statements.xml

<?xml version="1.0" encoding="UTF-8"?>
<chapter annotations="slide" version="5.1" xml:id="sd1_chap_Statements"
         xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xmlns:xila="http://www.w3.org/2001/XInclude/local-attributes"
         xmlns:xi="http://www.w3.org/2001/XInclude"
         xmlns:svg="http://www.w3.org/2000/svg"
         xmlns:ns="http://docbook.org/ns/transclusion"
         xmlns:m="http://www.w3.org/1998/Math/MathML"
         xmlns:html="http://www.w3.org/1999/xhtml"
         xmlns:db="http://docbook.org/ns/docbook">
  <title>Statements</title>

  <info>
    <abstract>
      <para>Purposes of statements:</para>

      <para>Declaring variables and assigning values.</para>

      <para>Control <emphasis role="bold">whether</emphasis> code will be
      executed.</para>

      <para>Control <emphasis role="bold">how often</emphasis> code will be
      executed.</para>
    </abstract>
  </info>

  <figure xml:id="sd1_fig_StatementEndSemicolon">
    <title>Statements: General syntax</title>

    <para>Statement's body terminated by <quote>;</quote></para>

    <programlisting language="none">{statement};</programlisting>
  </figure>

  <figure xml:id="sd1_fig_StatementDeclareVariable">
    <title>Statement examples: Declaring and assigning variables</title>

    <glosslist>
      <glossentry>
        <glossterm>Variable declaration:</glossterm>

        <glossdef>
          <programlisting language="java">int a;</programlisting>
        </glossdef>
      </glossentry>

      <glossentry>
        <glossterm>Value assignment:</glossterm>

        <glossdef>
          <programlisting language="java">a = 33;</programlisting>
        </glossdef>
      </glossentry>

      <glossentry>
        <glossterm>Combined declaration and assignment:</glossterm>

        <glossdef>
          <programlisting language="java">int a = 33;</programlisting>
        </glossdef>
      </glossentry>
    </glosslist>
  </figure>

  <figure xml:id="sd1_fig_StatementVsExpression">
    <title>Expression <abbrev>vs.</abbrev> statement</title>

    <glosslist>
      <glossentry>
        <glossterm>Expression:</glossterm>

        <glossdef>
          <programlisting language="java">a - 4</programlisting>
        </glossdef>
      </glossentry>

      <glossentry>
        <glossterm>Statement:</glossterm>

        <glossdef>
          <programlisting language="java">b = a - 4;</programlisting>

          <para>Notice the trailing <quote><code>;</code></quote>.</para>
        </glossdef>
      </glossentry>
    </glosslist>
  </figure>

  <figure xml:id="sd1_fig_MultiStmtPerLine">
    <title>Multiple statements per line</title>

    <programlisting language="java">a = b + 3; b = a - 4;</programlisting>

    <para>Discouraged by good coding practices:</para>

    <itemizedlist>
      <listitem>
        <para>Poor readability</para>
      </listitem>

      <listitem>
        <para>Hampers debugging</para>
      </listitem>
    </itemizedlist>
  </figure>

  <figure xml:id="sd1_fig_DebugMultiStmtPerLine">
    <title>Debugging multiple statements per line</title>

    <mediaobject>
      <imageobject>
        <imagedata fileref="Fig/multipleStatementPerLine.svg"/>
      </imageobject>
    </mediaobject>
  </figure>

  <figure xml:id="sd1_fig_Blocks">
    <title>Blocks</title>

    <programlisting language="java">double initialAmount = 34;
{ <emphasis role="red">// first block</emphasis>
  final double interestRate = 1.2; // 1.2%
  System.out.println("Interest:" + initialAmount * interestRate / 100);
}
{ <emphasis role="red">// second block</emphasis>
  final double interestRate = 0.8; // 0.8%
  System.out.println("Interest:" + initialAmount * interestRate / 100);
}</programlisting>

    <informaltable border="1">
      <tr>
        <td><itemizedlist>
            <listitem>
              <para>Defining scopes</para>
            </listitem>

            <listitem>
              <para>Unit of work</para>
            </listitem>
          </itemizedlist></td>

        <td><itemizedlist>
            <listitem>
              <para><code language="java">if</code>: Conditional block
              execution.</para>
            </listitem>

