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<section version="5.0" xml:id="sd1_exam_2023_summer" xml:lang="en"
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<title>SD1 examination summer 2023</title>
<section xml:id="sd1_exam_2023_summer_task1">
<title>Implementing tasks</title>
<section xml:id="sd1_exam_2023_summer_task1_preparation">
<title>Preparation</title>
<orderedlist>
<listitem>
<para>Download and unzip the above file
<filename>exam.zip</filename>. You should see a directory
»<filename>Exam</filename>« containing a
<filename>pom.xml</filename> file.</para>
</listitem>
<listitem>
<para>Open this project in your <productname>IDEA</productname> IDE
by selecting the <filename>Exam/pom.xml</filename> file.</para>
</listitem>
</orderedlist>
</section>
<section xml:id="sd1_exam_2023_summer_task1_task">
<title>Task</title>
<qandaset defaultlabel="qanda" xml:id="sd1_exam_2023_summer_task1Qanda">
<qandadiv>
<qandaentry>
<question>
<para>Open the <filename>Readme.md</filename> file in your
project's root. It contains all necessary instructions for
solving the implementation tasks.</para>
</question>
<answer>
<para>Solution see <link
xlink:href="https://gitlab.mi.hdm-stuttgart.de/goik/GoikLectures/-/tree/master/Klausuren/Sd1/2023summer/Solve">summer
2023 exam</link>.</para>
</answer>
</qandaentry>
</qandadiv>
</qandaset>
</section>
<section xml:id="sd1_exam_2023_summer_task1Caveats">
<title>Caveats</title>
<itemizedlist>
<listitem>
<para>When approaching end of examination check your input for
completeness prior to being automatically logged out by the system.
Remember: There is 120 minutes for the examination and another 5
minutes to check for completeness.</para>
</listitem>
<listitem>
<para>Projects residing just on your local workstation's file system
cannot be recovered after finishing the exam.</para>
</listitem>
</itemizedlist>
</section>
</section>
<section xml:id="sd1_exam_2023_summer_task2">
<title>switch versus if ... else if ... else</title>
<qandaset defaultlabel="qanda" xml:id="sd1_exam_2023_summer_task3Qanda">
<qandadiv>
<qandaentry>
<question>
<para>Consider a method
<methodname>computeItemCount()</methodname> of following
signature:</para>
<programlisting language="none">static int computeItemCount() {...}</programlisting>
<para>This method will be called by two different implementations
of another method <methodname>getScore()</methodname>:</para>
<informaltable border="1">
<tr>
<th>Implementation by <code>switch</code></th>
<th>Implementation by <code>if ... else if ...
else</code></th>
</tr>
<tr>
<td valign="top"><programlisting language="java">public static int getScore() {
switch (computeItemCount()){
case 1: return 20;
case 3: return 50;
default: return 0;
}
}</programlisting></td>
<td valign="top"><programlisting language="java">public static int getScore() {
if (1 == computeItemCount()) {
return 20;
} else if (3 == computeItemCount()) {
return 50;
} else {
return 0;
}
}</programlisting></td>
</tr>
</informaltable>
<para>An experienced programmer claims these two implementations
possibly return different results when executing
<methodname>getScore()</methodname>. Is she right? <emphasis
role="red">Explain</emphasis> your answer.</para>
<tip>
<para>Consider possible side effects of calling
<methodname>computeItemCount()</methodname> and provide an
example.</para>
</tip>
</question>
<answer>
<para>Consider:</para>
<programlisting language="java">public class X {
private static int itemCount = 2;
static int computeItemCount() {return itemCount++;}
...
