From 59d1d760bdd3889112a6aba6c2352e7a460f6b6e Mon Sep 17 00:00:00 2001
From: Martin Goik <goik@hdm-stuttgart.de>
Date: Tue, 17 Sep 2019 22:03:24 +0300
Subject: [PATCH] Operator ++, pre/post incremnt, related execises
---
Doc/Sd1/languageFundamentals.xml | 400 ++++++++++++++++++++++++-------
1 file changed, 316 insertions(+), 84 deletions(-)
diff --git a/Doc/Sd1/languageFundamentals.xml b/Doc/Sd1/languageFundamentals.xml
index e88e2f01f..dfc3ad6a3 100644
--- a/Doc/Sd1/languageFundamentals.xml
+++ b/Doc/Sd1/languageFundamentals.xml
@@ -2910,37 +2910,6 @@ System.out.println(intensity);</programlisting>
</qandadiv>
</qandaset>
- <qandaset defaultlabel="qanda" xml:id="sd1_qanda_literalProblem">
- <title>Literal problem</title>
-
- <qandadiv>
- <qandaentry>
- <question>
- <para>Consider:</para>
-
- <programlisting language="java">System.out.println(048);</programlisting>
-
- <para>This yields a compile time error <quote>Integer number too
- large</quote>. On contrary the following code will compile and run
- perfectly well:</para>
-
- <programlisting language="java">System.out.println(047);</programlisting>
-
- <para>Explain the underlying problem.</para>
- </question>
-
- <answer>
- <para>The literal <quote>048</quote> denotes <link
- xlink:href="https://en.wikipedia.org/wiki/Octal">octal
- representation</link>. Digits in octal representation range from 0
- to 7. So <quote>047</quote> is fine but <quote>048</quote> is
- <link linkend="sd1_qanda_illegalOctalLiteral">again</link>
- invalid.</para>
- </answer>
- </qandaentry>
- </qandadiv>
- </qandaset>
-
<qandaset defaultlabel="qanda" xml:id="sd1QandaBinaryIntLiteral">
<title>Binary literals</title>
@@ -3715,6 +3684,187 @@ Expected value: 9223372036854775807</screen>
</imageobject>
</mediaobject>
</figure>
+ </section>
+
+ <section xml:id="sectConversions">
+ <title>Conversions</title>
+
+ <figure xml:id="fig_WideningByte2Short">
+ <title>Widening from <code language="java"
+ xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.2.1-100-A">byte</code>
+ literal to <code language="java"
+ xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.2.1-100-B">short</code></title>
+
+ <mediaobject>
+ <imageobject>
+ <imagedata fileref="Ref/LangFundament/byte2short.svg"/>
+ </imageobject>
+ </mediaobject>
+ </figure>
+
+ <figure xml:id="fig_NarrowingInt2Char">
+ <title>Narrowing from <code language="java"
+ xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.2.1-100-C">int</code>
+ literal to <code language="java"
+ xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.2.1-100-E">char</code>
+ variable</title>
+
+ <mediaobject>
+ <imageobject>
+ <imagedata fileref="Ref/LangFundament/int2char.svg"/>
+ </imageobject>
+ </mediaobject>
+ </figure>
+
+ <figure xml:id="sd1_fig_wideningLadder">
+ <title>A widening «ladder»</title>
+
+ <programlisting language="java">byte byteVariable = 42; // Narrowing: int literal to byte
+short shortVariable = byteVariable; // Widening
+int intVariable = shortVariable; // Widening
+float floatVariable = intVariable; // Widening
+double doubleVariable = floatVariable; // Widening</programlisting>
+ </figure>
+
+ <figure xml:id="sd1_fig_narrowingLadder">
+ <title>A narrowing «ladder»</title>
+
+ <programlisting language="java">double doubleVariable = 14.23;
+float floatVariable = (float) doubleVariable; // Narrowing
+int intVariable = (int) floatVariable; // Narrowing
+short shortVariable = (short) intVariable; // Narrowing
+byte byteVariable = (byte) shortVariable; // Narrowing</programlisting>
+ </figure>
+
+ <qandaset defaultlabel="qanda" xml:id="sd1_qanda_intConverChar">