            <listitem>
              <para><code language="java">for</code> / <code
              language="java">while</code>: Repeated block execution.</para>
            </listitem>
          </itemizedlist></td>
      </tr>
    </informaltable>
  </figure>

  <section xml:id="sd1_sect_statements_if">
    <title>The if conditional statement</title>

    <figure xml:id="sd1_fig_if">
      <title>Conditional block execution</title>

      <informaltable border="1">
        <tr>
          <td valign="top"><programlisting language="java">double saving = 320.00;

if (1000 &lt;= saving) {
  // Rich customer, 1,2% interest rate
  System.out.println(
    "Interest:" + 1.2 * saving / 100);
}
System.out.println("Done!");</programlisting></td>

          <td rowspan="2" valign="top"><mediaobject>
              <imageobject>
                <imagedata fileref="Fig/if.svg"/>
              </imageobject>
            </mediaobject></td>
        </tr>

        <tr>
          <td><screen>Done!</screen></td>
        </tr>
      </informaltable>
    </figure>

    <figure xml:id="sd1_fig_ifSyntax">
      <title><code language="java">if</code> syntax</title>

      <programlisting language="java">if (booleanExpression)
  (block | statement)</programlisting>
    </figure>

    <section xml:id="sd1_sect_else">
      <title>if-then-<code>else</code></title>

      <figure xml:id="sd1_fig_ifElse">
        <title><code language="java">if</code> ... <code
        language="java">else</code></title>

        <informaltable border="1">
          <tr>
            <td valign="top"><programlisting language="java">double saving = 320.00;

if (1000 &lt;= saving <co linkends="sd1_fig_ifElse-1"
                  xml:id="sd1_fig_ifElse-1-co"/>)  { <co
                  linkends="sd1_fig_ifElse-2" xml:id="sd1_fig_ifElse-2-co"/>
  // Rich customer, 1,2% interest rate
  System.out.println(
     "Interest:" + 1.2 * saving / 100);
} <co linkends="sd1_fig_ifElse-3" xml:id="sd1_fig_ifElse-3-co"/> else { <co
                  linkends="sd1_fig_ifElse-4" xml:id="sd1_fig_ifElse-4-co"/>
  // Joe customer, 0.8%
  // standard interest rate
  System.out.println(
    "Interest:" + 0.8 * saving / 100);
}
System.out.println("Done!");</programlisting><screen>Interest:2.56
Done!</screen></td>

            <td valign="top"><mediaobject>
                <imageobject>
                  <imagedata fileref="Fig/ifElse.svg"/>
                </imageobject>
              </mediaobject></td>
          </tr>
        </informaltable>

        <calloutlist role="slideExclude">
          <callout arearefs="sd1_fig_ifElse-1-co" xml:id="sd1_fig_ifElse-1">
            <para>Decision on boolean expression.</para>
          </callout>

          <callout arearefs="sd1_fig_ifElse-2-co" xml:id="sd1_fig_ifElse-2">
            <para>Conditional execution of on block or single
            statement.</para>
          </callout>

          <callout arearefs="sd1_fig_ifElse-3-co" xml:id="sd1_fig_ifElse-3">
            <para>Required branch being executed in case of boolean expression
            being true.</para>
          </callout>

          <callout arearefs="sd1_fig_ifElse-4-co" xml:id="sd1_fig_ifElse-4">
            <para>Optional branch corresponding to boolean expression being
            false.</para>
          </callout>
        </calloutlist>
      </figure>

      <figure xml:id="sd1_fig_ifElseSyntax">
        <title><code language="java">if ... else</code> syntax</title>

        <programlisting language="java">if (booleanExpression)
   (block | statement)
[else
   (block | statement) ] <co linkends="sd1_fig_ifElseSyntax-1"
            xml:id="sd1_fig_ifElseSyntax-1-co"/></programlisting>

        <calloutlist role="slideExclude">
          <callout arearefs="sd1_fig_ifElseSyntax-1-co"
                   xml:id="sd1_fig_ifElseSyntax-1">
            <para>The <quote>[...]</quote> pair of braces denotes an optional
            clause that may or may not be present.</para>

            <para>Thus only the first part <quote><code language="java">if
            (booleanExpression) (block | statement)</code></quote> is
            mandatory.</para>
          </callout>
        </calloutlist>
      </figure>

