java如何使用其他包中的类？

Question

我可以导入，使用其他包中的类吗？ 在 Eclipse 中，我做了 2 个包 一个是主要的，另一个是次要的

main
 -main (class)
second
 -second (class)

and I wanted the main function of main class to call the function x in second class. how can I do it? I tried:

import second; 
second.x(); (if both classes are in the same package then it works)
second.second.x();

但他们都没有工作。 我现在想不通了。

Answer 1

您必须提供要导入的完整路径。

import com.my.stuff.main.Main;
import com.my.stuff.second.*;

So, in your main class, you'd have:

package com.my.stuff.main

import com.my.stuff.second.Second;   // THIS IS THE IMPORTANT LINE FOR YOUR QUESTION

class Main {
   public static void main(String[] args) {
      Second second = new Second();
      second.x();  
   }
}

EDIT: adding example in response to Shawn D's comment

There is another alternative, as Shawn D points out, where you can specify the full package name of the object that you want to use. This is very useful in two locations. First, if you're using the class exactly once:

class Main {
    void function() {
        int x = my.package.heirarchy.Foo.aStaticMethod();

        another.package.heirarchy.Baz b = new another.package.heirarchy.Bax();
    }
}

或者，当您想要区分具有相同短名称的两个类时，这很有用:

class Main {
    void function() {
        java.util.Date utilDate = ...;
        java.sql.Date sqlDate = ...;
    }
}