Selection Does Not Contain A Main Type

I'm trying to run a simple code which is to just print out "Hello World", but whenever I run it, a message appears that reads: "Select a way to run Project_1(Which is the Java Project)"

The selections for it are: Java Applet and Java Application.Whenever I click Java Applet it reads: Selection does not contain an applet.When I click Java Application: Selection does not contain a main type.Here is the code which I believe is correct:

package packag_1;
public class Num_1 {
public static void main(String args){
System.out.println("Hello World");
}
}