      <figure xml:id="sd1_fig_bestPracticeCompareEquals">
        <title>Best practices comparing for equality</title>

        <para>Use</para>

        <programlisting language="java">if (4 == variable) ...</programlisting>

        <para>in favour of:</para>

        <programlisting language="java">if (variable == 4) ... <co
            linkends="sd1_fig_bestPracticeCompareEquals-1"
            xml:id="sd1_fig_bestPracticeCompareEquals-1-co"/></programlisting>

        <calloutlist role="slideExclude">
          <callout arearefs="sd1_fig_bestPracticeCompareEquals-1-co"
                   xml:id="sd1_fig_bestPracticeCompareEquals-1">
            <para>Some programming languages allow for interpreting integer
            values as logical expressions. In »C / C++« for example an
            <code>int</code> value of zero is equivalent to <code>false</code>
            and nonzero values evaluate to <code>true</code>. Consider the
            following snippet:</para>

            <programlisting language="c">if (variable = 4) {...} /* Just a single "=" rather then "==" */</programlisting>

            <para>A <xref linkend="glo_Java"/> compiler will flag this as a
            compile time error. On contrary in »C / C++« this is perfectly
            correct code: The term <code>variable = 4</code> having a nonzero
            value of 4 evaluates to <code>true</code> which in real code would
            most likely be a bug. Subject to choosing compiler warning options
            the possible damage may be mitigated depending on the observer's
            degree of pedantry.</para>

            <para>Changing the order however even in »C / C++« results in a
            compile time error since we cannot assign a value to a
            literal:</para>

            <programlisting language="java">if (4 = variable) {...} // Compile time error, even in C/C++</programlisting>

            <para>We are thus able to avoid this type of error in the first
            place.</para>
          </callout>
        </calloutlist>
      </figure>

      <qandaset defaultlabel="qanda" xml:id="sd1_qanda_betterSimpleMath">
        <title>Providing better display</title>

        <qandadiv>
          <qandaentry>
            <question>
              <para>We reconsider <xref
              linkend="sd1_qanda_simpleMath"/>:</para>

              <informaltable border="1">
                <tr>
                  <th>Source code</th>

                  <th>Output</th>
                </tr>

                <tr>
                  <td valign="top"><programlisting language="java">int a = -4,
    b = 100;

System.out.println(a + "+" + b+ "=" + (a + b));</programlisting></td>

                  <td valign="top"><screen>-4+100=96</screen></td>
                </tr>
              </informaltable>

              <para>Unfortunately a negative value yields:</para>

              <informaltable border="1">
                <tr>
                  <th>Source code</th>

                  <th>Output</th>
                </tr>

                <tr>
                  <td valign="top"><programlisting language="java">int a = 100,
    b = -4;

System.out.println(a + "+" + b + "=" + (a + b));</programlisting></td>

                  <td valign="top"><screen>100+-4=96</screen></td>
                </tr>
              </informaltable>

              <para>This result looks awkward. Modify the code to see
              <code>100-4=96</code> in such cases. You may reconsider the
              findings from <xref linkend="sd1QandaBracesInPrintln"/>.</para>
            </question>

            <answer>
              <para>The following simple solution does not work:</para>

              <informaltable border="0">
                <tr>
                  <th>Source code</th>

                  <th>Output</th>
                </tr>

                <tr>
                  <td valign="top"><programlisting language="java">int a = 100,
    b = -4;

if (b &lt; 0) {
    System.out.println(a + b + "=" + (a + b));
  } else {
    System.out.println(a + "+" + b + "=" + (a + b));
}</programlisting></td>

                  <td valign="top"><screen>96=96</screen></td>
                </tr>
              </informaltable>

              <para>Since <code language="java">a</code> and <code
              language="java">b</code> are both variables of type <code
              language="java">int</code> they get added rather than string
              style concatenated:</para>

              <programlisting language="none">System.out.println(a + b + "=" + (a + b));
                    <emphasis role="red">╲  ╱    ╱      ╲ ╱ 
                     96    ╱        96
                       ╲  ╱        ╱ 
                       "96="      ╱ 
                          ╲      ╱ 
                           "96=96"</emphasis></programlisting>

