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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<div class="section"><h2>Working with objects of any type (generic operators)<a name="Working_with_objects_of_any_type_generic_operators"></a></h2><p>A <i>generic operator</i> is what you will get when creating an expression (<tt>Op.on(...)</tt> or <tt>Fn.on(...)</tt>) on any object which is not an array, a list, a map or a set. This is, an operator which will let you execute actions on your objects, but not offer any special built-in features like iterating with <i>forEach()</i>.</p><ul><li><a href="#a1">Creating generic expressions</a></li><li><a href="#a2">Returning results</a></li><li><a href="#a3">Converting to arrays, lists, sets or maps</a></li><li><a href="#a4">Executing functions</a></li><li><a href="#a5">Selecting (conditional code)</a></li><li><a href="#a6">Replacing</a></li></ul><div class="section"><h3><a name="a1">1</a>. Creating generic expressions<a name="a1._Creating_generic_expressions"></a></h3><div class="section"><h4>Operation expressions<a name="Operation_expressions"></a></h4><p>Generic operation expressions are created on an object which is neither an array, nor a list, map or set:</p><div class="source"><pre>Op.on(object)...
</pre></div><p>Also, any operator on arrays, lists, maps or sets can be turned into a generic operator by executing the <i>generic()</i> action:</p><div class="source"><pre>Op.onList(...).generic().[GENERIC ACTIONS]...
</pre></div></div><div class="section"><h4>Function expressions<a name="Function_expressions"></a></h4><p>Function expressions are created by specifying the input type:</p><div class="source"><pre>// Create a function which receives a String variable as input
function = Fn.on(Types.STRING)...get();
</pre></div></div></div><div class="section"><h3><a name="a2">2</a>. Returning results<a name="a2._Returning_results"></a></h3><p>Generic operators, as all others, return their results by means of the <tt>get()</tt> action:</p><div class="source"><pre>newObject = Op.on(object)...get();
</pre></div></div><div class="section"><h3><a name="a3">3</a>. Converting to arrays, lists, sets or maps<a name="a3._Converting_to_arrays_lists_sets_or_maps"></a></h3><p>Generic operators can convert their targets into <i>singleton</i> arrays, lists, sets or maps. This means creating one of these structures and then adding only one element (the target) to them.</p><div class="section"><h4>Arrays<a name="Arrays"></a></h4><p>For creating a singleton array:</p><div class="source"><pre>String[] array = Op.on(str).intoSingletonArrayOf(Types.STRING).get();
</pre></div></div><div class="section"><h4>Lists<a name="Lists"></a></h4><p>For creating a singleton list:</p><div class="source"><pre>List<String> list = Op.on(str).intoSingletonList().get();
</pre></div></div><div class="section"><h4>Sets<a name="Sets"></a></h4><p>For creating a singleton set:</p><div class="source"><pre>Set<String> set = Op.on(str).intoSingletonSet().get();
</pre></div></div><div class="section"><h4>Maps<a name="Maps"></a></h4><p>Maps are a little bit trickier, because each <i>element</i> of a map (a <i>map entry</i>) is in fact composed of two objects instead of one: a <i>key</i>, and a <i>value</i>.</p><p>That is why, in order to obtain a map with a single entry from the generic operator's target, we will have to either apply a <i>map builder</i> function, or simply add (<i>zip</i>) another object as key or value. </p><div class="section"><h5>Using a Map Builder<a name="Using_a_Map_Builder"></a></h5><p>A Map Builder is an function which returns map entries (<tt>IFunction<T,Map.Entry<K,V>></tt>), usually created by extending the abstract class <tt>org.op4j.functions.MapBuilder</tt>, and which provides op4j with a way of creating a map entry from each of the list's elements.</p><p><tt>MapBuilder</tt> looks like this:</p><div class="source"><pre>public abstract class MapBuilder<T,K,V> implements IFunction<T,Map.Entry<K,V>> {
public abstract K buildKey(final T target);
public abstract V buildValue(final T target);
...
