Short Answer 
To run a Java application, first verify that the file contains a correctly defined main method. Then, set up a run configuration in IntelliJ and ensure the file is part of the project structure, free from syntax errors.
Step 1: Verify the Main Method
Check if the file contains a main method, as it is essential for running Java applications. The main method serves as the entry point for the program and must be defined with the correct signature:
- Must be public
- Should return void
- Must accept a String array as parameters
Step 2: Set Up Run Configuration
Ensure that an appropriate run configuration is created for the file you want to execute. Without this setup, IntelliJ may not know how to run your code. You can create a configuration by:
- Going to the “Run” menu
- Selecting “Edit Configurations”
- Adding a new configuration for your file
Step 3: Check Project Structure and Syntax
Confirm that the file is included in the project structure and is of a runnable type. Additionally, look for any syntax errors that could hinder execution. Pay attention to:
- The file should be a class or interface
- It should not contain compilation issues