              <para>Resolving this issue may be effected by adding an empty
              string <coref
              linkend="sd1_qanda_betterSimpleMathEmptyString-1-co"/> forcing
              <xref linkend="glo_Java"/> to use the concatenation
              <quote>+</quote> operator in favour of the arithmetic
              one:</para>

              <programlisting language="none">System.out.println(a + ""<co
                  xml:id="sd1_qanda_betterSimpleMathEmptyString-1-co"/> + b + "=" + (a + b));
                    <emphasis role="red">╲ ╱       ╱            ╲ ╱ 
                   "100"     ╱             96
                      ╲     ╱             ╱ 
                       "100-4"           ╱ 
                             ╲          ╱ 
                              "100-4=96"</emphasis></programlisting>

              <informaltable border="0">
                <tr>
                  <th>Source code</th>

                  <th>Output</th>
                </tr>

                <tr>
                  <td valign="top"><programlisting language="java">int a = 100,
    b = -4;

if (b &lt; 0) {
    System.out.println(a + ""  + b + "=" + (a + b));
  } else {
    System.out.println(a + "+" + b + "=" + (a + b));
}</programlisting></td>

                  <td valign="top"><screen>100-4=96</screen></td>
                </tr>
              </informaltable>
            </answer>
          </qandaentry>
        </qandadiv>
      </qandaset>

      <qandaset defaultlabel="qanda" xml:id="sd1_qanda_booleanEqual">
        <title>Comparing for equality</title>

        <qandadiv>
          <qandaentry>
            <question>
              <para>Copy the following snippet into your <xref
              linkend="glo_IDE"/>:</para>

              <programlisting language="java">int count = 1;

if (count = 4) { // is count equal to 4?
  System.out.println("count is o.K.");
}</programlisting>

              <para>The <xref linkend="glo_Java"/> compiler will indicate an
              error:</para>

              <screen>Incompatible types.
Required: <emphasis role="red">boolean</emphasis>
Found: <emphasis role="red">int</emphasis></screen>

              <para>Explain its cause in detail by examining the <code
              language="java">count = 4</code> expression.</para>

              <tip>
                <para><xref linkend="glo_Java"/> provides two similar looking
                operators <code language="java">=</code> and <code
                language="java">==</code> having (totally) different
                semantics.</para>
              </tip>
            </question>

            <answer>
              <para>The two operators <code language="java">=</code> and <code
              language="java">==</code> are <emphasis>completely</emphasis>
              unrelated:</para>

              <glosslist>
                <glossentry>
                  <glossterm><code language="java">=</code></glossterm>

                  <glossdef>
                    <para>This is being called the assignment operator. A
                    typical statement reads <code language="java">a =
                    34</code> assigning the <code language="java">int</code>
                    value <code language="java">34</code> to a variable <code
                    language="java">a</code>.</para>

                    <para>Note this operator's semantics being completely
                    different from even elementary math syntax.
                    Consider:</para>

                    <informalequation>
                      <m:math display="block">
                        <m:mrow>
                          <m:mi>x</m:mi>

                          <m:mo>=</m:mo>

                          <m:mi>y</m:mi>
                        </m:mrow>

                        <m:mo>⇒</m:mo>

                        <m:mrow>
                          <m:msup>
                            <m:mi>x</m:mi>

                            <m:mi>2</m:mi>
                          </m:msup>

                          <m:mo>=</m:mo>

                          <m:msup>
                            <m:mi>y</m:mi>

                            <m:mi>2</m:mi>
                          </m:msup>
                        </m:mrow>
                      </m:math>
                    </informalequation>

                    <para>In math <quote>=</quote> denotes the equality of
                    objects <abbrev>e.g.</abbrev> values, sets, functions and
                    so on.</para>
                  </glossdef>
                </glossentry>

                <glossentry>
                  <glossterm><code language="java">==</code></glossterm>

                  <glossdef>
                    <para>The comparison operator matching the usual math
                    semantics comparing:</para>

                    <itemizedlist>
                      <listitem>
                        <para><xref linkend="glo_Java"/> primitive types for
                        equality of value.</para>
                      </listitem>

                      <listitem>
                        <para><xref linkend="glo_Java"/> objects for
                        identity.</para>
                      </listitem>
                    </itemizedlist>

                    <para>In particular an expression like <code
                    language="java">count == 4</code> is of type boolean being
                    either <code language="java">true</code> or <code
                    language="java">false</code>.</para>
                  </glossdef>
                </glossentry>
              </glosslist>

