Java Assert – Is It a Good Practice?

assertjava

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 Assert.notNull a lot. Here's an example

public static ParsedSql parseSqlStatement(String sql) {
    Assert.notNull(sql, "SQL must not be null");
}

Here's Another one:

public NamedParameterJdbcTemplate(DataSource dataSource) {
    Assert.notNull(dataSource,
            "The [dataSource] argument cannot be null.");
    this.classicJdbcTemplate = new JdbcTemplate(dataSource);
}

public NamedParameterJdbcTemplate(JdbcOperations classicJdbcTemplate) {
    Assert.notNull(classicJdbcTemplate,
            "JdbcTemplate must not be null");
    this.classicJdbcTemplate = classicJdbcTemplate;
}

FYI, The Assert.notNull (not the assert statement) is defined in a util class as follows:

public abstract class Assert { 
   public static void notNull(Object   object, String   message) {
      if (object == null) {
          throw new IllegalArgumentException  (message);
      }
   }
}

Best Answer

In principle, assertions are not that different from many other run-time checkings.

For example, Java bound-checks all array accesses at run-time. Does this make things a bit slower? Yes. Is it beneficial? Absolutely! As soon as out-of-bound violation occurs, an exception is thrown and the programmer is alerted to any possible bug! The behavior in other systems where array accesses are not bound-checked are A LOT MORE UNPREDICTABLE! (often with disastrous consequences!).

Assertions, whether you use library or language support, is similar in spirit. There are performance costs, but it's absolutely worth it. In fact, assertions are even more valuable because it's explicit, and it communicates higher-level concepts.

Used properly, the performance cost can be minimized and the value, both for the client (who will catch contract violations sooner rather than later) and the developers (because the contract is self-enforcing and self-documenting), is maximized.

Another way to look at it is to think of assertions as "active comments". There's no arguing that comments are useful, but they're PASSIVE; computationally they do nothing. By formulating some concepts as assertions instead of comments, they become ACTIVE. They actually must hold at run time; violations will be caught.

Related Solutions

What Are Assertions in Java and When to Use Them

Assertions (by way of the assert keyword) were added in Java 1.4. They are used to verify the correctness of an invariant in the code. They should never be triggered in production code, and are indicative of a bug or misuse of a code path. They can be activated at run-time by way of the -ea option on the java command, but are not turned on by default.

An example:

public Foo acquireFoo(int id) {
    Foo result = (id > 50) ? fooService.read(id) : new Foo(id);

    assert result != null;

    return result;
}

Java Assert – Is It Good Practice to Use Assert in Java?

The main reason assertions are not used is because they are not enabled by default. Therefore if you have a condition that is important enough to require an assertion you can't rely on assertions being enabled to get the job done.

As other answers have correctly stated they're designed for development-time testing and debugging because they cost nothing if assertions are disabled in production. I think it's better to create explicit tests in your testing framework (e.g. a unit test for edge conditions) than rely on someone enabling assertions while testing.

However a good example I've seen for using assertions is checking private method arguments. Since you control the access to those methods you can check that your own class is using the method correctly while your public methods use more reliable argument checking techniques (annotations, if statements, 3rd-party libraries, etc). That way even if assertions are disabled your method should be protected but developers looking at the source code can see the preconditions for your method and turn assertions on for an extra safety net when working on that class.

Best Answer

Related Solutions

What Are Assertions in Java and When to Use Them

Java Assert – Is It Good Practice to Use Assert in Java?

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