"System.out.println()"会如何处理?在可执行jar中? [英] What happens to "System.out.println()" in executable jar?

问题描述

假设我已经从使用过的代码中创建了executable jar

Suppose I've created an executable jar from a code where I have used

System.out.println()

当我们运行可执行jar时，没有控制台.那么，这条线怎么办? java如何处理这种情况?

When we run the executable jar, there is no console. So, what happens to this line? How does java handle this situation?

编辑01 :

注意:这种情况是当我不使用控制台来运行jar或将其与任何控制台相关联时.

NOTE: The situation is when I don't use a console to run the jar nor associate any console with it anyhow.

EDIT 02 :使事情更清晰:

我知道什么都不会打印，因为没有控制台..！我想知道在这种情况下java如何处理这一行?生成可执行jar的字节码时，是否会省略此行?还是在没有控制台的情况下忽略了这条线?还是什么...

I know that nothing will be printed anywhere as there is no console..! I want to know how java handle this line in this case? Is this line omitted when generating the bytecode for a executable jar? Or is this line just overlooked when there is no console? Or anything...

推荐答案

在可执行jar文件中运行代码没有什么特别之处.如果您是从控制台运行的，例如使用java -jar foo.jar，输出仍将转到控制台.

There's nothing special about running code in an executable jar file. If you run it from a console, e.g. with java -jar foo.jar the output will still go to the console.

如果您以某种不附加控制台的方式运行代码(例如Windows上的javaw，这是与可执行jar文件相关联的默认程序)，则输出将无处可去.它不会引起任何错误-文本只会丢失.

If you run the code in some way that doesn't attach a console - such as javaw on Windows, which is the default program associated with executable jar files - then the output won't go anywhere. It won't cause any errors - the text will just be lost.

请注意，在这种情况下，如果改用System.console()，则 that 将返回null.所以:

Note that in that case, if you use System.console() instead, that will return null. So:

System.out.printf("Foo%n"); // No problem. Goes nowhere.
System.console().printf("Foo%n"); // Would throw a NullPointerException.

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