From 9294cbc2cd91dfaa01235e62833277cd24cdd1e1 Mon Sep 17 00:00:00 2001
From: "Dr. Martin Goik" <goik@hdm-stuttgart.de>
Date: Fri, 12 Jul 2019 21:33:45 +0200
Subject: [PATCH] int to Double auto boxing exercise
---
Doc/Sd1/workingWithNumbers.xml | 163 ++++++++++++++++++++-------------
1 file changed, 100 insertions(+), 63 deletions(-)
diff --git a/Doc/Sd1/workingWithNumbers.xml b/Doc/Sd1/workingWithNumbers.xml
index d19fb504c..212a13934 100644
--- a/Doc/Sd1/workingWithNumbers.xml
+++ b/Doc/Sd1/workingWithNumbers.xml
@@ -139,69 +139,69 @@ int iPrimitiveFromInteger = <co linkends="sd1_numbers_fig_conventional-3"
</tr>
</informaltable>
- <informaltable role="slideExclude" border="1">
- <colgroup width="50%"/>
-
- <colgroup width="50%"/>
-
- <tr>
- <th>Boxing and unboxing</th>
-
- <th><quote>Conventional</quote> <xref linkend="glo_Java"/></th>
- </tr>
-
- <tr>
- <td valign="top"><calloutlist>
- <callout arearefs="sd1_numbers_fig_boxingAndUnboxing-1-co"
- xml:id="sd1_numbers_fig_boxingAndUnboxing-1">
- <para>Defining a primitive <code language="java">int</code>
- value.</para>
- </callout>
-
- <callout arearefs="sd1_numbers_fig_boxingAndUnboxing-2-co"
- xml:id="sd1_numbers_fig_boxingAndUnboxing-2">
- <para>Creating an instance of <classname
- xlink:href="https://docs.oracle.com/javase/10/docs/api/java/lang/Integer.html">Integer</classname>
- by means of boxing.</para>
- </callout>
-
- <callout arearefs="sd1_numbers_fig_boxingAndUnboxing-3-co"
- xml:id="sd1_numbers_fig_boxingAndUnboxing-3">
- <para>Assigning an <classname
- xlink:href="https://docs.oracle.com/javase/10/docs/api/java/lang/Integer.html">Integer</classname>'s
- value to a primitive <code language="java">int</code> by means
- of unboxing.</para>
- </callout>
- </calloutlist></td>
-
- <td valign="top"><calloutlist>
- <callout arearefs="sd1_numbers_fig_conventional-1-co"
- xml:id="sd1_numbers_fig_conventional-1">
- <para>Defining a primitive <code language="java">int</code>
- value.</para>
- </callout>
-
- <callout arearefs="sd1_numbers_fig_conventional-2-co"
- xml:id="sd1_numbers_fig_conventional-2">
- <para>Creating a new instance of <classname
- xlink:href="https://docs.oracle.com/javase/10/docs/api/java/lang/Integer.html">Integer</classname>
- using the class method <methodname
- xlink:href="https://docs.oracle.com/javase/10/docs/api/java/lang/Integer.html#valueOf-int-">Integer
- valueOf​(int i)</methodname>.</para>
- </callout>
-
- <callout arearefs="sd1_numbers_fig_conventional-3-co"
- xml:id="sd1_numbers_fig_conventional-3">
- <para>Assigning an <classname
- xlink:href="https://docs.oracle.com/javase/10/docs/api/java/lang/Integer.html">Integer</classname>'s
- value to a primitive <code language="java">int</code> using the
- <methodname
- xlink:href="https://docs.oracle.com/javase/10/docs/api/java/lang/Integer.html#intValue--">int
- intValue()</methodname> instance method.</para>
- </callout>
- </calloutlist></td>
- </tr>
- </informaltable>
+ <informaltable border="1" role="slideExclude">
+ <colgroup width="50%"/>
+
+ <colgroup width="50%"/>
+
+ <tr>
+ <th>Boxing and unboxing</th>
+
+ <th><quote>Conventional</quote> <xref linkend="glo_Java"/></th>
+ </tr>
+
+ <tr>
+ <td valign="top"><calloutlist>
+ <callout arearefs="sd1_numbers_fig_boxingAndUnboxing-1-co"
+ xml:id="sd1_numbers_fig_boxingAndUnboxing-1">
+ <para>Defining a primitive <code language="java">int</code>
