为什么我必须使用 java -cp .(类名)而不是java(类名)? [英] Why do I have to use java -cp . (class name) and not java (class name)?

问题描述

我只是好奇为什么在像我这样的系统上，我必须使用 java -cp .只是在终端窗口中使用 java 命令不起作用?

I was just curious why on some systems like mine, I have to utilize java -cp . and simply using the java command in the terminal window doesn't work ?

推荐答案

当您使用 java 命令启动 JVM 时，JVM 的类路径确定如下:

When you are launching a JVM using the java command, the JVM's classpath is determined as follows:

• 如果您使用-jar"选项，则类路径由 JAR 文件本身以及 JAR 文件中的可选类路径"属性组成.

• If you use the "-jar" option, then the classpath consists of the JAR file itself, and together with the optional "Classpath" attribute in the JAR file.

否则，如果您使用-cp"选项，则该选项的值会提供类路径

Otherwise, if you use the "-cp" option, the option's value gives the classpath

否则，如果设置了 CLASSPATH 环境变量，则会给出类路径

Otherwise, if the CLASSPATH environment variable is set, then that gives the classpath

否则，类路径只包含当前目录；即.".

Otherwise, the classpath consists of just the current directory; i.e. ".".

现在你说你必须明确给出-cp".以便 java 命令正确执行您的命令.

Now you say that you have to explicitly give "-cp ." in order for the java command to execute your commands correctly.

最可能的解释是您将 CLASSPATH 环境变量设置为不适当的值.当您运行 java MyClass 时，它会在 CLASSPATH 指定的类路径上查找……并失败.但是，当您添加-cp ."时，您是在说忽略 CLASSPATH 并只查看当前目录".

The most likely explanation is that you have the CLASSPATH environment variable set to something inappropriate. When you run a java MyClass, it will be looking on the classpath specified by CLASSPATH ... and failing. But when you add "-cp .", you are saying "ignore CLASSPATH and just look in the current directory".

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