Accessing and using Javaclasses from Unity

I want to use AndroidJavaClasses, such as android.content.SharedPreferences, in unity. However, it gives error because of java plugin. How can i use existing android java classes in my unity project?

For example, I want to use it

AndroidJavaObject jo = new AndroidJavaObject(“java.lang.String”, “some string”);

You can’t. Unity does not use Java. Unity uses Unity Script as its default programming language.