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| <td class="back"><a id="top"></a><a href="s6.1.html" rel="prev"><< §6.1 Reflection</a></td> |
| <td class="top"><a href="index.html" rel="contents">↑ Table of Contents ↑</a></td> |
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| <div class="breadcrumb"><a class="nav" href="s6.html" rel="section">§6 Object Teams API</a></div> |
| <div class="sect depth2" id="s6.2"> |
| <h2 class="sect">§6.2 Other API Elements<a class="img" href="s6.2.html" |
| title="PermaLink to §6.2 Other API Elements"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h2> |
| <div class="subsect depth3" id="s6.2.a"> |
| <h4 class="subsect">(a) <span class="title">Interfaces for role encapsulation</span><a class="img" href="s6.2.a.html" |
| title="PermaLink to (a) Interfaces for role encapsulation"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>A set of pre-defined types exist that do <span class="underline">not</span> extend <code>java.lang.Object</code> |
| and have <span class="underline">no</span> features except the operators <code>==</code> and <code>!=</code>. |
| |
| </p> |
| <div class="note"> |
| <h5>Note:</h5> |
| The JLS defines that each interface declares all methods defined in <code>java.lang.Object</code> |
| (<a href="http://java.sun.com/docs/books/jls/second_edition/html/interfaces.doc.html#32392" |
| class="ext">JLS §9.2</a>) |
| and also each object referenced by an interface type can be widened to <code>java.lang.Object</code>. |
| Compilers commonly implement this by declaring <code>java.lang.Object</code> the super-type of all interfaces. |
| Such implementation has no visible difference with respect to the more complex definition in the JLS. |
| |
| </div> |
| <p>These predefined types are |
| |
| </p> |
| <dl> |
| <dt><code>org.objectteams.IConfined</code></dt> |
| <dd>regular interface</dd> |
| <dt><code>org.objectteams.ITeam.IConfined</code></dt> |
| <dd>role interface</dd> |
| <dt><code>org.objectteams.Team.Confined</code></dt> |
| <dd>role class</dd> |
| </dl> |
| <p>These types provide no new functionality but inheriting from these types influences the semantics with respect to encapsulation. |
| |
| The purpose and usage of these types is described in <a href="s7.html" title="§7 Role Encapsulation" class="sect">§7</a>. |
| |
| </p> |
| </div> |
| <div class="subsect depth3" id="s6.2.b"> |
| <h4 class="subsect">(b) <span class="title">Interface for explicit lowering</span><a class="img" href="s6.2.b.html" |
| title="PermaLink to (b) Interface for explicit lowering"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>The following role interface exists for the purpose of allowing explicit lowering: |
| |
| </p> |
| <dl> |
| <dt><code>org.objectteams.ITeam.ILowerable</code></dt> |
| <dd>role interface</dd> |
| </dl> |
| <p>This interface was introduced in detail in <a href="s2.2.d.html" title="§2.2.(d) Explicit lowering" |
| class="sect">§2.2.(d)</a>. |
| |
| </p> |
| </div> |
| <div class="subsect depth3" id="s6.2.c"> |
| <h4 class="subsect">(c) <span class="title">Team activation methods</span><a class="img" href="s6.2.c.html" |
| title="PermaLink to (c) Team activation methods"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>Every team can be activated and deactivated by predefined methods of the interface <code>org.objectteams.ITeam</code>. |
| |
| </p> |
| <dl> |
| <dt><code>activate()</code> and <code>activate(Thread th)</code></dt> |
| <dd>Methods for activation of a team</dd> |
| <dt><code>deactivate()</code> and <code>deactivate(Thread th)</code></dt> |
| <dd>Methods for deactivation of a team</dd> |
| </dl> |
| <p>The usage of these Methods is described in <a href="s5.2.b.html" title="§5.2.(b) Imperative activation" |
| class="sect">§5.2.(b)</a>. |
| |
| </p> |
| </div> |
| <div class="subsect depth3" id="s6.2.d"> |
| <h4 class="subsect">(d) <span class="title">Exceptions</span><a class="img" href="s6.2.d.html" title="PermaLink to (d) Exceptions"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>The following <code>Exceptions</code> can be thrown during the execution of an ObjectTeam/Java program: |
| |
| </p> |
| <dl> |
| <dt><code>ResultNotProvidedException</code></dt> |
| <dd>Thrown if a replace callin without a base call does not provide the necessary (primitive type) base result |
| (see <a href="s4.3.e.html" title="§4.3.(e) Fragile callin binding" |
| class="sect">§4.3.(e)</a>). |
| </dd> |
| <dt><code>LiftingFailedException</code></dt> |
| <dd>Thrown if an actual ambiguity occurs during lifting (see <a href="s2.3.4.c.html" title="§2.3.4.(c) Actual ambiguity" |
| class="sect">§2.3.4.(c)</a>). |
| </dd> |
| <dt><code>WrongRoleException</code></dt> |
| <dd>Thrown during lifting if the base object has, with respect to the same team instance, previously been lifted |
| to a role type that is not conform to the currently requested type |
