java - Java Generics Copy Constructor

Question

I'm wanting to code a copy constructor for a generically defined class. I have an inner class Node, which I am going to use as the nodes for a binary tree. When I pass in a a new Object

public class treeDB <T extends Object> {
    //methods and such

    public T patient; 
    patient = new T(patient2);       //this line throwing an error
    //where patient2 is of type <T>
}

I just don't know how to generically define a copy constructor.

Answer 1

T不能保证它所代表的类将具有必需的构造函数，因此您不能使用new T(..)表单。

我不确定这是否是您需要的，但如果您确定要复制的对象类将具有复制构造函数，那么您可以使用反射

public class Test<T> {

    public T createCopy(T item) throws Exception {// here should be
        // thrown more detailed exceptions but I decided to reduce them for
        // readability

        Class<?> clazz = item.getClass();
        Constructor<?> copyConstructor = clazz.getConstructor(clazz);

        @SuppressWarnings("unchecked")
        T copy = (T) copyConstructor.newInstance(item);

        return copy;
    }
}

//demo for MyClass that will have copy constructor: 
//         public MyClass(MyClass original)
public static void main(String[] args) throws Exception {
    MyClass mc = new MyClass("someString", 42);

    Test<MyClass> test = new Test<>();
    MyClass copy = test.createCopy(mc);

    System.out.println(copy.getSomeString());
    System.out.println(copy.getSomeNumber());
}