              <para>More formally the expression <code language="java">count =
              4</code> is of type <code language="java">int</code> evaluating
              to 4 (surprise!). However an <code language="java">if
              (...)</code> operates on <code language="java">boolean</code>
              values only and <code language="java">if (4)</code> thus does
              not make sense at all. The code in question may therefore be
              re-written as:</para>

              <programlisting language="java">int count = 1;

int countAssignment = (count = 4); // Assigning expression count = 4 to variable countAssignment.

if (countAssignment) { <emphasis role="red">// Error: An int is not a boolean!</emphasis>
  System.out.println("count is o.K.");
}</programlisting>

              <para>Since the assignment operator is being evaluated from
              right to left we actually do not need braces:</para>

              <programlisting language="java">...
int countAssignment = count = 4; // Assigning expression count = 4 to variable countAssignment
...</programlisting>

              <para>This code is equivalent to its counterpart with respect to
              compilation. The comment <quote>is count equal to 4?</quote> is
              thus misleading: The intended comparison requires using the
              <quote>==</quote> operator rather than an assignment operator
              <quote>=</quote>. Changing it the resulting expression is indeed
              of type <code language="java">boolean</code>:</para>

              <programlisting language="java">int count = 4 + 3;
final boolean test = (count == 4); // Now using "==" (comparison) in favour of "=" (assignment)
System.out.println("test=" + test);</programlisting>

              <para>Again we may omit braces here due to operator priority
              rules:</para>

              <programlisting language="java">...
final boolean test = count == 4; // Now using "==" (comparison) in favour of "=" (assignment)
...</programlisting>

              <para>The <code language="java">boolean</code> variable <code
              language="java">test</code> will receive a value of <code
              language="java">false</code> as expected. Thus our initial code
              just needs a tiny modification replacing the assignment operator
              «<code language="java">=</code>» by the comparison operator
              «<code language="java">==</code>»:</para>

              <programlisting language="java">int count = 1;

if (count == 4) { // is count equal to 4?
  System.out.println("count is o.K.");
}</programlisting>

              <note xml:id="sd1_note_useLiteralEqualsVariable">
                <para>In contrast to <xref linkend="glo_Java"/> some
                programming languages like C and C++ allow for integer values
                in <code language="java">if (...)</code> conditionals:</para>

                <programlisting language="c">#include &lt;stdio.h&gt;

int main(int argc, char **args) {

  int a = 3;
  if (a = 4) {
     printf("a has got a value of 4\n");
  }
}</programlisting>

                <para>The integer expression <code language="java">count =
                4</code> has got a value of 4. Integer values inside an <code
                language="java">if (...)</code> statement will be evaluated
                as:</para>

                <glosslist>
                  <glossentry>
                    <glossterm>true</glossterm>

                    <glossdef>
                      <para>if the expression's value differs from zero</para>
                    </glossdef>
                  </glossentry>

                  <glossentry>
                    <glossterm>false</glossterm>

                    <glossdef>
                      <para>if the expression's value equals zero</para>
                    </glossdef>
                  </glossentry>
                </glosslist>

                <para>Thus in C and C++ the expression <code
                language="java">if(count = 4)</code> will always evaluate to
                <code language="java">true</code> irrespective of the variable
                <code language="java">count</code>'s initial value. Most
                important: The C compiler will not issue an error or warning
                unless non-default, more restrictive compile time warning
                options are being activated. Consider this widely used
                «feature» to be dangerous at best.</para>

                <para>For this reason it is good practice always using <code
                language="java">if (4 == count)</code> rather than <code
                language="java">if (count == 4)</code>: Even in C you cannot
                assign a value to a constant literal. Thus an accidentally
                mistyped <code language="java">if (4 = count)</code> statement
                will definitively result in a compile time error most likely
                saving its author from tedious debugging.</para>
              </note>
            </answer>
          </qandaentry>
        </qandadiv>
      </qandaset>

      <figure xml:id="sd1_fig_IfOmitBlocks">
        <title>Single statement branches</title>

        <para>Branches containing exactly one statement don't require a block
        definition.</para>