+ <title><code language="java">int</code> and <code
+ language="java">char</code></title>
+
+ <qandadiv>
+ <qandaentry>
+ <question>
+ <para>Explain the following output:</para>
+
+ <informaltable border="1">
+ <tr>
+ <th>Code</th>
+
+ <th>Output</th>
+ </tr>
+
+ <tr>
+ <td valign="top"><programlisting language="java">char a = 0;
+a -= 1;
+int i = a;
+System.out.println(i);</programlisting></td>
+
+ <td valign="top"><screen>65535</screen></td>
+ </tr>
+ </informaltable>
+
+ <para>Why do we see a result of 65535 rather than -1?</para>
+
+ <tip>
+ <para>Read about the a <code language="java">char</code>'s value
+ range.</para>
+ </tip>
+ </question>
+
+ <answer>
+ <para>In contrast to <code language="java">byte</code>, <code
+ language="java">short</code> and <code language="java">int</code>
+ a two byte <code language="java">char</code> represents no
+ negative but only positive values and zero:</para>
+
+ <informaltable border="1">
+ <tr>
+ <th>decimal</th>
+
+ <th>binary</th>
+ </tr>
+
+ <tr>
+ <td valign="top">0</td>
+
+ <td valign="top"><code language="java">0000 0000 0000
+ 0000</code></td>
+ </tr>
+
+ <tr>
+ <td valign="top">1</td>
+
+ <td valign="top"><code language="java">0000 0000 0000
+ 0001</code></td>
+ </tr>
+
+ <tr>
+ <td valign="top">2</td>
+
+ <td valign="top"><code language="java">0000 0000 0000
+ 0010</code></td>
+ </tr>
+
+ <tr>
+ <td align="center" colspan="2">...</td>
+ </tr>
+
+ <tr>
+ <td valign="top">65535 (<inlineequation>
+ <m:math display="inline">
+ <m:mrow>
+ <m:msup>
+ <m:mi>2</m:mi>
+
+ <m:mi>16</m:mi>
+ </m:msup>
+
+ <m:mo>-</m:mo>
+
+ <m:mi>1</m:mi>
+ </m:mrow>
+ </m:math>
+ </inlineequation>)</td>
+
+ <td valign="top"><code language="java">1111 1111 1111
+ 1111</code></td>
+ </tr>
+ </informaltable>
+
+ <para>Like with other integer types the above table behaves in a
+ cyclic way with respect to additions at its top and and
+ subtractions at its bottom:</para>
+
+ <informaltable border="1">
+ <tr>
+ <th>Code</th>
+
+ <th>Output</th>
+ </tr>
+
+ <tr>
+ <td valign="top"><programlisting language="java">char a = 65535;
+a += 1;
+int i = a;
+System.out.println(i);</programlisting></td>
+
+ <td valign="top"><screen>0</screen></td>
+ </tr>
+ </informaltable>
+
+ <para>On machine level this may be conceived as an (incomplete)
+ subtract operation:</para>
+
+ <programlisting language="none"> 0000 0000 0000 0000
+-0000 0000 0000 0001
+--------------------
+ 1111 1111 1111 1111
+
+
+</programlisting>
+ </answer>
+ </qandaentry>
+ </qandadiv>
+ </qandaset>
<qandaset defaultlabel="qanda" xml:id="sd1_qanda_floatDoubleLiteral">
<title><code>float</code> vs. <code>double</code></title>
@@ -3915,36 +4065,6 @@ System.out.println( 3.14d );</programlisting></td>
</qandaentry>
</qandadiv>
</qandaset>
- </section>
-
- <section xml:id="sectConversions">
- <title>Conversions</title>
-
- <figure xml:id="fig_WideningByte2Short">
- <title>Widening from <code language="java"
- xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.2.1-100-A">byte</code>
- to <code language="java"
- xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.2.1-100-B">short</code></title>
-
- <mediaobject>
- <imageobject>
- <imagedata fileref="Ref/LangFundament/byte2short.svg"/>
- </imageobject>
- </mediaobject>
- </figure>
-
- <figure xml:id="fig_NarrowingInt2Char">
- <title>Narrowing from <code language="java"
- xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.2.1-100-C">int</code>
- to <code language="java"
- xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.2.1-100-E">char</code></title>
-
- <mediaobject>
- <imageobject>
