如果constructor里调用了一个成员方法，这个方法被子类override了，当初始化一个子类实例时，父类的构造函数被的调用，此时父类构造函数的上下文里调用的成员方法，是父类的实现还是子类的实现？
你能不用运行代码，就能准确说出这些语句会打印什么出来呢？

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.

测试：

NEW zcl_sub( )->print( ).

测试结果：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(); }

测试结果：

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();

测试结果:

详细分析在我的SAP community博客里: A reminder for using constructor in OO world
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