import java.util.*; 和 import java.util.* 有什么区别？并导入 java.util.stream;?
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What's the difference between import java.util.*; and import java.util.stream;?
提问by Adam
I'm using Java 8's Streamfunctionality to manipulate the contents of an array in my program:
我正在使用 Java 8 的Stream功能在我的程序中操作数组的内容：
Obstacle[] closestObstacles = Stream.generate(() -> new Obstacle()).limit(8).toArray(Obstacle[]::new); // one for each line of attack
When I try importing Streamlike this: import java.util.*;I get a "the symbol Stream cannot be resolved" error. When I instead import Streamlike this: java.util.stream;things work as expected. Why does this happen? I don't use Streamor anything named "stream" elsewhere in my program, so I don't think it's a name conflict?
当我尝试Stream像这样导入时：import java.util.*;我收到“无法解析符号流”错误。当我Stream像这样导入时：java.util.stream;事情按预期工作。为什么会发生这种情况？我没有Stream在程序的其他地方使用或任何名为“stream”的东西，所以我认为这不是名称冲突？
回答by Turing85
I doubt that your second attempt (import java.util.stream;) works. As @JonSkeet pointed out, it should result in a compilation error: error: cannot find symbol. Maybe you wanted to import java.util.stream.*;?
我怀疑您的第二次尝试 ( import java.util.stream;) 是否有效。作为@JonSkeet指出，应该导致编译错误：error: cannot find symbol。也许你想import java.util.stream.*;？
To your actual question:
If you import with a wildcard, that is the asterisk (*) character, only the direct classes in this package will be imported, not the classes in sub-packages. Thus with an import java.util.*, you import classes like ArrayList, LinkedListand Random. A full list can be found here. The class Streamactually resides in the sub-package java.util.streampackage and is not imported when you import java.util.*;.
对于您的实际问题：
如果您使用通配符导入，即星号 ( *) 字符，则只会导入此包中的直接类，而不导入子包中的类。因此，使用import java.util.*，您可以导入诸如ArrayList,LinkedList和 之类的类Random。可以在此处找到完整列表。该类Stream实际上驻留在子java.util.stream包包中，并且在您import java.util.*;.
To import Stream, you can either import java.util.stream.*;(all classes within this package) or only import java.util.stream.Stream;(the FQDN of the class you need).
要导入Stream，您可以import java.util.stream.*;（此包中的所有类）或仅import java.util.stream.Stream;（您需要的类的 FQDN）。