- <imagedata fileref="Ref/LangFundament/int2char.svg"/>
- </imageobject>
- </mediaobject>
- </figure>
<qandaset defaultlabel="qanda" xml:id="qandaNarrowingInt2Char">
<title><code language="java"
@@ -4925,8 +5045,8 @@ New value=-128</screen>
</listitem>
<listitem>
- <para>Moreover the following yields a compile time
- error:</para>
+ <para>Moreover the following logically equivalent code yields
+ a compile time error:</para>
<programlisting language="java">byte a = 127;
System.out.println("value=" + a);
@@ -4986,36 +5106,42 @@ System.out.println("New value=" + a);</programlisting>
<listitem>
<para>The compile time error is due to the definition of the
- <quote>+</quote> operator in Java always returning an <code
- language="java"
+ binary <quote>+</quote> operator: In Java it'll always
+ returning an <code language="java"
xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.2.1-100-C">int</code>
- rather than a byte. Consider:</para>
+ rather than a byte irrespective of it's operands' types.
+ Consider:</para>
<programlisting language="java">byte a = 120, b = 10;
System.out.println(a + b);</programlisting>
- <para>This yields the expected output of 130 and corresponds
- to an <code language="java"
+ <para>This yields the expected output of 130 corresponding to
+ an <code language="java"
xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.2.1-100-C">int</code>
value.</para>
<para>If the expression <code language="java">a + b</code> was
- of data type <code language="java"
+ of type <code language="java"
xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.2.1-100-A">byte</code>
- in <xref linkend="glo_Java"/> an arithmetic overflow as in the
- subsequent code example would occur:</para>
+ an arithmetic overflow as in the subsequent code example would
+ occur:</para>
<programlisting language="java">byte a = 120, b = 10;
-byte sum = (byte) (a + b);
-
-System.out.println(sum);</programlisting>
+byte sum = (byte) (a + b); // yields -126</programlisting>
<para>The explicit type conversion (a so called <quote>type
cast</quote> or cast for short) forces the 4-byte <code
- language="java">int</code> into a one-byte variable <code
- language="java">sum</code> thereby loosing its original value
- and returning -126 instead.</para>
+ language="java">int</code> representing 130 into a one-byte
+ variable <code language="java">sum</code> thereby loosing its
+ original value and assigning -126 instead:</para>
+
+ <screen> 120 00000000 00000000 00000000 01111000
++ 10 + 00000000 00000000 00000000 00001010
+---- -------------------------------------
+ 130 <emphasis role="red">00000000 00000000 00000000</emphasis> 10000010
+
+-126 cast int to byte: -----> 10000010</screen>
<para>Conclusion: <code language="java">a = a + 1</code> and
<code language="java">a++</code> (surprisingly) differ in
@@ -5341,7 +5467,7 @@ System.out.println("Difference: " + difference);</programlisting><screen>Differe
<tr>
<td><code language="java">byte</code></td>
- <td><code language="java">short</code></td>
+ <td><code language="java">byte</code></td>
<td><code language="java">int</code></td>
</tr>
@@ -5373,11 +5499,24 @@ System.out.println("Difference: " + difference);</programlisting><screen>Differe
</figure>
<para xml:id="sd1_explainNoByteByteOperator">The careful reader may
- stumble upon the absence of e.g. a «+» operator turning two byte values
- <code language="java">a</code> and <code language="java">b</code> into an
- expression <code language="java">a + b</code> of type <code
- language="java">byte</code> rather than <code language="java">int</code>.
