From a8a175c398fdeae372b8c6ed2e2b784099aa1fee Mon Sep 17 00:00:00 2001
From: Martin Goik <goik@hdm-stuttgart.de>
Date: Wed, 18 Jan 2023 14:23:14 +0100
Subject: [PATCH] Using instanceOf enhancements
---
Doc/Sd1/Collections/collections.xml | 7 +-
Doc/Sd1/CoreClasses/coreClasses.xml | 15 ++---
Doc/Sd1/Inheritance/inheritance.xml | 101 +++++-----------------------
3 files changed, 29 insertions(+), 94 deletions(-)
diff --git a/Doc/Sd1/Collections/collections.xml b/Doc/Sd1/Collections/collections.xml
index 0e607adea..70044ed57 100644
--- a/Doc/Sd1/Collections/collections.xml
+++ b/Doc/Sd1/Collections/collections.xml
@@ -2,6 +2,7 @@
<chapter version="5.1" xml:id="sd1Collection1"
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"
@@ -279,9 +280,9 @@ c12.equals("dummy"):false
@Override
public boolean equals(Object obj) {
- if (obj instanceof Coordinate) {
- return x == ((Coordinate)obj).x &&
- y == ((Coordinate)obj).y;
+ if (obj instanceof Coordinate <emphasis role="red">c</emphasis>) {
+ return x == <emphasis role="red">c</emphasis>.x &&
+ y == <emphasis role="red">c</emphasis>.y;
} else {
return false;
}
diff --git a/Doc/Sd1/CoreClasses/coreClasses.xml b/Doc/Sd1/CoreClasses/coreClasses.xml
index 0aa815184..9ae0e8da4 100644
--- a/Doc/Sd1/CoreClasses/coreClasses.xml
+++ b/Doc/Sd1/CoreClasses/coreClasses.xml
@@ -358,9 +358,9 @@ public boolean equals(Object anObject) {
<programlisting language="java">public class Rectangle {
int width, height;
@Override public boolean equals(Object o) {
- if (o instanceof Rectangle) {
- return width == ((Rectangle) o).width
- && height == ((Rectangle) o).height;
+ if (o instanceof Rectangle <emphasis role="red">r</emphasis>) {
+ return width == <emphasis role="red">r</emphasis>.width
+ && height == <emphasis role="red">r</emphasis>.height;
} else {
return false;
}
@@ -464,11 +464,10 @@ public boolean equals(Object anObject) {
@Override
public boolean equals(final Object o) {
- if (o instanceof TimePeriod) {
- final TimePeriod other = (TimePeriod) o;
- return hours == other.hours &&
- minutes == other.minutes &&
- seconds == other.seconds;
+ if (o instanceof TimePeriod <emphasis role="red">t</emphasis>) {
+ return hours == <emphasis role="red">t</emphasis>.hours &&
+ minutes == <emphasis role="red">t</emphasis>.minutes &&
+ seconds == <emphasis role="red">t</emphasis>.seconds;
} else {
return false;
}
diff --git a/Doc/Sd1/Inheritance/inheritance.xml b/Doc/Sd1/Inheritance/inheritance.xml
index b2067bb3d..8d09d39fc 100644
--- a/Doc/Sd1/Inheritance/inheritance.xml
+++ b/Doc/Sd1/Inheritance/inheritance.xml
@@ -351,12 +351,11 @@ public <link
...
@Override <co linkends="sda_inherit_fig_ShapeEquals-1"
xml:id="sda_inherit_fig_ShapeEquals-1-co"/> public boolean equals(final Object o) {
- if (o instanceof Shape <co linkends="sda_inherit_fig_ShapeEquals-2"
- xml:id="sda_inherit_fig_ShapeEquals-2-co"/>) {
- final Shape other = (Shape) o; <co
- linkends="sda_inherit_fig_ShapeEquals-3"
- xml:id="sda_inherit_fig_ShapeEquals-3-co"/>
- return x == other.x && y == other.y; <co
+ if (o instanceof Shape <emphasis role="red">s</emphasis> <co
+ linkends="sda_inherit_fig_ShapeEquals-2"
+ xml:id="sda_inherit_fig_ShapeEquals-2-co"/>) {
+ return x == <emphasis role="red">s</emphasis>.x && y == <emphasis
+ role="red">s</emphasis>.y; <co
linkends="sda_inherit_fig_ShapeEquals-4"
xml:id="sda_inherit_fig_ShapeEquals-4-co"/>
} else {
@@ -377,12 +376,6 @@ public <link
object?</para>
</callout>
- <callout arearefs="sda_inherit_fig_ShapeEquals-3-co"
- xml:id="sda_inherit_fig_ShapeEquals-3">
- <para>Casting other object to class
- <classname>Shape</classname>.</para>
- </callout>
-
<callout arearefs="sda_inherit_fig_ShapeEquals-4-co"
xml:id="sda_inherit_fig_ShapeEquals-4">
<para>Return <code language="java">true</code> if and only if both
@@ -403,11 +396,11 @@ public <link
<programlisting language="java">public class Rectangle extends Shape {
...