+ value.</para>
+ </callout>
+
+ <callout arearefs="sd1_numbers_fig_boxingAndUnboxing-2-co"
+ xml:id="sd1_numbers_fig_boxingAndUnboxing-2">
+ <para>Creating an instance of <classname
+ xlink:href="https://docs.oracle.com/javase/10/docs/api/java/lang/Integer.html">Integer</classname>
+ by means of boxing.</para>
+ </callout>
+
+ <callout arearefs="sd1_numbers_fig_boxingAndUnboxing-3-co"
+ xml:id="sd1_numbers_fig_boxingAndUnboxing-3">
+ <para>Assigning an <classname
+ xlink:href="https://docs.oracle.com/javase/10/docs/api/java/lang/Integer.html">Integer</classname>'s
+ value to a primitive <code language="java">int</code> by means
+ of unboxing.</para>
+ </callout>
+ </calloutlist></td>
+
+ <td valign="top"><calloutlist>
+ <callout arearefs="sd1_numbers_fig_conventional-1-co"
+ xml:id="sd1_numbers_fig_conventional-1">
+ <para>Defining a primitive <code language="java">int</code>
+ value.</para>
+ </callout>
+
+ <callout arearefs="sd1_numbers_fig_conventional-2-co"
+ xml:id="sd1_numbers_fig_conventional-2">
+ <para>Creating a new instance of <classname
+ xlink:href="https://docs.oracle.com/javase/10/docs/api/java/lang/Integer.html">Integer</classname>
+ using the class method <methodname
+ xlink:href="https://docs.oracle.com/javase/10/docs/api/java/lang/Integer.html#valueOf-int-">Integer
+ valueOf​(int i)</methodname>.</para>
+ </callout>
+
+ <callout arearefs="sd1_numbers_fig_conventional-3-co"
+ xml:id="sd1_numbers_fig_conventional-3">
+ <para>Assigning an <classname
+ xlink:href="https://docs.oracle.com/javase/10/docs/api/java/lang/Integer.html">Integer</classname>'s
+ value to a primitive <code language="java">int</code> using
+ the <methodname
+ xlink:href="https://docs.oracle.com/javase/10/docs/api/java/lang/Integer.html#intValue--">int
+ intValue()</methodname> instance method.</para>
+ </callout>
+ </calloutlist></td>
+ </tr>
+ </informaltable>
</figure>
<figure xml:id="sd1_numbers_fig_stackBoxUnboxVsConventional">
@@ -238,6 +238,43 @@ while (!values.empty()) {
</tr>
</informaltable>
</figure>
+
+ <qandaset defaultlabel="qanda"
+ xml:id="sd1_numbers_qanda_boxing_int2Double">
+ <title>Auto boxing int to Double?</title>
+
+ <qandadiv>
+ <qandaentry>
+ <question>
+ <para>Consider the following boxing conversion:</para>
+
+ <programlisting language="java">double d = 3.0;
+Double dInstance = d;</programlisting>
+
+ <para>This code compiles and executes perfectly well. On contrary
+ the following snippet does not:</para>
+
+ <programlisting language="java">int i = 3;
+Double dInstance = i;</programlisting>
+
+ <para>Explain this result. Hint: You may want to read <link
+ xlink:href="https://docs.oracle.com/javase/specs/jls/se12/html/jls-5.html">chapter
+ 5</link> and <link
+ xlink:href="https://docs.oracle.com/javase/specs/jls/se12/html/jls-5.html#jls-5.2">section
+ 5.2</link> in particular from the <link
+ xlink:href="https://docs.oracle.com/javase/specs/jls/se12/html/">The
+ Java® Language Specification</link>.</para>
+ </question>
+
+ <answer>
+ <para>The compiler will not perform auto boxing from
+ <code>int</code> do <code>Double</code>. On the other hand Double
+ is no subtype of Integer disallowing a widening reference
+ conversion.</para>
+ </answer>
+ </qandaentry>
+ </qandadiv>
+ </qandaset>
</section>
<section xml:id="sd1_numbers_sect_numberParsing">
--
GitLab