Braincheck

Braincheck is a very simple library that you can used to check invariants in code. It is designed that these invariant checks can be compiled out in production environments either by the JIT or the GWT compiler. Braincheck also super-sources Objects.requireNonNull(...) to call javaemul.internal.InternalPreconditions.checkNotNull(...) so that these guards can be stripped by configuring the compile-time property jre.checks.checkLevel to DISABLED.

Quick Start

The simplest way to use Braincheck is to;

• Review the javadocs.

• Add the BrainCheck dependencies into the build system. i.e.

<dependency>
   <groupId>org.realityforge.braincheck</groupId>
   <artifactId>braincheck</artifactId>
   <version>1.32.0</version>
</dependency>

• If the application is a GWT application, then inherit from org.realityforge.braincheck.BrainCheck in your .gwt.xml for a production build or inherit org.realityforge.braincheck.BrainCheckDev in a development build. You can also explicitly set the configuration properties to control which parts of the application are optimized away during builds. See the configuration properties section below.

• Add invariant checks to your code to verify various conditions.

import static org.realityforge.braincheck.Guards.*;

class MyClass
{
  public void myMethod(int i)
  {
    // Raise an exception if condition (first parameter) is not true
    apiInvariant( () -> i > 0, () -> "You are using the api incorrectly!" );

    // Raise an exception if condition (first parameter) is not true
    invariant( () -> 1 == 1, () -> "Maths has broken down!" );

    // Raise an exception if invariant checks enabled
    fail( () -> "You have reached a failing scenario in the application" );
  }
}

• You can also modify the invariant configuration in tests by setting system property braincheck.environment to development and interacting with the BrainCheckTestUtil class. i.e.

import org.realityforge.braincheck.BrainCheckTestUtil;

class MyTest
{
  @Test
  public void myTest()
  {
    BrainCheckTestUtil.setCheckApiInvariants( true );
    //...
  }
}

Configuration Properties

The following configuration properties can be used to configure BrainCheck. These are mainly used to optimize the size of applications that statically compile code (i.e. GWT) when we want to minimize code size.

• braincheck.verbose_error_messages which can be set to true or false and if true, then invariant exception messages will use the supplied message, otherwise no message will be passed to exception.
• braincheck.check_invariants which can be set to true or false and if false, calls to Guards.invariant() and Guards.fail() are ignored.
• braincheck.check_api_invariants which can be set to true or false and if false or if braincheck.check_invariants is false then calls to Guards.apiInvariant() are ignored.
• braincheck.environment which can be set to development or production and defaults to production. If production then the default values for braincheck.verbose_error_messages, braincheck.check_invariants and braincheck.check_api_invariants will be false otherwise they will default to be true.