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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原文地址:http://blog.51cto.com/5899363/2107838
时间: 2024-11-06 07:23:31