What do curly braces inside a java property file mean?

Question

We have many property files inside our java project. I don't understand the meaning of the integer values inside the curly braces.
Example:
validation.error=Input Validation Failed for field:[{0}]. Reason:[{1}]

Answer 1

They are for use with the MessageFormat class. Something of the form {n}, where n is a number, is a placeholder for a dynamic value.

There are additional things you can add to the placeholder for formatting purposes; see the linked Javadocs above for more information.

Answer 2

They're placeholders for parameters. When used, two parameters would be passed to indicate the name of the field and the reason for failure.

Answer 3

The curly brackets are placeholders.

You can use placeholders in your messages and replace them with location-appropriate values at runtime based on the semantics of your user's language. For this you use the MessageFormat class.