在Java中基于off对象类型的列表中显示元素

Question

public interface Vehicle {
   void vehicleName();
}

public class Car implements Vehicle{

    @Override
    public String vehicleName() {
        System.out.println("I'm a car");
    }
    
}

public class Bike implements Vehicle{

    @Override
    public String vehicleName() {
        System.out.println("I'm a bike");
    }
    
}


public class Transportation {

List<Vehicle> vehicleList = new ArrayList<>();

}

Answer 1

您可以构建一个映射，其中键是vehicle实例的class，value是count（特定类型在列表中出现的次数）。

 Map<Class<? extends Vehicle>, Long> result = vehicleList.stream()
            .collect(Collectors.groupingBy(Vehicle::getClass, Collectors.counting()));

假设您有两辆车和一辆自行车,那么打印result映射将打印规范类名,

{class <your_java_package_path>.Bike=1, class <your_java_package_path>.Car=2}

若要获取简单类名，请调用getSimplename作为：

result.forEach((clazz, count) -> System.out.println(clazz.getSimpleName() + " " + count));

Bike 1
Car 2