Dart的方法覆盖

当子类尝试覆盖父类的方法时， dart会发生方法覆盖。当子类扩展父类时，它可以完全访问父类的方法，从而覆盖父类的方法。它是通过重新定义父类中存在的相同方法来实现的。

当您必须为不同的子类执行不同的功能时，此方法很有用，因此我们可以通过覆盖它来简单地重新定义内容。

要点：

1. 一个方法只能在子类中被覆盖，而不能在父类本身中被覆盖。
2. 子类和父类中定义的方法都应该是精确的副本，从名称到参数列表，除了方法内部存在的内容，即它可以和不能相同。
3. 在父类中声明为 final 或 static 的方法不能被子类覆盖。
4. 父类的构造函数不能被继承，所以它们不能被子类覆盖。

示例 1：方法覆盖的简单案例。

Dart

// Dart Program to illustrate the 
// method overriding concept
class SuperGeek {
    
  // Creating a method
  void show(){
    print("This is class SuperGeek.");
  }
}
   
class SubGeek extends SuperGeek {
    
  // Overriding show method
  void show(){
    print("This is class SubGeek child of SuperGeek.");
  }
}
   
void main() {
  // Creating objects
  //of both the classes
  SuperGeek geek1 = new SuperGeek();
  SubGeek geek2 = new SubGeek();
    
  // Calling same function
  // from both the classes
  // object to show method overriding
  geek1.show();
  geek2.show();
}

输出：

This is class SuperGeek.
This is class SubGeek child of SuperGeek.

示例 2：当有多个子类时。

Dart

// Dart Program to illustrate the 
// method overriding concept
  
class SuperGeek {
    
  // Creating a method
  void show(){
    print("This is class SuperGeek.");
  }
}
   
class SubGeek1 extends SuperGeek {
    
  // Overriding show method
  void show(){
    print("This is class SubGeek1 child of SuperGeek.");
  }
}
   
class SubGeek2 extends SuperGeek {
  // Overriding show method
   
  void show(){
    print("This is class SubGeek2 child of SuperGeek.");
  }
}
  
void main() {
    
  // Creating objects of both the classes
  SuperGeek geek1 = new SuperGeek();
  SubGeek1 geek2 = new SubGeek1();
  SubGeek2 geek3 = new SubGeek2();
    
  // Calling same function
  // from both the classes
  // object to show method 
  // overriding
  geek1.show();
  geek2.show();
  geek3.show();
}

输出：

This is class SuperGeek.
This is class SubGeek1 child of SuperGeek.
This is class SubGeek2 child of SuperGeek.