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Null object as a singleton iluwatar#50 
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+118
-99
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4 files changed

+118
-99
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‎null-object/etc/test.png‎

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‎null-object/etc/test.ucls‎

Lines changed: 68 additions & 60 deletions
Original file line numberDiff line numberDiff line change
@@ -1,61 +1,69 @@
1-
<?xml version="1.0" encoding="UTF-8"?>
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<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true"
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realizations="true" associations="true" dependencies="false" nesting-relationships="true">
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<interface id="1" language="java" name="com.iluwatar.Node" project="null-object"
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file="/null-object/src/main/java/com/iluwatar/Node.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="535" y="139"/>
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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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</interface>
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<class id="2" language="java" name="com.iluwatar.NodeImpl" project="null-object"
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file="/null-object/src/main/java/com/iluwatar/NodeImpl.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="857" y="348"/>
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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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<class id="3" language="java" name="com.iluwatar.NullNode" project="null-object"
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file="/null-object/src/main/java/com/iluwatar/NullNode.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="535" y="408"/>
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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="4">
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<end type="SOURCE" refId="2" navigable="false">
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<attribute id="5" name="left"/>
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<multiplicity id="6" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="1" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<association id="7">
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<end type="SOURCE" refId="2" navigable="false">
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<attribute id="8" name="right"/>
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<multiplicity id="9" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="1" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<realization id="10">
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<end type="SOURCE" refId="2"/>
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<end type="TARGET" refId="1"/>
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</realization>
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<realization id="11">
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<end type="SOURCE" refId="3"/>
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<end type="TARGET" refId="1"/>
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</realization>
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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"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</classifier-display>
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<association-display labels="true" multiplicity="true"/>
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<?xml version="1.0" encoding="UTF-8"?>
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<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true"
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realizations="true" associations="true" dependencies="false" nesting-relationships="true">
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<class id="1" language="java" name="com.iluwatar.NullNode" project="null-object"
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file="/null-object/src/main/java/com/iluwatar/NullNode.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="123" y="427"/>
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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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<interface id="2" language="java" name="com.iluwatar.Node" project="null-object"
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file="/null-object/src/main/java/com/iluwatar/Node.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="123" y="164"/>
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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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</interface>
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<class id="3" language="java" name="com.iluwatar.NodeImpl" project="null-object"
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file="/null-object/src/main/java/com/iluwatar/NodeImpl.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="399" y="164"/>
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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="4">
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<end type="SOURCE" refId="1" navigable="false">
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<attribute id="5" name="instance"/>
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<multiplicity id="6" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="1" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<realization id="7">
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<end type="SOURCE" refId="1"/>
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<end type="TARGET" refId="2"/>
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</realization>
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<association id="8">
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<end type="SOURCE" refId="3" navigable="false">
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<attribute id="9" name="right"/>
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<multiplicity id="10" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="2" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<realization id="11">
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<end type="SOURCE" refId="3"/>
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<end type="TARGET" refId="2"/>
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</realization>
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<association id="12">
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<end type="SOURCE" refId="3" navigable="false">
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<attribute id="13" name="left"/>
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<multiplicity id="14" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="2" 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"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</classifier-display>
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<association-display labels="true" multiplicity="true"/>
6169
</class-diagram>

‎null-object/src/main/java/com/iluwatar/App.java‎

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -18,14 +18,14 @@ public static void main( String[] args ) {
1818
Node root = new NodeImpl("1",
1919
new NodeImpl("11",
2020
new NodeImpl("111",
21-
new NullNode(),
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new NullNode()),
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new NullNode()),
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NullNode.getInstance(),
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NullNode.getInstance()),
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NullNode.getInstance()),
2424
new NodeImpl("12",
25-
new NullNode(),
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NullNode.getInstance(),
2626
new NodeImpl("122",
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new NullNode(),
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new NullNode())));
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NullNode.getInstance(),
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NullNode.getInstance())));
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root.walk();
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}

‎null-object/src/main/java/com/iluwatar/NullNode.java‎

Lines changed: 44 additions & 33 deletions
Original file line numberDiff line numberDiff line change
@@ -1,33 +1,44 @@
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package com.iluwatar;
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/**
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*
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* Null Object implementation for binary tree node.
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*
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*/
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public class NullNode implements Node {
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@Override
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public int getTreeSize() {
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return 0;
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}
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@Override
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public Node getLeft() {
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return null;
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}
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@Override
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public Node getRight() {
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return null;
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}
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@Override
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public String getName() {
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return null;
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}
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@Override
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public void walk() {
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}
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}
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package com.iluwatar;
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/**
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*
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* Null Object implementation for binary tree node.
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*
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* Implemented as Singleton, since all the NullNodes are the same.
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*
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*/
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public class NullNode implements Node {
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private static NullNode instance = new NullNode();
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private NullNode() {
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}
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public static NullNode getInstance() {
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return instance;
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}
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@Override
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public int getTreeSize() {
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return 0;
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}
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@Override
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public Node getLeft() {
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return null;
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}
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@Override
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public Node getRight() {
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return null;
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}
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@Override
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public String getName() {
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return null;
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}
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@Override
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public void walk() {
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}
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}

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