- This is due to a Java Virtual Machine <link
+ stumble upon the absence of e.g. a binary «+» operator turning two byte
+ values <code language="java">a</code> and <code language="java">b</code>
+ into an expression <code language="java">a + b</code> of type <code
+ language="java">byte</code> rather than <code
+ language="java">int</code>:</para>
+
+ <figure xml:id="sd1_fig_noBinaryPlusByteByte">
+ <title>No binary + operator yielding <code
+ language="java">byte</code></title>
+
+ <programlisting language="java">byte a = 1, b = 2;
+
+<emphasis role="red">byte sum = a + b; // Error: Incompatible types.
+ // Required: byte
+ // Found: int</emphasis></programlisting>
+ </figure>
+
+ <para>This is due to a Java Virtual Machine <link
xlink:href="https://docs.oracle.com/javase/specs/jvms/se10/html/jvms-2.html#jvms-2.11.1-120">design
decision</link> leading to a <link
xlink:href="https://docs.oracle.com/javase/specs/jvms/se10/html/jvms-2.html#jvms-2.11.1-320">limited
@@ -6144,11 +6283,104 @@ char resultChar= s + c; // Incompatible types Required: char found: int</prog
</qandadiv>
</qandaset>
+ <figure xml:id="sd1_fig_OperatorPlusPlus">
+ <title>Unary <code language="java">++</code> operator</title>
+
+ <para>Increment variable by 1:</para>
+
+ <informaltable border="0">
+ <tr>
+ <td valign="top"><programlisting language="none">int a = 4;
+System.out.println("Before:" + a);
+<emphasis role="red">a = a + 1</emphasis>;
+System.out.println("After:" + a);</programlisting></td>
+
+ <td valign="top"><programlisting language="none">int a = 4;
+System.out.println("Before:" + a);
+<emphasis role="red">a++</emphasis>;
+System.out.println("After:" + a);</programlisting></td>
+ </tr>
+
+ <tr>
+ <th colspan="2"><screen>Before:4
+After:5</screen></th>
+ </tr>
+ </informaltable>
+ </figure>
+
+ <figure xml:id="sd1_fig_OperatorPlusPlusPostfixPrefix">
+ <title>Prefix and postfix notation</title>
+
+ <informaltable border="1">
+ <colgroup width="7%"/>
+
+ <colgroup width="44%"/>
+
+ <colgroup width="7%"/>
+
+ <colgroup width="42%"/>
+
+ <tr>
+ <th colspan="2">pre-increment</th>
+
+ <th colspan="2">post-increment</th>
+ </tr>
+
+ <tr>
+ <td colspan="2" valign="top"><programlisting language="none">int a = 4;
+int b = <emphasis role="red">++a</emphasis>;
+System.out.println(b);</programlisting></td>
+
+ <td colspan="2" valign="top"><programlisting language="none">int a = 4;
+int b = <emphasis role="red">a++</emphasis>;
+System.out.println(b);</programlisting></td>
+ </tr>
+
+ <tr>
+ <td>Output: </td>
+
+ <td valign="top"><screen>5</screen></td>
+
+ <td>Output:</td>
+
+ <td valign="top"><screen>4</screen></td>
+ </tr>
+ </informaltable>
+ </figure>
+
+ <qandaset defaultlabel="qanda" xml:id="sd1_qanda_threeQaysExpression">
+ <title>Three ways expressing the same</title>
+
+ <qandadiv>
+ <qandaentry>
+ <question>
+ <para>Write the expression <code language="java">a = a - 1</code>
+ in two alternate ways.</para>
+
+ <tip>
+ <para>Use two different operators.</para>
+ </tip>
+ </question>
+
+ <answer>
+ <itemizedlist>
+ <listitem>
+ <para><code language="java">a -= 1</code></para>
+ </listitem>
+
+ <listitem>
+ <para><code language="java">a--</code></para>
+ </listitem>
+ </itemizedlist>
+ </answer>
+ </qandaentry>
+ </qandadiv>
+ </qandaset>
+
<figure xml:id="sd1_fig_OperatorExamples">
<title>Operator examples</title>
<programlisting language="java">//Integer
-i++; i = i + 1; // Increment by one
i--; i = i - 1; // Decrement by one
i += b; i = i + b; // Raise by b's value
i %= 3; i = i % 3; // Modulus of 3
--
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