[英]Calling methods from extended classes on array from abstract class
我试图在扩展抽象类的类的某个类中调用某个方法,该类来自抽象超类的数组。 有这样做的可能性吗?
users[findUser(userName)].setVehicle(vehicles[counterVehicles])
如果您知道users[findUser(userName)]
的结果始终为特定类型,则可以执行以下操作:
((ConcreteUser)users[findUser(userName)]).setVehicle(vehicles[counterVehicles])
否则,您必须在调用之前使用特定类型的instanceof
进行测试。
为了避免所有这些,您最好的办法就是实现访客模式。 这是怎么回事:
interface UserVisitor {
public void visit(ConcreteUser1 user1);
public void visit(ConcreteUser2 user2);
}
static class VehicleVisitor implements UserVisitor {
private Vehicle vehicle;
private Bus bus;
VehicleVisitor(Vehicle vehicle, Bus bus) {
this.vehicle = vehicle;
this.bus = bus;
}
public void visit(ConcreteUser1 user1) {
user1.setVehicle(vehicle);
}
public void visit(ConcreteUser2 user2) {
user2.setBus(bus);
}
}
static abstract class AbstractUser {
public abstract void accept(VehicleVisitor visitor);
}
static class ConcreteUser1 extends AbstractUser {
private Vehicle vehicle;
public void accept(VehicleVisitor visitor) {
visitor.visit(this);
}
public void setVehicle(Vehicle vehicle) {
this.vehicle = vehicle;
}
public Vehicle getVehicle() {
return vehicle;
}
}
static class ConcreteUser2 extends AbstractUser {
private Bus bus;
public void accept(VehicleVisitor visitor) {
visitor.visit(this);
}
public void setBus(Bus bus) {
this.bus = bus;
}
public Bus getBus() {
return bus;
}
}
static class Vehicle {
@Override
public String toString() {
return "CAR";
}
}
static class Bus {
@Override
public String toString() {
return "BUS";
}
}
public static void main(String[] args) {
List<AbstractUser> users = new ArrayList<AbstractUser>();
ConcreteUser1 user1 = new ConcreteUser1();
users.add(user1);
ConcreteUser2 user2 = new ConcreteUser2();
users.add(user2);
for (AbstractUser user : users) {
VehicleVisitor visitor = new VehicleVisitor(new Vehicle(), new Bus());
user.accept(visitor);
}
System.out.println(user1.getVehicle());
System.out.println(user2.getBus());
}
现在,在示例中,只有一个访客可以缩短访客的数量,但是您可以有多种访客类型,每个访客对不同类型的用户执行不同的操作。
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