The Extract Constant refactoring makes your source code easier to read and maintain. It also helps you avoid using hardcoded constants without any explanations 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.
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
public, move the constant to another class, and so on.
Let's introduce a constant for the expression
"string" that occurs twice throughout code.
IntelliJ IDEA extacts the constant and replaces the expression with the constant