如何从类的字符串表示形式转换为该类的实例？

Question

I have a string representation of a class's path. It could be any of three classes, all of which implement the same interface, Adapter , but I don't know what the value is.

• "com.example.adapters.Music"
• "com.example.adapters.Video"
• "com.example.adapters.Photo"

Given only a variable holding one of the three strings above, how can I get a usable instance of the actual class?

Answer 1

You can use:

String name = "com.example.adapters.Music";
Object obj = Class.forName(name).newInstance();

You will then have to cast obj to the correct type (possibly by examining the name or by using instanceof ). It is easier if your classes have a common base class (or interface that they implement) and you can use obj knowing only that it is some subclass.

This will only work if the class has a default constructor. Otherwise you will have to use reflection to get an instance of a constructor method and invoke it with the proper arguments.

Answer 2

If a class has a no-argument constructor, then creating an object from its package-qualified class name (for example, "java.lang.Integer") is usually done using these methods:

Class.forName
Class.newInstance


For e.g MusicClass mObj = Class.forName(<string name>).newInstance();

If arguments need to be passed to the constructor, then these alternatives may be used instead:

Class.getConstructor
Constructor.newInstance

Answer 3

您可以使用String数组保存三个字符串

String names[]= {"com.example.adapters.Music","com.example.adapters.Video","com.example.adapters.Photo"};