从java中的Generic类获取方法的返回值

Question

我创建了一个父类 Repo，它具有在列表中插入、删除、显示和删除对象的方法。 Repo 是一个泛型类。我为 Repo 创建了一个子类（如 DepartmentRepo 类）并传递了 Department、Employee 等类。我想对传递给 Repo 类的任何类对象执行插入、删除、显示和删除操作。 我需要从java中的Generic类获取方法“get”的返回值。我只能从 Generic 中获取方法名，这里我提到了代码文件

public class Department {
    private long Id;
    private String Name;
    private String Location;
    
    public Department() {
        
    }
    
    public Department(long id, String name, String location) {
        super();
        Id = id;
        Name = name;
        Location = location;
    }
    public long getId() {
        return Id;
    }
    public void setId(long id) {
        Id = id;
    }
    public String getName() {
        return Name;
    }
    public void setName(String name) {
        Name = name;
    }
    public String getLocation() {
        return Location;
    }
    public void setLocation(String location) {
        Location = location;
    }
    
    

}

import java.util.ArrayList;
import java.util.List;

public class Repo<T, U> {
    List<T> list = new ArrayList<T>();

    public List<T> getAll() {
        return list;
    }

    public void insert(T obj) {
        list.add(obj);
    }

    public T get(U id) throws NoSuchMethodException, SecurityException {
        for (T ele : list) {
            if (ele.getClass().getMethod("getId") == id) {
                return ele;
            }
        }
        return null;
    }

    public void delete(U id) throws NoSuchMethodException, SecurityException {
        list.remove(get(id));
    }
}

public class DepartmentRepo extends Repo<Department, Long>{

}

class MainApi
{
    public static void main (String[] args)
    {
        DepartmentRepo dept = new DepartmentRepo ();
        Department ict=new Department(10001,"Dept of ICT","Town");
        Department cs=new Department(10002,"Dept of Computer Science","Pampaimadu");
        Department bio=new Department(10003,"Dept of Bio Science","Pampaimadu");
        Department sats=new Department(10004,"Dept of Statistics","Kurumankadu");
        
        dept.insert(ict);
        dept.insert(cs);
        dept.insert(bio);
        dept.insert(sats);
        System.out.println();
        dept.getAll();
        try{
            dept.get(10001);
        }
        catch(Exception e){
            
        }
        
        
    }
}

Answer 1

作为另一种解决方案以及对您评论的回答，您可以使用元素继承，并避免反射调用和异常。

1- 创建一个元素接口或类

public interface RepoElement<U> {
    U getId();
}

或

public class RepoElement<U> {
    private U Id;

    public RepoElement() {}

    public RepoElement(U id) {
        Id = id;
    }

    public U getId() {
        return Id;
    }
    public void setId(U id) {
        Id = id;
    }
}

2- 使Department继承接口OR类

public class Department implements RepoElement<Long> {
    (...)
    public Long getId() {
        return Id;
    }
    (...)
}

或

public class Department extends RepoElement<Long> {
    private String Name;
    private String Location;

    public Department() {
        super();
    }

    public Department(long id, String name, String location) {
        super(id);
        Name = name;
        Location = location;
    }

}

3- 直接在Repo 类中使用（并移除异常）

public class Repo<T extends RepoElement<U>, U> {
    (...)
    public T get(U id) {
        for (T ele : list) {
            if (ele.getId().equals(id)) {
                return ele;
            }
        }
        return null;
    }

    public void delete(U id) {
        list.remove(get(id));
    }
    (...)
}

最后的建议是，您可以在 Repo 类中使用 Map 而不是 List，并摆脱任何搜索复杂性/优化：

public class Repo<T extends RepoElement<U>, U> {
    Map<U, T> map = new HashMap<U, T>();

    public Collection<T> getAll() {
        return map.values();
    }

    public void insert(T obj) {
        map.put(obj.getId(), obj);
    }

    public T get(U id) {
        return map.get(id);
    }

    public void delete(U id) {
        map.remove(id);
    }
}

Answer 2

您需要调用 getId() 方法，以便它返回 id 以正确执行比较：

import java.lang.reflect.InvocationTargetException;
import java.util.ArrayList;
import java.util.List;

public class Repo<T, U> {
    List<T> list = new ArrayList<T>();

    public List<T> getAll() {
        return list;
    }

    public void insert(T obj) {
        list.add(obj);
    }

    public T get(U id) throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
        for (T ele : list) {
            if (ele.getClass().getMethod("getId").invoke(ele).equals(id)) {
                return ele;
            }
        }
        return null;
    }

    public void delete(U id) throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
        list.remove(get(id));
    }
}