After javac is compiled successfully, "cannot be found or the main class cannot be loaded" appears when the class file is run in Java"

  Add a local directory path at the beginning of the classpath, which is represented by.. because there are two paths of DT and tools in Java, add; to separate the paths.

Sometimes Java cannot run after javac is compiled. Generally, the classpath variable is missing.; that is, the current directory is not added. As a result, the compiled bytecode cannot be found during Java running, so you need to add the-classpath option.

Example: Java-classpath.; Hello

// Add the path of the compiled class file to the current directory.