}</programlisting>
<para>On a fresh start calling
<methodname>computeItemCount()</methodname> for the first time
will return the current value 2 of our variable <code
language="java">itemCount</code>.</para>
<para>The <code language="java">switch</code> implementation will
match its default and thus return 0.</para>
<para>On contrary the <code>if ... else if ... else</code>
implementation will call
<methodname>computeItemCount()</methodname> two times:</para>
<orderedlist>
<listitem>
<para>The first if <code>(1 == computeItemCount())</code>
fails since 1 != 2. This results in incrementing <code
language="java">itemCount</code> by 1 to the new value
3.</para>
</listitem>
<listitem>
<para>Now the else if <code language="java">(3 ==
computeItemCount())</code> clause succeeds. Thus
<methodname>getScore()</methodname> returns 50.</para>
</listitem>
</orderedlist>
<para>So the <code language="java">switch</code> statement
implementing a jump table differs from <code>if ... else if</code>
in definitely calling <code
language="java">computeItemCount()</code> only once.</para>
</answer>
</qandaentry>
</qandadiv>
</qandaset>
</section>
<section xml:id="sd1_exam_2023_summer_task3">
<title>Exception handling</title>
<qandaset defaultlabel="qanda" xml:id="sd1_exam_2023_summer_task2Qanda">
<qandadiv>
<qandaentry>
<question>
<para>Consider the following snippet:</para>
<programlisting language="java">Object o = ...;
int a = ...;
...
try {
String s = (String) o; // May throw a <link
xlink:href="https://freedocs.mi.hdm-stuttgart.de/doc/openjdk-17-doc/api/java.base/java/lang/ClassCastException.html">ClassCastException</link>
int c = 4 / a; // May throw an <link
xlink:href="https://freedocs.mi.hdm-stuttgart.de/doc/openjdk-17-doc/api/java.base/java/lang/ArithmeticException.html">ArithmeticException</link>
} catch (<link xlink:href="https://freedocs.mi.hdm-stuttgart.de/doc/openjdk-17-doc/api/java.base/java/lang/ClassCastException.html">ClassCastException</link> e) {
System.err.println(e.getMessage());
} catch (<link xlink:href="https://freedocs.mi.hdm-stuttgart.de/doc/openjdk-17-doc/api/java.base/java/lang/ArithmeticException.html">ArithmeticException</link> e) {
System.err.println(e.getMessage());
}</programlisting>
<para>Facilitate the above code and <emphasis
role="red">explain</emphasis> why your simpler implementation
always and under all circumstances produces an identical runtime
result.</para>
<tip>
<itemizedlist>
<listitem>
<para>Both <code language="java">catch</code> clauses
contain the same text.</para>
</listitem>
<listitem>
<para>Search the inheritance hierarchy for a common ancestor
class and consider the <methodname>getMessage()</methodname>
method. Where is it actually being defined?</para>
</listitem>
</itemizedlist>
</tip>
</question>
<answer>
<para>Both <link
xlink:href="https://freedocs.mi.hdm-stuttgart.de/doc/openjdk-17-doc/api/java.base/java/lang/ClassCastException.html">ClassCastException</link>
and <link
xlink:href="https://freedocs.mi.hdm-stuttgart.de/doc/openjdk-17-doc/api/java.base/java/lang/ArithmeticException.html">ArithmeticException</link>
are being derived from their common parent <link
xlink:href="https://freedocs.mi.hdm-stuttgart.de/doc/openjdk-17-doc/api/java.base/java/lang/RuntimeException.html">RuntimeException</link>.
All three classes share the common <link
xlink:href="https://freedocs.mi.hdm-stuttgart.de/doc/openjdk-17-doc/api/java.base/java/lang/Throwable.html">Throwable</link>#<link
xlink:href="https://freedocs.mi.hdm-stuttgart.de/doc/openjdk-17-doc/api/java.base/java/lang/Throwable.html#getMessage()">getMessage()</link>
method by inheritance without redefining it.</para>
<para>Our two <code>catch</code> clauses may thus be combined into
one:</para>
<programlisting language="java">...
try {
String s = (String) o; // May throw a <link
xlink:href="https://freedocs.mi.hdm-stuttgart.de/doc/openjdk-17-doc/api/java.base/java/lang/ClassCastException.html">ClassCastException</link>
int c = 4 / a; // May throw an <link
xlink:href="https://freedocs.mi.hdm-stuttgart.de/doc/openjdk-17-doc/api/java.base/java/lang/ArithmeticException.html">ArithmeticException</link>
} catch (<link xlink:href="https://freedocs.mi.hdm-stuttgart.de/doc/openjdk-17-doc/api/java.base/java/lang/RuntimeException.html">RuntimeException</link> e) { // Common parent class
System.err.println(e.getMessage());
}</programlisting>
</answer>
</qandaentry>
</qandadiv>
</qandaset>
</section>
</section>