add faq section
Mahmoud Ben Hassine
10 years ago
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---
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layout: docs
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title: FAQ
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prev_section: get-involved/release-notes
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doc: true
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---
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## <a name="1"></a>[1. Why is Easy Rules called the "The stupid Java rules engine"?](#1)
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The goal behind Easy Rules is to provide a lightweight rules engine without features that 80% of application
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do not need. The term "stupid" is actually the perfect term to describe how the engine works: It iterates
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over a set of ordered rules and execute rules when their conditions are met. This what makes it easy to learn use and
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use following the KISS principle.
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## <a name="2"></a>[2. I would like to return a value upon a rule execution, how to do that?](#2)
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By design, rules do not return values. But you can always make your rules return a result after execution. Here is an example:
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```java
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@Rule(name = "my rule")
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public static class MyRule<T> {
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private boolean executed;
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private T result;
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//@Condition
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public boolean when() {
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return true;
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}
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//@Action
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public void then() throws MyException {
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try {
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System.out.println("my rule has been executed");
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result = null; // assign your result here
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executed = true;
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} catch (MyException e) {
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// executed flag will remain false if an exception occurs
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throw e;
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}
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}
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public boolean isExecuted() {
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return executed;
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}
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public T getResult() {
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return result;
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}
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}
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```
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This rule will return a result if it executes successfully. After firing rules, you query the `executed` flag on your
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rule instance and get the execution result.
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## <a name="3"></a>[3. I've registered multiple instances of the same rule with different inputs, but it seems only the first instance is registered. What's happening?](#3)
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Rules have unique names within a rules engine registry. If you register multiple instances of the same rule, only the first instance will be considered.
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Other instances will be ignored since they have the same name. Let's see an example:
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```java
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@Rule(name = "AgeRule",
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description = "Check if person's age is > 18
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and marks the person as adult")
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public class AgeRule {
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private Person person;
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private int adultAge = 18;
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public AgeRule(Person person) {
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this.person = person;
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}
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@Condition
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public boolean isAdult() {
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return person.getAge() > adultAge;
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}
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@Action
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public void markAsAdult(){
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person.setAdult(true);
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System.out.printf(
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"Person %s has been marked as adult.\n",
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person.getName());
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}
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}
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```
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The `Person` type is a simple Pojo having a `name` and `age` fields. Let's register multiple instances of the `AgeRule`:
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```java
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Person tom = new Person("Tom", 20);
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Person david = new Person("David", 18);
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RulesEngine rulesEngine = aNewRulesEngine().build();
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//first run
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AgeRule ageRule = new AgeRule(tom);
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rulesEngine.registerRule(ageRule);
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rulesEngine.fireRules();
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//first run
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ageRule = new AgeRule(david);
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rulesEngine.registerRule(ageRule);
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rulesEngine.fireRules();
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```
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Both Tom and David are adults, so you are expecting to see:
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```
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Person Tom has been marked as adult.
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Person David has been marked as adult.
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```
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But you see only:
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```
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Person Tom has been marked as adult.
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```
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The second rule instance has been ignored at registration time since it has the same name ( "AgeRule" ) as the first instance.
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So how to deal with multiple data using the same rule?
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You have 2 solutions: Either you clear rules after the first run using `rulesEngine.clearRules()`, or register your rule only once,
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vary input using a setter (that you should add to your rule) and re-fire rules:
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```java
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//create persons
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Person tom = new Person("Tom", 20);
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Person david = new Person("David", 18);
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//create a rules engine
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RulesEngine rulesEngine = aNewRulesEngine().build();
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AgeRule ageRule = new AgeRule();
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rulesEngine.registerRule(ageRule);
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//first run
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ageRule.setPerson(tom);
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rulesEngine.fireRules();
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//second run
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ageRule.setPerson(david);
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rulesEngine.fireRules();
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```
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This is more efficient than registering new instances for each new business data input.
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## <a name="4"></a>[4. Is Easy Rules usable with Android?](#4)
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Yes. Thanks to the community, Easy Rules has been made Android compatible since version 1.3
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## <a name="5"></a>[5. Can I use Easy Rules in a web application?](#5)
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Sure. Easy Rules is very lightweight and can be used both in a standalone application or embedded in an application server,
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a servlet container or a dependency injection container.
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## <a name="6"></a>[6. I have another question, how do I do?](#6)
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Feel free to ask your question in the [Gitter](https://gitter.im/benas/easy-rules) channel of the project: [](https://gitter.im/benas/easy-rules?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
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