Explicit class declaration can be converted into a compact source file

Reports ordinary classes, which can be converted into compact source files

Example:

  public class Sample {
      public static void main(String[] args) {
          System.out.println("Hello, world!");
      }
  }

After the quick-fix is applied:

  void main() {
      IO.println("Hello, world!");
  }

Locating this inspection

By ID

Can be used to locate inspection in e.g. Qodana configuration files, where you can quickly enable or disable it, or adjust its settings.

ExplicitToImplicitClassMigration

Via Settings dialog

Path to the inspection settings via IntelliJ Platform IDE Settings dialog, when you need to adjust inspection settings directly from your IDE.

Configure the inspection:

Select Replace 'System.out.print()' and 'System.out.println()' with methods from 'java.lang.IO' class to convert these calls to IO methods.

This inspection depends on the Java feature 'Compact source files', which is available since Java 21-preview.

Inspection ID: ExplicitToImplicitClassMigration

New in 2024.1

Inspection options

Here you can find the description of settings available for the Explicit class declaration can be converted into a compact source file inspection, and the reference of their default values.

Replace 'System.out.print()' and 'System.out.println()' with methods from 'java.lang.IO' class

Option ID:

convertToIo

Default value:

Selected

Suppressing Inspection

You can suppress this inspection by placing the following comment marker before the code fragment where you no longer want messages from this inspection to appear:

//noinspection ExplicitToImplicitClassMigration

More detailed instructions as well as other ways and options that you have can be found in the product documentation:

IntelliJ IDEA 2025.3

Inspection Details
By default bundled with:	IntelliJ IDEA 2025.3, Qodana for JVM 2025.3,

Last modified: 03 December 2025