Assert a good practice or not?

Question

Is it a good practice to use Assert for function parameters to enforce their validity. I was going through the source code of Spring Framework and I noticed that they use

Answer 1

Those asserts are library-supplied and are not the same as the built-in assert keyword.

There's a difference here: asserts do not run by default (they must be enabled with the -ea parameter), while the assertions provided by the Assert class cannot be disabled.

In my opinion (for what it's worth), this is as good a method as any for validating parameters. If you had used built-in assertions as the question title implies, I would have argued against it on the basis that necessary checks should not be removable. But this way is just shorthand for:

public static ParsedSql parseSqlStatement(String sql) {
    if (sql == null)
        throw new IllegalArgumentException("SQL must not be null");
    ...
}

... which is always good practice to do in public methods.

The built-in style of asserts is more useful for situations where a condition should always be true, or for private methods. The language guide introducing assertions has some good guidelines which are basically what I've just described.