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iluwatar#95 Updated and clarified Command pattern example
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‎README.md

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -299,7 +299,7 @@ A programming idiom is a means of expressing a recurring construct in one or mor
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## <a name="command">Command</a> [&#8593;](#list-of-design-patterns)
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**Intent:** Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.
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302-
![alt text](https://github.com/iluwatar/java-design-patterns/blob/master/command/etc/command_1.png "Command")
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![alt text](https://github.com/iluwatar/java-design-patterns/blob/master/command/etc/command.png "Command")
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**Applicability:** Use the Command pattern when you want to
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‎command/etc/command.png

-11.4 KB
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‎command/etc/command.ucls

Lines changed: 34 additions & 75 deletions
Original file line numberDiff line numberDiff line change
@@ -3,7 +3,7 @@
33
realizations="true" associations="true" dependencies="false" nesting-relationships="true">
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<class id="1" language="java" name="com.iluwatar.command.ShrinkSpell" project="command"
55
file="/command/src/main/java/com/iluwatar/command/ShrinkSpell.java" binary="false" corner="BOTTOM_RIGHT">
6-
<position height="160" width="141" x="-171" y="634"/>
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<position height="178" width="141" x="-30" y="681"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
@@ -12,7 +12,7 @@
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</class>
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<class id="2" language="java" name="com.iluwatar.command.Goblin" project="command"
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file="/command/src/main/java/com/iluwatar/command/Goblin.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="106" width="138" x="13" y="1069"/>
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<position height="-1" width="-1" x="129" y="1223"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
@@ -21,7 +21,7 @@
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</class>
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<class id="3" language="java" name="com.iluwatar.command.Wizard" project="command"
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file="/command/src/main/java/com/iluwatar/command/Wizard.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="160" width="212" x="91" y="235"/>
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<position height="-1" width="-1" x="129" y="362"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
@@ -30,7 +30,7 @@
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</class>
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<class id="4" language="java" name="com.iluwatar.command.Command" project="command"
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file="/command/src/main/java/com/iluwatar/command/Command.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="159" width="142" x="9" y="435"/>
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<position height="-1" width="-1" x="129" y="561"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
@@ -39,66 +39,58 @@
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</class>
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<class id="5" language="java" name="com.iluwatar.command.InvisibilitySpell" project="command"
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file="/command/src/main/java/com/iluwatar/command/InvisibilitySpell.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="160" width="141" x="10" y="634"/>
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<position height="160" width="141" x="151" y="681"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<enumeration id="6" language="java" name="com.iluwatar.command.Visibility" project="command"
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file="/command/src/main/java/com/iluwatar/command/Visibility.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="178" width="157" x="191" y="1069"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</enumeration>
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<enumeration id="7" language="java" name="com.iluwatar.command.Size" project="command"
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file="/command/src/main/java/com/iluwatar/command/Size.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="196" width="144" x="-171" y="1069"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</enumeration>
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<class id="8" language="java" name="com.iluwatar.command.Target" project="command"
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<class id="6" language="java" name="com.iluwatar.command.Target" project="command"
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file="/command/src/main/java/com/iluwatar/command/Target.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="195" width="176" x="13" y="834"/>
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<position height="-1" width="-1" x="129" y="1014"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<association id="9">
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<association id="7">
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<end type="SOURCE" refId="3" navigable="false">
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<attribute id="8" name="redoStack">
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<position height="20" width="67" x="140" y="451"/>
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</attribute>
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<multiplicity id="9" minimum="0" maximum="2147483647">
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<position height="18" width="25" x="221" y="452"/>
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</multiplicity>
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</end>
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<end type="TARGET" refId="4" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<generalization id="10">
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<end type="SOURCE" refId="2"/>
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<end type="TARGET" refId="6"/>
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</generalization>
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<association id="11">
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<end type="SOURCE" refId="1" navigable="false">
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<attribute id="10" name="target"/>
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<multiplicity id="11" minimum="0" maximum="1"/>
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<attribute id="12" name="target"/>
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<multiplicity id="13" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="8" navigable="true"/>
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<end type="TARGET" refId="6" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<generalization id="12">
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<generalization id="14">
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<end type="SOURCE" refId="1"/>
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<end type="TARGET" refId="4"/>
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</generalization>
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<generalization id="13">
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<bendpoint x="181" y="435"/>
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<bendpoint x="181" y="634"/>
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<end type="SOURCE" refId="3"/>
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<end type="TARGET" refId="8"/>
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</generalization>
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<generalization id="14">
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<end type="SOURCE" refId="2"/>
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<end type="TARGET" refId="8"/>
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</generalization>
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<association id="15">
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<end type="SOURCE" refId="3" navigable="false">
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<attribute id="16" name="undoStack"/>
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<multiplicity id="17" minimum="0" maximum="2147483647"/>
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<attribute id="16" name="undoStack">
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<position height="20" width="70" x="-17" y="451"/>
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</attribute>
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<multiplicity id="17" minimum="0" maximum="2147483647">
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<position height="18" width="25" x="60" y="452"/>
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</multiplicity>
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</end>
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<end type="TARGET" refId="4" navigable="true"/>
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<display labels="true" multiplicity="true"/>
@@ -112,42 +104,9 @@
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<attribute id="20" name="target"/>
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<multiplicity id="21" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="8" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<association id="22">
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<end type="SOURCE" refId="8" navigable="false">
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<attribute id="23" name="visibility"/>
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<multiplicity id="24" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="6" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<association id="25">
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<end type="SOURCE" refId="8" navigable="false">
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<attribute id="26" name="size"/>
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<multiplicity id="27" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="7" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<association id="28">
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<end type="SOURCE" refId="3" navigable="false">
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<attribute id="29" name="redoStack"/>
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<multiplicity id="30" minimum="0" maximum="2147483647"/>
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</end>
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<end type="TARGET" refId="4" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<association id="31">
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<bendpoint x="-162" y="834"/>
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<end type="SOURCE" refId="1" navigable="false">
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<attribute id="32" name="oldSize"/>
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<multiplicity id="33" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="7" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>

‎command/etc/command_1.png

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Binary file not shown.

