blocks|key|1457512|text|尝试以下内容：(case1)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1457513|((BaseClass)(new+InheritedClass())).DoIt()|code-block|syntax|javascript|1457514|virtual%2Boverride是在运行时解析的(所以override实际上覆盖了虚拟方法)，而new只是创建了同名的新方法，并隐藏了旧的，它是在编译时解析的，你的编译器将调用它“看到”的方法->。|1457515|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

try following: (case1)

<pre><code>((BaseClass)(new InheritedClass())).DoIt()
</code></pre>

Edit: virtual+override are resolved at runtime (so override really overrides virtual methods), while new just create new method with the same name, and hides the old, it is resolved at compile time -> your compiler will call the method it 'sees'

blocks|key|1242883|text|在第一种情况下，您在父类中隐藏了定义。这意味着只有当您将对象作为子类处理时，它才会被调用。如果将类强制转换为其父类型，则将调用父类型的方法。在第二个实例中，该方法被重写并将被调用，而不管对象是被强制转换为子类还是父类。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1242884|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

In the first case you are hiding the definition in the parent class. This means that it will only be invoked when you are dealing with the object as the child class. If you cast the class to its parent type, the parent's method will be invoked. In the second instance, the method is overridden and will be invoked regardless of whether the object is cast as the child or parent class.

blocks|key|1242911|text|这两种情况的不同之处在于，在情况1中，基本DoIt方法不会被覆盖，而只是隐藏。这意味着，取决于变量的类型取决于将调用哪个方法。例如：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1242912|BaseClass+instance1+=+new+SubClass();
instance1.DoIt();+//+Calls+base+class+DoIt+method

SubClass+instance2+=+new+SubClass();
instance2.DoIt();+//+Calls+sub+class+DoIt+method|code-block|syntax|javascript|1242913|这可能真的会令人困惑，并导致非预期的行为，如果可能的话，应该避免。因此，首选的方法是第二种情况。|1242914|entityMap^0|L|4|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

The difference between the two cases is that in case 1, the base <code>DoIt</code> method does not get overridden, just hidden. What this means is that depending on the type of the variable depends on which method will get called. For example:

<pre><code>BaseClass instance1 = new SubClass();
instance1.DoIt(); // Calls base class DoIt method

SubClass instance2 = new SubClass();
instance2.DoIt(); // Calls sub class DoIt method
</code></pre>

This can be really confusing and results in non expected behaviour and should be avoided if possible. So the preferred way would be case 2.

blocks|key|1242954|text|在情况1中，如果您使用调用继承类的DoIt()方法，而该类型被声明为基类，您甚至会看到基类的操作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1242955|/*+Results
Class1
Base1
Class2
Class2
*/
public+abstract+class+Base1
{
++++public+void+DoIt()+{+Console.WriteLine("Base1");+}
}
public++class+Class1+:+Base1+
{
++++public+new+void+DoIt()+{+Console.WriteLine("Class1");+}
}
public+abstract+class+Base2
{
++++public+virtual+void+DoIt()+{+Console.WriteLine("Base2");+}
}
public+class+Class2+:+Base2
{
++++public+override+void+DoIt()+{+Console.WriteLine("Class2");+}
}
static+void+Main(string[]+args)
{
++++var+c1+=+new+Class1();
++++c1.DoIt();
++++((Base1)c1).DoIt();

++++var+c2+=+new+Class2();
++++c2.DoIt();
++++((Base2)c2).DoIt();
++++Console.Read();
}|code-block|syntax|javascript|1242956|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

In case 1 if you used call the DoIt() method of the inherited class while the type is declared as the base class you will see the action of the base class even.

<pre><code>/* Results
Class1
Base1
Class2
Class2
*/
public abstract class Base1
{
 public void DoIt() { Console.WriteLine("Base1"); }
}
public class Class1 : Base1 
{
 public new void DoIt() { Console.WriteLine("Class1"); }
}
public abstract class Base2
{
 public virtual void DoIt() { Console.WriteLine("Base2"); }
}
public class Class2 : Base2
{
 public override void DoIt() { Console.WriteLine("Class2"); }
}
static void Main(string[] args)
{
 var c1 = new Class1();
 c1.DoIt();
 ((Base1)c1).DoIt();

 var c2 = new Class2();
 c2.DoIt();
 ((Base2)c2).DoIt();
 Console.Read();
}
</code></pre>

blocks|key|1457667|text|如果在派生类中使用了关键字override，则它会覆盖父方法。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1457668|如果在派生类中使用关键字new，则父方法隐藏了派生方法。|1457669|entityMap^0|D|8|0|C|3|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|P|8|@]|D|@]|E|$]]]|I|$]]

If keyword <code>override</code> is used in derive class then its override the parent method.

