Java Stream中查找元素并处理默认情况的最佳实践

public void findVehicleOldMethod(List<Vehicle> vehicles, String rego) {
    System.out.println("Input a vehicle rego: " + rego); // 模拟输入
    for (Vehicle vehicle : vehicles) {
        if (vehicle.getRego().equals(rego)) {
            System.out.println(vehicle.toString());
            return; // 找到即返回
        }
    }
    System.out.println("The vehicle does not exist."); // 未找到
}

public void findVehicleBasicStream(List<Vehicle> vehicles, String rego) {
    System.out.println("Input a vehicle rego: " + rego); // 模拟输入
    vehicles.stream()
            .filter(vehicle -> vehicle.getRego().equals(rego.toUpperCase()))
            .forEach(System.out::println);
    // 问题：如果未找到，这里不会打印“The vehicle does not exist.”
}

import java.util.List;
import java.util.Optional; // 确保导入Optional

// 假设Vehicle类有getRego()和toString()方法
class Vehicle {
    private String rego;
    private String model;

    public Vehicle(String rego, String model) {
        this.rego = rego;
        this.model = model;
    }

    public String getRego() {
        return rego;
    }

    @Override
    public String toString() {
        return "Vehicle [Rego=" + rego + ", Model=" + model + "]";
    }
}

public class VehicleFinder {

    public void findVehicleWithStream(List<Vehicle> vehicles, String regoToFind) {
        System.out.println("Input a vehicle rego: " + regoToFind);

        vehicles.stream()
                // 1. 过滤：根据注册号筛选匹配的车辆
                .filter(v -> v.getRego().equalsIgnoreCase(regoToFind)) // 使用equalsIgnoreCase处理大小写不敏感
                // 2. 查找第一个：获取第一个匹配的车辆，返回Optional<Vehicle>
                .findFirst()
                // 3. 条件执行：如果Optional中存在值，则执行第一个Lambda；否则执行第二个Lambda
                .ifPresentOrElse(
                    System.out::println, // 如果找到车辆，打印车辆信息
                    () -> System.out.println("The vehicle does not exist.") // 如果未找到，打印错误信息
                );
    }

    public static void main(String[] args) {
        List<Vehicle> vehicleList = List.of(
            new Vehicle("ABC123", "Sedan"),
            new Vehicle("XYZ789", "SUV"),
            new Vehicle("DEF456", "Truck")
        );

        VehicleFinder finder = new VehicleFinder();

        // 示例1：找到匹配车辆
        finder.findVehicleWithStream(vehicleList, "xyz789");
        System.out.println("---");
        // 示例2：未找到匹配车辆
        finder.findVehicleWithStream(vehicleList, "GHI000");
        System.out.println("---");
        // 示例3：大小写敏感测试 (如果使用 equalsIgnoreCase)
        finder.findVehicleWithStream(vehicleList, "abc123");
    }
}