‎command/src/main/java/com/iluwatar/command/App.java

Lines changed: 47 additions & 36 deletions
Original file line numberDiff line numberDiff line change
@@ -1,36 +1,47 @@
1-
package com.iluwatar.command;
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/**
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*
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* In Command pattern actions are objects that can be executed and undone.
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*
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* In this example the commands are the spells cast by the wizard on the goblin.
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*
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*/
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public class App {
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public static void main(String[] args) {
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Wizard wizard = new Wizard();
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Goblin goblin = new Goblin();
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goblin.printStatus();
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wizard.castSpell(new ShrinkSpell(), goblin);
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goblin.printStatus();
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wizard.castSpell(new InvisibilitySpell(), goblin);
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goblin.printStatus();
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wizard.undoLastSpell();
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goblin.printStatus();
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wizard.undoLastSpell();
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goblin.printStatus();
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wizard.redoLastSpell();
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goblin.printStatus();
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wizard.redoLastSpell();
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goblin.printStatus();
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}
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}
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package com.iluwatar.command;
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/**
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*
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* In Command pattern actions are objects that can be executed and undone.
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*
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* Four terms always associated with the command pattern are command, receiver, invoker and client. A command
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* object (spell) knows about receiver (target) and invokes a method of the receiver. Values for parameters of
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* the receiver method are stored in the command. The receiver then does the work. An invoker object (wizard)
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* knows how to execute a command, and optionally does bookkeeping about the command execution. The invoker
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* does not know anything about a concrete command, it knows only about command interface. Both an invoker object
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* and several command objects are held by a client object (app). The client decides which commands to execute at
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* which points. To execute a command, it passes the command object to the invoker object.
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*
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* In other words, in this example the wizard casts spells on the goblin. The wizard keeps track of the previous
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* spells cast, so it is easy to undo them. In addition, the wizard keeps track of the spells undone, so they
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* can be redone.
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*
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*
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*/
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public class App {
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public static void main(String[] args) {
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Wizard wizard = new Wizard();
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Goblin goblin = new Goblin();
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goblin.printStatus();
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wizard.castSpell(new ShrinkSpell(), goblin);
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goblin.printStatus();
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wizard.castSpell(new InvisibilitySpell(), goblin);
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goblin.printStatus();
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wizard.undoLastSpell();
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goblin.printStatus();
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wizard.undoLastSpell();
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goblin.printStatus();
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wizard.redoLastSpell();
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goblin.printStatus();
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wizard.redoLastSpell();
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goblin.printStatus();
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}
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}

‎command/src/main/java/com/iluwatar/command/Goblin.java

Lines changed: 20 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -1,15 +1,20 @@
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package com.iluwatar.command;
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public class Goblin extends Target {
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public Goblin() {
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setSize(Size.NORMAL);
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setVisibility(Visibility.VISIBLE);
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}
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@Override
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public String toString() {
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return "Goblin";
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}
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}
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package com.iluwatar.command;
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/**
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*
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* Goblin is the target of the spells
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*
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*/
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public class Goblin extends Target {
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public Goblin() {
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setSize(Size.NORMAL);
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setVisibility(Visibility.VISIBLE);
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}
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@Override
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public String toString() {
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return "Goblin";
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}
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}

‎command/src/main/java/com/iluwatar/command/InvisibilitySpell.java

Lines changed: 36 additions & 31 deletions
Original file line numberDiff line numberDiff line change
@@ -1,31 +1,36 @@
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package com.iluwatar.command;
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public class InvisibilitySpell extends Command {
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private Target target;
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@Override
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public void execute(Target target) {
9-
target.setVisibility(Visibility.INVISIBLE);
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this.target = target;
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}
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@Override
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public void undo() {
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if (target != null) {
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target.setVisibility(Visibility.VISIBLE);
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}
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}
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@Override
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public void redo() {
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if (target != null) {
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target.setVisibility(Visibility.INVISIBLE);
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}
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}
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@Override
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public String toString() {
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return "Invisibility spell";
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}
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}
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package com.iluwatar.command;
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/**
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*
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* InvisibilitySpell is a concrete command
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*
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*/
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public class InvisibilitySpell extends Command {
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private Target target;
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@Override
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public void execute(Target target) {
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target.setVisibility(Visibility.INVISIBLE);
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this.target = target;
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}
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@Override
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public void undo() {
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if (target != null) {
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target.setVisibility(Visibility.VISIBLE);
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}
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}
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@Override
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public void redo() {
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if (target != null) {
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target.setVisibility(Visibility.INVISIBLE);
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}
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}
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@Override
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public String toString() {
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return "Invisibility spell";
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}
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}

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