If Keyword <code>new</code> is used in derive class then derive method hided by parent method.

blocks|key|1457715|text|在这些测试中将不会显示功能差异：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1457716|BaseClass+bc+=+new+BaseClass();

bc.DoIt();

DerivedClass+dc+=+new+DerivedClass();

dc.ShowIt();|code-block|syntax|javascript|1457717|在这个示例中，被调用的Doit就是您期望被调用的Doit。|1457718|为了看到不同之处，你必须这样做：|1457719|BaseClass+obj+=+new+DerivedClass();

obj.DoIt();|1457720|如果您运行该测试，您将看到在案例1(如您所定义的)中，BaseClass中的DoIt()被调用，在案例2(如您所定义的)中，DerivedClass中的DoIt()被调用。|offset|length|style|CODE|1457721|entityMap^0|0|0|0|0|0|R|9|12|6|1Q|C|24|6|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|X|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|Z|8|@$O|10|P|11|Q|R]|$O|12|P|13|Q|R]|$O|14|P|15|Q|R]|$O|16|P|17|Q|R]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|T|$]]

The functional difference will not be show in these tests:

<pre><code>BaseClass bc = new BaseClass();

bc.DoIt();

DerivedClass dc = new DerivedClass();

dc.ShowIt();
</code></pre>

In this exmample, the Doit that is called is the one you expect to be called.

In order to see the difference you have to do this:

<pre><code>BaseClass obj = new DerivedClass();

obj.DoIt();
</code></pre>

You will see if you run that test that in the case 1 (as you defined it), the <code>DoIt()</code> in <code>BaseClass</code> is called, in case 2 (as you defined it), the <code>DoIt()</code> in <code>DerivedClass</code> is called.

blocks|key|1457762|text|在第一种情况下，它将调用派生类DoIt()方法，因为新关键字隐藏了基类DoIt()方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1457763|在第二种情况下，它将调用重写的DoIt()|1457764|++public+class+A
{
++++public+virtual+void+DoIt()
++++{
++++++++Console.WriteLine("A::DoIt()");
++++}
}

public+class+B+:+A
{
++++new+public+void+DoIt()
++++{
++++++++Console.WriteLine("B::DoIt()");
++++}
}

public+class+C+:+A
{
++++public+override+void+DoIt()
++++{
++++++++Console.WriteLine("C::DoIt()");
++++}
}|code-block|syntax|javascript|1457765|让我们创建这些类的实例|1457766|+++A+instanceA+=+new+A();

++++B+instanceB+=+new+B();
++++C+instanceC+=+new+C();

++++instanceA.DoIt();+//A::DoIt()
++++instanceB.DoIt();+//B::DoIt()
++++instanceC.DoIt();+//B::DoIt()|1457767|一切都在上面。让我们将instanceB和instanceC设置为instanceA并调用DoIt()方法并检查结果。|1457768|++++instanceA+=+instanceB;
++++instanceA.DoIt();+//A::DoIt()+calls+DoIt+method+in+class+A

++++instanceA+=+instanceC;
++++instanceA.DoIt();//C::DoIt()+calls+DoIt+method+in+class+C+because+it+was+overriden+in+class+C|1457769|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

At the first case it will call derived class DoIt() method because new keyword hides base class DoIt() method.

At the second case it will call overriden DoIt() 

<pre><code> public class A
{
 public virtual void DoIt()
 {
 Console.WriteLine("A::DoIt()");
 }
}

public class B : A
{
 new public void DoIt()
 {
 Console.WriteLine("B::DoIt()");
 }
}

public class C : A
{
 public override void DoIt()
 {
 Console.WriteLine("C::DoIt()");
 }
}
</code></pre>

let create instance of these classes

<pre><code> A instanceA = new A();

 B instanceB = new B();
 C instanceC = new C();

 instanceA.DoIt(); //A::DoIt()
 instanceB.DoIt(); //B::DoIt()
 instanceC.DoIt(); //B::DoIt()
</code></pre>

Everything is expected at above. Let set instanceB and instanceC to instanceA and call DoIt() method and check result.

<pre><code> instanceA = instanceB;
 instanceA.DoIt(); //A::DoIt() calls DoIt method in class A

 instanceA = instanceC;
 instanceA.DoIt();//C::DoIt() calls DoIt method in class C because it was overriden in class C
</code></pre>

blocks|key|1243138|text|​|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1243139|📷|atomic|offset|length|1243140|1243141|none、virtual、override、new和abstract的所有组合：|1243142|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/bb7e4087ff9d6f6c270c9343bbae06d3.png|imageAlt^0|0|0|1|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@$E|U|F|V|1|W]]|A|$]]|$1|G|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|Y|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|Q|R|-4]]]]

<a href="https://i.stack.imgur.com/NQJ9w.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/NQJ9w.png" alt="enter image description here"></a>

All combinations of none, virtual, override, new and abstract:

Wondering what the difference is between the following:

Case 1: Base Class

<pre><code>public void DoIt();
</code></pre>

Case 1: Inherited class 

<pre><code>public new void DoIt();
</code></pre>

Case 2: Base Class

<pre><code>public virtual void DoIt();
</code></pre>

Case 2: Inherited class 

<pre><code>public override void DoIt();
</code></pre>

Both case 1 and 2 appear to have the same effect based on the tests I have run. Is there a difference, or a preferred way?

Difference between new and override

编译器

想知道以下内容之间的区别是什么：案例1:基类public void DoIt();案例1:继承的类public new void DoIt();案例2:基类public virtual void DoIt();案例2:继承的类public override void DoIt();根据我运行的测试，情况1和2似乎具有相...

问new和override之间的区别
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问new和override之间的区别EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问new和override之间的区别
EN