Extract constant

The Extract Constant refactoring makes your source code easier to read and maintain. It also helps you avoid usage of hardcoded constants without any explanation about their values or purpose.

In the editor, select an expression or declaration of a variable you want to replace with a constant.
Press Ctrl+Alt+C to introduce a constant or select Refactor | Extract | Constant in the main menu.
Alternatively, on the toolbar that appears, click Extract and select Constant.
By default, IntelliJ IDEA uses the in-place refactoring. To use the Extract Constant dialog for the refactoring, open the Settings dialog (Ctrl+Alt+S) , go to Editor | Code Editing, and select the In modal dialogs refactoring option in the Refactorings area.
Select a name from a list that opens or type your own name and press Enter.
Alternatively, press Ctrl+Alt+C twice to open the Extract Constant dialog where you can specify the additional options for the constant such as making it private or public, move the constant to another class, and so on.
Use mnemonics to quickly change visibility. For example, press Alt to display mnemonics and then press V to change visibility to private

Example

Let's introduce a constant for the expression "string" that occurs twice throughout code.

                            public class Class {
                            public void method() {
                            ArrayList list = new ArrayList();
                            list.add("string");
                            anotherMethod("string");
                            }

                            private void anotherMethod(String string) {
                            }
                            }
                        

IntelliJ IDEA extracts the constant and replaces the expression with the constant STRING.

                            public class Class {
                            private static final String STRING = "string";

                            public void method() {
                            ArrayList list = new ArrayList();
                            list.add(STRING);
                            anotherMethod(STRING);
                            }

                            private void anotherMethod(String string) {
                            }
                            }
                        

Last modified: 08 October 2024