blocks|key|668503|text|您不必导入与当前类位于同一包中的类。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|668504|另外，请注意GradeBook.java是文件的名称。类的(简单)名称是GradeBook。每个类都应该在一个包中。如果它在com.foo.bar包中，则类名为com.foo.bar.GradeBook，这是您在导入该类时必须使用的名称。|668505|阅读http://download.oracle.com/javase/tutorial/java/package/packages.html以了解有关包的更多信息。|offset|length|668506|entityMap|0|LINK|mutability|MUTABLE|url|http://download.oracle.com/javase/tutorial/java/package/packages.html^0|0|0|2|1X|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@$F|S|G|T|1|U]]|A|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]]]

You don't have to import classes that are in the same package as the current class.

Also, note that GradeBook.java is the name of the file. The (simple) name of the class is GradeBook. Every class should be in a package. If it is in the package com.foo.bar, the class name is com.foo.bar.GradeBook, and this is the name you must use when importing this class.

Read <a href="http://download.oracle.com/javase/tutorial/java/package/packages.html" rel="nofollow">http://download.oracle.com/javase/tutorial/java/package/packages.html</a> to learn more about packages.

blocks|key|668543|text|这是因为两者都在同一个包(文件夹)中。它们是自动导入的，不需要为此编写import语句。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|668544|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

It is because both are in same package(folder). They are automatically imported no need to write import statement for that.

blocks|key|668574|text|位于同一包中的类不必导入，因为它们彼此可见。您只需对另一个包中的类执行import操作：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|668575|import+java.util.ArrayList;|code-block|syntax|javascript|668576|请注意，您导入的不是文件，而是类。|668577|entityMap^0|Z|6|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

The classes located in the same package do not have to be imported, as they are visible to each other. You simply <code>import</code> a class that is in another package:

<pre><code>import java.util.ArrayList;
</code></pre>

Note that you are not importing the file, but the class.

blocks|key|885824|text|您不必导入同一个包中的类。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|885825|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

You don't have to import classes which are in the same package.

blocks|key|668637|text|嗯，同一个包中的类会自动导入。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|668638|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Well, classes in the same package are automatically imported.

blocks|key|668666|text|导入用于导入不同包中的类。因为您没有为任何一个声明包，所以它们都被放入缺省包中。编译器可以找到它，因为该类位于相同的目录中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|668667|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Imports are for importing classes that are in a different package. Since you didn't declare a package for either they are both put in the default package. The compiler can find it because the class lives in the same directory.

blocks|key|885917|text|它们都在同一个包里。这个tutorial将会比我做的更公正。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|885918|entityMap|0|LINK|mutability|MUTABLE|url|http://download.oracle.com/javase/tutorial/java/package/packages.html^0|C|8|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

They're in the same package. This <a href="http://download.oracle.com/javase/tutorial/java/package/packages.html" rel="nofollow">tutorial</a> will do more justice than I will.

blocks|key|885954|text|Java不像C那样使用includes。相反，java使用称为类路径的概念，即包含java类的资源列表。JVM可以通过名称访问类路径上的任何类，因此，如果您可以扩展类并只需声明它们就可以引用类型。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|885955|来自：Include+one+java+file+in+another+java+file|offset|length|885956|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/880662/include-one-java-file-in-another-java-file^0|0|3|16|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

Java doesn't use includes the way C does. Instead java uses a concept called the classpath, a list of resources containing java classes. The JVM can access any class on the classpath by name so if you can extend classes and refer to types simply by declaring them.

From: <a href="https://stackoverflow.com/questions/880662/include-one-java-file-in-another-java-file">Include one java file in another java file</a>

I am currently learning Java using the Deitel's book Java How to Program 8th edition (early objects version).

I am on the chapter on creating classes and methods.

However, I got really confused by the example provided there because it consists of two separate .java files and when one of them uses a method from the other one, it did not import the class. It just created an object of that class from the other .java file without importing it first. 

How does that work? Why don't I need to import it?

Here is the code from the book (I removed most comments, to save typing space/time...):
.java class:

<pre><code>//GradeBook.java

public class GradeBook
{
 public void displayMessage()
 {
 System.out.printf( "Welcome to the grade book!" );
 }
}
</code></pre>

The main .java file:

<pre><code>//GradeBookTest.java

public class GradeBookTest
{
 public static void main( String[] args)
 {
 GradeBook myGradeBook = new GradeBook();
 myGradeBook.displayMessage(); 
 }
}
</code></pre>

I thought I had to write 

<pre><code>import GradeBook.java;
</code></pre>

or something like that.
How does the compiler know where GradeBook class and its methods are found and how does it know if it exists at all if we dont import that class?

I did lots of Googling but found no answer.
I am new to programming so please tolerate my newbie question.

Thank you in advance.

Why don't I have to import a class I just made to use it in my main class? (Java)

编译器

Java

我目前正在使用Deitel的书Java How to Program第8版(早期对象版本)学习Java。我正在写关于创建类和方法的章节。但是，我真的被那里提供的示例搞糊涂了，因为它由两个独立的.java文件组成，并且当其中一个文件使用另一个文件中的方法时，它不会导入类。它只是从另一个.java文件创建了该类的一个对象，...

问为什么我不需要导入一个我刚刚创建的类来在我的主类中使用它呢？(Java)
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