        <programlisting language="java">double initialAmount = 3200;

if (100000 &lt;= initialAmount)
  System.out.println("Interest:" + 1.2 * initialAmount / 100);
else if (1000 &lt;= initialAmount)
  System.out.println("Interest:" + 0.8 * initialAmount / 100);
else
  System.out.println("Interest:" + 0);</programlisting>
      </figure>

      <figure xml:id="sd1_fig_ifElseNested">
        <title>Nested <code language="java">if ... else</code></title>

        <informaltable border="1">
          <col width="40%"/>

          <col width="60%"/>

          <tr>
            <td valign="top"><programlisting language="java">if ('A' == grade || 'B' == grade) {
   result = "Excellent";
} else {
   if ('C' == grade) {
      result = "O.k.";
   } else {
      if ('D' == grade) {
         result = "Passed";
      } else {
         result = "Failed";
      }
   }
}</programlisting></td>

            <td valign="top"><mediaobject>
                <imageobject>
                  <imagedata fileref="Fig/if_elseIf_else.svg"/>
                </imageobject>
              </mediaobject></td>
          </tr>
        </informaltable>
      </figure>
    </section>

    <section xml:id="sd1_sect_elseif">
      <title>Using <code language="java">else if</code></title>

      <figure xml:id="sd1_fig_ifElse_else">
        <title>Enhanced readability: <code language="java">if ... else if ...
        else</code></title>

        <informaltable border="1">
          <col width="40%"/>

          <col width="60%"/>

          <tr>
            <td valign="top"><programlisting language="java">if ('A' == grade || 'B' == grade) {
   result = "Excellent";
} else if ('C' == grade) {
   result = "O.k.";
} else if ('D' == grade) {
   result = "Passed";
} else {
   result = "Failed";
}</programlisting></td>

            <td valign="top"><mediaobject>
                <imageobject>
                  <imagedata fileref="Fig/if_elseIf_else.svg"/>
                </imageobject>
              </mediaobject></td>
          </tr>
        </informaltable>
      </figure>

      <figure xml:id="sd1_fig_ifElse_elseSyntax">
        <title><code language="java">if ... else if ... else</code>
        syntax</title>

        <programlisting language="java">if (booleanExpression)
   (block | statement)
[else if (booleanExpression)
   (block | statement) ]* <co linkends="sd1_fig_ifElse_elseSyntax-1"
            xml:id="sd1_fig_ifElse_elseSyntax-1-co"/>
[else
  (block | statement) ] <co linkends="sd1_fig_ifElse_elseSyntax-2"
            xml:id="sd1_fig_ifElse_elseSyntax-2-co"/></programlisting>

        <calloutlist role="slideExclude">
          <callout arearefs="sd1_fig_ifElse_elseSyntax-1-co"
                   xml:id="sd1_fig_ifElse_elseSyntax-1">
            <para>The pair of braces [...] indicates an optional clause. The
            asterisk <quote>*</quote> indicates an arbitrary number of
            repetitions (zero to infinity).</para>
          </callout>

          <callout arearefs="sd1_fig_ifElse_elseSyntax-2-co"
                   xml:id="sd1_fig_ifElse_elseSyntax-2">
            <para>The second pair of braces [...] again indicates an optional
            clause.</para>

            <para>Thus only the <quote><code language="java">if
            (booleanExpression) (block | statement)</code></quote> clause is
            mandatory.</para>
          </callout>
        </calloutlist>
      </figure>

      <qandaset defaultlabel="qanda" xml:id="sd1_qanda_replaceElseIf">
        <title>Replacing <code language="java">else if (...){...}</code> by
        nested <code language="java">if ... else</code> statements</title>

        <qandadiv>
          <qandaentry>
            <question>
              <para>A computer newbie did not yet read about the <code
              language="java">else if(...)</code> branch construct but
              nevertheless tries to implement the following logic:</para>

              <programlisting language="java">if (a &lt; 7) {
  System.out.println("o.K.");
} else if (5 == b) {
  System.out.println("Maybe");
} else {
  System.out.println("Wrong!");
}</programlisting>

              <para><code language="java">a</code> and <code
              language="java">b</code> are supposed to be <code
              language="java">int</code> variables. Please help our newbie
              using just <code language="java">if(...){...} else {...} </code>
              avoiding <code language="java"><emphasis role="red">else
              if</emphasis>(...) {}</code> branch statements!</para>