}
</pre></div><p>Let's use it for creating our singleton map: </p><div class="source"><pre>MapBuilder<String,Integer,Calendar> mapBuilder = ...;
Map<Integer,Calendar> map = Op.on(str).intoSingletonMap(mapBuilder).get();
</pre></div></div><div class="section"><h5>Zipping key or value<a name="Zipping_key_or_value"></a></h5><p>The singleton map can also be created by zipping. This means either considering the generic operator's target object as a key and then adding (zipping) a value, or the opposite.</p><p>Let's add the value:</p><div class="source"><pre>// map = {{1="a"}}
Map<Integer,String> map = Op.on(1).zipValue("a").get();
</pre></div><p>Or the contrary:</p><div class="source"><pre>// map = {{"a"=1}}
Map<String,Integer> map = Op.on(1).zipKey("a").get();
</pre></div><p>Alternatively, a function can be used for evaluating the target object and obtaining the zipped key or value:</p><div class="source"><pre>IFunction<Integer,String> valueEvaluatorFn = ...;
Map<Integer,String> map = Op.on(1).zipValueBy(valueEvaluatorFn).get();
</pre></div><div class="source"><pre>IFunction<Integer,String> keyEvaluatorFn = ...;
Map<String,Integer> map = Op.on(1).zipKeyBy(keyEvaluatorFn).get();
</pre></div></div></div></div><div class="section"><h3><a name="a4">4</a>. Executing functions<a name="a4._Executing_functions"></a></h3><p>In generic operators, functions are executed the usual way:</p><div class="source"><pre>String upperStr = Op.on("a String").exec(FnString.toUpperCase()).get();
</pre></div><p>A condition can be added for <i>null-saving</i> a function execution, if needed:</p><div class="source"><pre>String upperStr = Op.on(str).execIfNotNull(FnString.toUpperCase()).get();
</pre></div></div><div class="section"><h3><a name="a5">5</a>. Selecting (conditional code)<a name="a5._Selecting_conditional_code"></a></h3><p>op4j allows the conditional execution of actions. Once the condition (an action starting with "<tt>if</tt>") is executed, all subsequent actions will apply only on the target object only if it has been selected (condition was true).</p><p>For example, lets convert into upper case only if the String value is not "uncapitalizable".</p><div class="source"><pre>String upper =
Op.on(str).ifTrue(FnString.notEq("uncapitalizable")).exec(FnString.toUpperCase()).get();
</pre></div><p>As usual, selections can be ended with <tt>endIf(...)</tt>:</p><div class="source"><pre>Op.on(...).ifTrue(...).[ACTIONS ON SELECTED ELEMENTS].endIf()...
</pre></div><div class="section"><h4>Types of selection actions<a name="Types_of_selection_actions"></a></h4><p>Selection can be based on the nullity of the target: </p><div class="source"><pre>Op.on(...).ifNull()....
Op.on(...).ifNotNull()....
</pre></div><p>And also on the value returned by the evaluation of a function returning <tt>Boolean</tt>:</p><div class="source"><pre>IFunction<T,Boolean> eval = ...;
...
Op.on(...).ifTrue(eval)...
Op.on(...).ifFalse(eval)...
</pre></div></div><div class="section"><h4>Restricions on execution actions after selection<a name="Restricions_on_execution_actions_after_selection"></a></h4><p>After executing a selection action, function executed by means of an <i>exec</i> action cannot change the operator type.</p><p>So this would not be valid:</p><div class="source"><pre>// Will not compile!
Integer intObj =
Op.on(str).ifTrue(FnString.notEq("-")).exec(FnString.toInteger()).get();
</pre></div><p>...because converting the operator target only <i>sometimes</i> (if some condition is true) means that the real type of the target object cannot be known after executing.</p></div></div><div class="section"><h3><a name="a6">6</a>. Replacing<a name="a6._Replacing"></a></h3><p>Operator targets can be replaced by other objects:</p><div class="source"><pre>String newString =
Op.on(str).ifNull().replaceWith("[no value]").get();
</pre></div><p>...which is equivalent to:</p><div class="source"><pre>String newString =
Op.on(str).replaceIfNotNullWith("[no value]").get();
</pre></div></div></div>
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