Command Java could not find or load the main class

This is due to the use of the package caused by CMD cannot find the class file generated errors, the solution:
Method 1. Remove the first line of package demo1 in the Helloword.java source program, then use Javac Helloword.java to generate the class file under CMD, and Java HelloWorld run the program

Method 2. Under the project, create a new folder with the same package as the package demo1, place the Helloword.java under the Demo1 folder; cmd to the directory sibling to the Demo1 folder , run Javac demo1/ Helloword.java Compile the program, and then run Java demo1. Helloword can run Java programs that contain DEMO1 package names

Command Java could not find or load the main class