传递类类型作为参数以在 ArrayList 中使用? [英] Pass class type as parameter to use in ArrayList?

问题描述

我需要编写一个 java 方法，它接受一个类(不是一个对象)，然后创建一个 ArrayList，该类作为数组中每个成员的元素.伪代码示例:

I need to write a java method which takes a class (not an object) and then creates an ArrayList with that class as the element of each member in the array. Pseudo-code example:

public void insertData(String className, String fileName) {
      ArrayList<className> newList = new ArrayList<className>();
}

如何在 Java 中完成此操作?

How can I accomplish this in Java?

推荐答案

您可以使用 泛型方法

public <T> void insertData(Class<T> clazz, String fileName) {
   List<T> newList = new ArrayList<>();
}

但是如果你应该使用这个契约insertData(String className, String fileName)，你不能使用泛型，因为Java无法在编译时解析列表项的类型.

but if you should use this contract insertData(String className, String fileName), you cannot use generics because type of list item cannot be resolved in compile-time by Java.

在这种情况下，您可以根本不使用泛型，而是在将其放入列表之前使用反射来检查类型:

In this case you can don't use generics at all and use reflection to check type before you put it into list:

public void insertData(String className, String fileName) {
    List newList = new ArrayList();

    Class clazz;
    try {
        clazz = Class.forName(className);
    } catch (ClassNotFoundException e) {
        throw new RuntimeException(e); // provide proper handling of ClassNotFoundException 
    }

    Object a1 = getSomeObjectFromSomewhere();

    if (clazz.isInstance(a1)) {
        newList.add(a1);
    }
    // some additional code
}

但是如果没有类的信息，您只能使用 Object，因为您无法在代码中将对象转换为 UnknownClass.

but without information of class you're able use just Object because you cannot cast your object to UnknownClass in your code.

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