我试图从一个扩展抽象类的类中调用某个方法,在抽象超类的数组上调用。有没有可能做到这一点?
users[findUser(userName)].setVehicle(vehicles[counterVehicles])
答案 0 :(得分:0)
如果你知道users[findUser(userName)]
的结果总是某种类型,你可以这样做:
((ConcreteUser)users[findUser(userName)]).setVehicle(vehicles[counterVehicles])
否则,在拨打电话之前,您必须使用instanceof
某种类型进行测试。
为避免这一切,您可以做的最好的事情是实现访问者模式。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,我在示例中只有一个访问者缩短了时间,但是您可以拥有多种类型的访问者,每个访问者都会针对不同类型的用户执行不同的操作。