你真的會用ABAP, Java和JavaScript裏的constructor麼?

若是constructor裏調用了一個成員方法，這個方法被子類override了，當初始化一個子類實例時，父類的構造函數被的調用，此時父類構造函數的上下文裏調用的成員方法，是父類的實現仍是子類的實現？ 你能不用運行代碼，就能準確說出這些語句會打印什麼出來呢？

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:

詳細分析在個人SAP community博客裏: A reminder for using constructor in OO world 要獲取更多Jerry的原創技術文章，請關注公衆號"汪子熙"或者掃描下面二維碼: