub assigned by: ' , iv_i.
  ENDMETHOD.
ENDCLASS. 

測試：

NEW zcl_sub( )->print( ). 

測試結果：sub: 1

Java

public class SuperClass { private int mSuperX; public SuperClass() {
        setX(99);
    } public void setX(int x) {
        mSuperX = x;
    }
} public class SubClass extends SuperClass { private int mSubX = 1; public SubClass() {} @Override public void setX(int x) { super.setX(x);
        mSubX = x;
        System.out.println("SubX is assigned " + x);
    } public void printX() {
        System.out.println("SubX = " + mSubX);
    }
} 

test:

public static void main(String[] args) {
        SubClass sc = new SubClass();
        sc.printX();
    } 

測試結果：

JavaScript

function SuperClass(){ this.setX(99);
}

SuperClass.prototype = { mSuperX : 0, setX : function(x){ this.mSuperX = x;
    }
}; function SubClass(){  
    SuperClass.call(this); this.mSubX = 1;
}  

SubClass.prototype = new SuperClass();  

SubClass.prototype.setX = function(x){
        SuperClass.prototype.setX(x); this.mSubX = x; console.log("SubX is assigned " + x);
};

SubClass.prototype.print = function(){ console.log("SubX: " + this.mSubX);
} 

test:

var sub = new SubClass();
sub.print(); 

測試結果:

詳細分析在我的SAP community部落格裡: A reminder for using constructor in OO world
要獲取更多Jerry的原創技術文章，請關注公眾號"汪子熙"或者掃描下面二維碼:

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/24475491/viewspace-2152625/，如需轉載，請註明出處，否則將追究法律責任。