Error: Selection does not contain a main type

The other answers are all valid, however, if you are still having a problem you might not have your class inside the src folder in which case Eclipse may not see it as part of the project. This would also invoke the same error message you have seen.

I hope you are trying to run the main class in this way, see screenshot:

If not, then try this way. If yes, then please make sure that your class you are trying to run has a main method, that is, the same method definition as below:

public static void main(String[] args) {
    // some code here
}

I hope this will help you.

Right click on the folder where you put your main class then click on Build Path --> Use as Source Folder.

Finally run your main file as java application. Hope this problem will be solved.

If the option 'Use as Source Folder' is not visible then inside the 'Build Path' select the option 'Remove from Build Path'. This will allow 'Use as Source Folder' option to appear in the 'Build Path'.

The entry point for Java programs is the method:

public static void main(String[] args) {
    //Code
}

If you do not have this, your program will not run.