              <tip>
                <para>As the title suggests you may want to nest an
                <quote>inner</quote> <code language="java">if(...)</code>
                inside an <quote>outer</quote> one.</para>
              </tip>
            </question>

            <answer>
              <para>The solution requires replacing the <code
              language="java">else if(...)</code> branch by a nested <code
              language="java">if(...){ ...} else {...}</code> statement by
              moving the final <code language="java">else</code> block into
              the nested one.</para>

              <programlisting language="java">if (a &lt; 7) {
    System.out.println("o.K.");
} else {
    if (5 == b) {
        System.out.println("Maybe");
    } else {
        System.out.println("Wrong!");
    }
}</programlisting>
            </answer>
          </qandaentry>
        </qandadiv>
      </qandaset>

      <figure xml:id="sd1_fig_useScannerClass">
        <title>User input recipe</title>

        <informaltable border="0">
          <col width="64%"/>

          <col width="36%"/>

          <tr>
            <td valign="top"><programlisting language="java">import java.util.Scanner;

public class App {
  public static void main(String[] args){

    final Scanner scan = 
        new Scanner(System.in);
    System.out.print("Enter a value:");
    final int value = scan.nextInt();
    System.out.println("You entered "
       + value);
  }
}</programlisting></td>

            <td valign="top"><screen>Enter a value:123
You entered 123</screen><para>See <methodname
            xlink:href="javaapi://java.util.Scanner#nextBoolean()">nextBoolean()</methodname>,
            <methodname><link
            xlink:href="javaapi://java.util.Scanner#nextByte()">nextByte()</link></methodname>
            and friends.</para></td>
          </tr>
        </informaltable>
      </figure>

      <qandaset defaultlabel="qanda" xml:id="sw1QandaPostExamBonuspoints">
        <title>Post modifying an exam's marking</title>

        <qandadiv>
          <qandaentry>
            <question>
              <para>A lecturer marks an exam having a maximum of 12 reachable
              points:</para>

              <informaltable border="1" width="25%">
                <tr>
                  <th>Name</th>

                  <th>Mark</th>
                </tr>

                <tr>
                  <td>Aaron</td>

                  <td>3</td>
                </tr>

                <tr>
                  <td>Maureen</td>

                  <td>11</td>
                </tr>

                <tr>
                  <td>Sally</td>

                  <td>1</td>
                </tr>

                <tr>
                  <td>...</td>

                  <td>...</td>
                </tr>
              </informaltable>

              <para>The lecturer is dissatisfied with the overall result. He
              wants to add 3 bonus points but still keeping the maximum of 12
              points to be reachable:</para>

              <informaltable border="1" width="25%">
                <tr>
                  <th>Name</th>

                  <th>Mark</th>

                  <th>3 bonus points augmented mark</th>
                </tr>

                <tr>
                  <td>Aaron</td>

                  <td>3</td>

                  <td>6</td>
                </tr>

                <tr>
                  <td>Maureen</td>

                  <td>11</td>

                  <td><emphasis role="red">12</emphasis></td>
                </tr>

                <tr>
                  <td>Sally</td>

                  <td>1</td>

                  <td>4</td>
                </tr>

                <tr>
                  <td>...</td>

                  <td>...</td>

                  <td>...</td>
                </tr>
              </informaltable>

              <para>Complete the following code by assigning this modified
              number of points to the variable <code
              language="java">newResult</code>.</para>

              <programlisting language="java">public static void main(String[] args) {

  int pointsReached = 7;         // May range from 0 to 12 points
  final int maximumPoints = 12;
  final int pointsToAdd = 3;

  final int augmentedMark;

  // TODO: Assignment to variable augmentedMark

  System.out.println("New Result:" + augmentedMark);
}</programlisting>
            </question>

            <answer>
              <para>We present three different solutions:</para>

              <orderedlist>
                <listitem>
                  <para>The basic task is to add up the values of <code
                  language="java">pointsReached</code> and <code
                  language="java">pointsToAdd</code>. This sum however must
                  not exceed the <code language="java">maximumPoints</code>
                  limit. We use an <code language="java">if</code> statement
                  for constraint safeguarding:</para>

                  <programlisting language="java">public static void main(String[] args) {

  final int pointsReached = 7;
  final int maximumPoints = 12;
  final int pointsToAdd = 3;

  final int augmentedMark;