简单工厂模式：由一个工厂对象决定创建出哪一种类的实例。

1.抽象类

public abstract class People {
  public abstract void doSth();
}

2.具体类

public class Man extends People{
  @Override
  public void doSth() {
    System.out.println("I'm a man,I'm coding.");
  }
}

3.具体类

public class Girl extends People{

  @Override
  public void doSth() {
    System.out.println("I'm a girl,I'm eating.");
  }
}

4.工厂

public class PeopleFactory {

  public static People getSpecificPeople(String type){
    if("A-Man".equals(type)){
      return new Man();
    }else if("B-Girl".equals(type)){
      return new Girl();
    }else {
      return null;
    }
  }
}

5.测试代码

public class PeopleTestDemo {
  public static void main(String[] args) {
    People man = PeopleFactory.getSpecificPeople("A-Man");
    Objects.requireNonNull(man,"对象不存在.");
    man.doSth();

    People girl = PeopleFactory.getSpecificPeople("B-Girl");
    Objects.requireNonNull(girl,"对象不存在");
    girl.doSth();

    People foodie = PeopleFactory.getSpecificPeople("Foodie");
    Objects.requireNonNull(foodie,"对象不存在");
    foodie.doSth();
  }
}

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