| (see <a href="s2.3.4.d.html" title="§2.3.4.(d) Mismatching role" |
| class="sect">§2.3.4.(d)</a> and <a href="s2.4.3.html" |
| title="§2.4.3 Role creation in the presence of smart lifting" |
| class="sect">§2.4.3</a>). |
| </dd> |
| <dt><code>DuplicateRoleException</code></dt> |
| <dd>Thrown during explicit role creation, if a new role is created for a base object, which already has a role |
| of the required type in the given team (see <a href="s2.4.1.c.html" |
| title="§2.4.1.(c) Duplicate role runtime check" |
| class="sect">§2.4.1.(c)</a>). |
| </dd> |
| <dt><code>RoleCastException</code></dt> |
| <dd>Thrown during cast of an externalized role, if the casted expression is anchored to a different team instance |
| than the cast type (see <a href="s1.2.4.b.html" title="§1.2.4.(b) Casting" class="sect">§1.2.4.(b)</a>). |
| </dd> |
| <dt><code>LiftingVetoException</code></dt> |
| <dd>This exception is used internally to abort the process of lifting when a relevant guard predicate (<a href="s5.4.html" title="§5.4 Guard predicates" class="sect">§5.4</a>) evaluated to false. |
| Such exceptions thrown from generated code will never appear in client code, so there is usually no need to catch a <code>LiftingVetoException</code>. |
| However, in some situations it is useful to explicitly <em>throw</em> a <code>LiftingVetoException</code> from a lifting constructor (<a href="s2.3.1.b.html" |
| title="§2.3.1.(b) Default lifting constructor" |
| class="sect">§2.3.1.(b)</a>) of a role. |
| This style allows to abort lifting even after the lifting constructor has started to work and also for method parameters |
| requiring lifting. |
| If lifting was triggered due to a callin method binding, this binding will simply not trigger if a <code>LiftingVetoException</code> is thrown |
| while preparing the call to the role method. |
| </dd> |
| </dl> |
| </div> |
| <div class="subsect depth3" id="s6.2.e"> |
| <h4 class="subsect">(e) <span class="title">Role migration</span><a class="img" href="s6.2.e.html" title="PermaLink to (e) Role migration"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>The following interfaces can be used to enable role migration:</p> |
| <dl> |
| <dt><code>IBaseMigratable</code></dt> |
| <dd>This interface declares a method |
| <div class="listing plain"><pre> |
| <code><B> <b>void</b> migrateToBase(B otherBase)</code> </pre></div> |
| and instructs the compiler to generate an implementation of this method |
| for any bound role declaring <code>IBaseMigratable</code> as its super-interface.<br /> |
| The effect of calling <code>migrateToBase</code> on a role instance is to re-bind this role to a new base instance. |
| The base instance must be compatible to the role's base class (in order to avoid problems during lifting the |
| compiler may require the base to be of the exact type of the role's base class). |
| Passing <code>null</code> to this method causes an <code>NullPointerException</code> to be thrown. |
| </dd> |
| <dt><code>ITeamMigratable</code></dt> |
| <dd>This interface declares a method |
| <div class="listing plain"><pre> |
| <code><R> R<@otherTeam> migrateToTeam(<b>final</b> ITeam otherTeam)</code></pre></div> |
| and instructs the compiler to |
| generate an implementation of this method for any role declaring <code>ITeamMigratable</code> as its super-interface.<br /> |
| The effect of calling <code>migrateToTeam</code> on a role instance is to re-bind this role to become a contained part of a new team instance. |
| The team instance must be of the exact type of the role's enclosing team. |
| Passing <code>null</code> to this method causes a <code>NullPointerException</code> to be thrown.<br /><div class="note"> |
| <h5>Caveat:</h5> |
| This method intentionally breaks the rules of family polymorphism: any reference <code>R<@previousTeam> r</code> |
| which was established before migration will incorrectly imply that the role's enclosing team still is <code>previousTeam</code>, |
| which is no longer true after migration. |
| While this does not effect any method lookup (which is still safe), further assumptions based on a role's dependent type |
| are invalidated by team migration. The same holds for references from the migrating role to any sibling role instances.<br /> |
| If the rules of family polymorphism should be maintained one should just refrain from declaring <code>ITeamMigratable</code> |
| as a role's super-interface. |
| </div> |
| </dd> |
| </dl> |
| <p>For both methods the signature declared in the interface is over-generalized, yet the compiler performs the necessary checks |
| to |
| ensure that role, base and team instances are indeed compatible and additionally the return type of <code>migrateToTeam</code> |
| is checked as a self-type, i.e., it reflects the exact type of the call target. |
| </p> |
| </div> |
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