@Override public boolean equals(final Object o) {
- if (o instanceof Rectangle) {
- final Rectangle other = (Rectangle) o;
+ if (o instanceof Rectangle <emphasis role="red">r</emphasis>) {
return super.equals(o) <co linkends="sda_inherit_fig_RectangleEquals-1"
xml:id="sda_inherit_fig_RectangleEquals-1-co"/> &&
- width == other.width && height == other.height <co
+ width == <emphasis role="red">r</emphasis> && height == <emphasis
+ role="red">r</emphasis> <co
linkends="sda_inherit_fig_RectangleEquals-2"
xml:id="sda_inherit_fig_RectangleEquals-2-co"/>;
} else {
@@ -590,7 +583,7 @@ if (day.equals(Day.FRIDAY)) ... // Oops: NPE approaching ...</programlisting>
<title>Overriding toString()</title>
<figure xml:id="sda_inherit_fig_shapeInstanceLog">
- <title> Printing a <classname>Shape</classname>'s info</title>
+ <title>Printing a <classname>Shape</classname>'s info</title>
<informaltable border="0">
<tr>
@@ -1820,12 +1813,13 @@ System.out.print(c.equals(c)); //<emphasis role="red">true</emphasis>: Object
<programlisting language="java">public class Rectangle extends Shape {
@Override public boolean equals(Object o) {
if (o <link
- xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.20.2">instanceof</link> Rectangle) {
+ xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.20.2">instanceof</link> Rectangle <emphasis
+ role="red">r</emphasis>) {
final Rectangle oRectangle = (Rectangle) o; // Cast is «legal»
- return super.equalCenter(oRectangle) &&
- Math.abs(oRectangle.width- width) +
- Math.abs(oRectangle.height- height) < 1.E-15;
+ return super.equalCenter(<emphasis role="red">r</emphasis>) &&
+ Math.abs(<emphasis role="red">r</emphasis>.width- width) +
+ Math.abs(<emphasis role="red">r</emphasis>.height- height) < 1.E-15;
}
return false;
}
@@ -1837,65 +1831,6 @@ System.out.print(c.equals(c)); //<emphasis role="red">true</emphasis>: Object
Rectangle</code> evaluates to <code language="java">false</code>.</para>
</figure>
- <qandaset defaultlabel="qanda" xml:id="sd1_qanda_whyLegalCast">
- <title>Why is <code language="java">oRectangle = (Rectangle) o</code> a
- legal cast?</title>
-
- <qandadiv>
- <qandaentry>
- <question>
- <para>We consider:</para>
-
- <programlisting language="java">Object o = new Scanner(System.in);
-String s = (String) o;</programlisting>
-
- <para>On execution we receive a <classname
- xlink:href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/ClassCastException.html">java.lang.ClassCastException</classname>:</para>
-
- <screen>Exception in thread "main" java.lang.ClassCastException:
- class java.util.Scanner cannot be cast to class java.lang.String
- at q.App.main(App.java:20)</screen>
-
- <para>The comment in <xref
- linkend="sd1_inherit_fig_rectangleEquals"/> states the following
- cast to be legal:</para>
-
- <programlisting language="java">final Rectangle oRectangle = (Rectangle) o; // Cast is «legal»</programlisting>
-
- <para>Why is this claim indeed true?</para>
-
- <para>Don't try digging too deep: The answer is quite
- simple.</para>
- </question>
-
- <answer>
- <para>The cast in question appears within the following <code
- language="java">if</code> block:</para>
-
- <programlisting language="java">if (o <link
- xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.20.2">instanceof</link> Rectangle) {
- final Rectangle oRectangle = (Rectangle) o;
- ...
-}</programlisting>
-
- <para>Thus the cast will only be executed if our variable <code
- language="java">o</code> actually refers to an instance of class
- <classname>Rectangle</classname>. In other words: The <code
- language="java">if</code> block guards our code against illegal
- cast attempts.</para>
-
- <para>Rewriting our faulty code accordingly also removes the
- initial example's runtime exception:</para>
-
- <programlisting language="java">Object o = new Scanner(System.in);
-if (o <link xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.20.2">instanceof</link> String) {
- String s = (String) o; // Unreachable code
-}</programlisting>
- </answer>
- </qandaentry>
- </qandadiv>
- </qandaset>
-
<figure xml:id="sd1_inherit_fig_circleEquals">
<title>Implementing <classname>Circle</classname>.<methodname
xlink:href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#equals(java.lang.Object)">equals()</methodname></title>
@@ -1903,10 +1838,10 @@ if (o <link xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-15
<programlisting language="java">public class Circle extends Shape {
@Override public boolean equals(final Object o) {
if (o <link
- xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.20.2">instanceof</link> Circle){
- final Circle oCircle = (Circle) o;
- return super.equalCenter(o) &&
- Math.abs(oCircle.radius - radius) < 1.E-15;
+ xlink:href="https://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.20.2">instanceof</link> Circle <emphasis
+ role="red">c</emphasis>){
+ return super.equalCenter(<emphasis role="red">c</emphasis>) &&
+ Math.abs(<emphasis role="red">c</emphasis>.radius - radius) < 1.E-15;
}
return false;
} ...</programlisting>
--
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