Java方法返回值与类型转换的深入理解：探讨多态返回的局限性与替代方案

public class Employee {
    String name;
    int age;

    public Employee (String name, int age){
        this.name = name;
        this.age = age;
    }

    public int getAge() {
        return age;
    }

    public String getName(){
        return name;
    }
}

Employee tomJones = new Employee("Tom Jones", 38);

// 这是无效的Java代码！
public class Example {
    public String getData() { return "Hello"; }
    public int getData() { return 123; } // 编译错误：重复的方法签名
}

public class Employee {
    private String name; // 良好的实践是使用private修饰字段
    private int age;

    public Employee(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() { // 返回String类型
        return name;
    }

    public int getAge() { // 返回int类型
        return age;
    }

    // 可以添加其他方法，例如获取所有信息
    public String getDetails() {
        return "Name: " + name + ", Age: " + age;
    }
}

// 使用示例
Employee tomJones = new Employee("Tom Jones", 38);
String employeeName = tomJones.getName(); // 返回 "Tom Jones" (String)
int employeeAge = tomJones.getAge();     // 返回 38 (int)

System.out.println("Name: " + employeeName);
System.out.println("Age: " + employeeAge);

import java.util.HashMap;
import java.util.Map;

public class ConfigReader {
    private Map<String, Object> properties;

    public ConfigReader() {
        this.properties = new HashMap<>();
        this.properties.put("appName", "MyApplication");
        this.properties.put("version", 1.0);
        this.properties.put("port", 8080);
    }

    /**
     * 根据键和期望的类型获取配置值。
     *
     * @param key  配置项的键
     * @param type 期望的返回类型
     * @param <T>  泛型类型
     * @return 对应类型的值，如果类型不匹配或键不存在则返回null
     */
    public <T> T getProperty(String key, Class<T> type) {
        Object value = properties.get(key);
        if (value != null && type.isInstance(value)) {
            return type.cast(value); // 安全的类型转换
        }
        return null;
    }

    // 另一种更通用的泛型方法，需要调用者自行处理类型转换
    public <T> T getGenericValue(String key) {
        // 这里的强制转换是未经检查的，需要调用者确保类型正确，或者在内部进行更严格的检查
        @SuppressWarnings("unchecked")
        T value = (T) properties.get(key);
        return value;
    }
}

// 使用示例
ConfigReader reader = new ConfigReader();

// 使用带有Class参数的泛型方法
String appName = reader.getProperty("appName", String.class);
Double version = reader.getProperty("version", Double.class);
Integer port = reader.getProperty("port", Integer.class);

System.out.println("App Name: " + appName);
System.out.println("Version: " + version);
System.out.println("Port: " + port);

// 尝试获取不存在的键或类型不匹配的键
Boolean enabled = reader.getProperty("enabled", Boolean.class); // null
Integer wrongType = reader.getProperty("appName", Integer.class); // null

System.out.println("Enabled: " + enabled);
System.out.println("Wrong Type: " + wrongType);

// 使用不带Class参数的泛型方法（需要调用者自行处理类型转换，更不安全）
String appName2 = reader.<String>getGenericValue("appName");
// Integer port2 = reader.<Integer>getGenericValue("port"); // 编译通过，但如果实际值不是Integer，运行时会报错
System.out.println("App Name 2: " + appName2);

public class EmployeeInfo {
    private String name;
    private int age;

    public EmployeeInfo(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }
}

public class EmployeeService {
    public EmployeeInfo getEmployeeDetails(String employeeId) {
        // 模拟从数据库获取数据
        if ("tomJones".equals(employeeId)) {
            return new EmployeeInfo("Tom Jones", 38);
        }
        return null;
    }
}

// 使用示例
EmployeeService service = new EmployeeService();
EmployeeInfo info = service.getEmployeeDetails("tomJones");

if (info != null) {
    String name = info.getName();
    int age = info.getAge();
    System.out.println("Employee Name: " + name);
    System.out.println("Employee Age: " + age);
}