extents 和 implements都能实现抽象类定义规范,应该怎么选择呢?

• 如果要复用抽象类里的非抽象方法则选择 extents
• 如果单纯当标准定义规范的话用implements

extents实现抽象类

/*
abstract抽象类 用于定于标准。不能实例化对象，抽象方法子类必须实现

*/
abstract class Animal {
  eat(); //抽象类
  printInfo() {
    //非抽象方法,子类不必实现
    print("Animal");
  }
}

class Dog extends Animal {
  @override
  eat() {
    print("小狗在吃骨头");
  }
}

class Cat extends Animal {
  @override
  eat() {
    print("小狗在吃骨头");
  }
}

void main() {
  //多态,父类指针指向子类对象
  Animal dog = Dog();
  dog.eat();  
}

implements实现抽象类

abstract class Animal {
  eat(); //抽象类
}

class Dog implements Animal {
  @override
  eat() {
    print("小狗在吃骨头");
  }
}

class Cat implements Animal {
  @override
  eat() {
    print("小狗在吃骨头");
  }
}

void main() {
  //多态,父类指针指向子类对象
  Animal dog = Dog();
  dog.eat();
  runApp(const MyApp());
}

一个类实现多个接口

abstract class A {
  printA();
}

abstract class B {
  printB();
}

class C implements A, B {
  @override
  printA() {}
  @override
  printB() {}
}

void main() {
  C c = C();
  c.printA;
  c.printB;
  runApp(const MyApp());
}

mixin 实现多继承

/*
mixin 不能有构造函数,必须继承自object
如果混入的两个类有相同方法名称,会执行混入后边那个
类型判断 c is A  c is B c is C 都为true
*/

mixin class A {
  String info = "this is info";
  printA() {
    print("A");
  }

  run() {
    print("RunA");
  }
}

mixin class B {
  printB() {
    print("B");
  }

  run() {
    print("RunB");
  }
}

class C with A, B {}

void main() {
  C c = C();
  c.printA();
  c.printB();
  c.run();
  print(c.info);

  //类型判断
  if (c is A) {
    print("is A");
  }
  if (c is B) {
    print("is B");
  }
  if (c is C) {
    print("is C");
  }

  runApp(const MyApp());
}