diff --git a/Doc/Sd1/objectsClasses.xml b/Doc/Sd1/objectsClasses.xml
index 2b6860ed0dc76f04617869d92ffe23cf1534e051..e70dfb4a9e046fa572c099f6179e3d5beaacfc14 100644
--- a/Doc/Sd1/objectsClasses.xml
+++ b/Doc/Sd1/objectsClasses.xml
@@ -4221,58 +4221,72 @@ public class Circle {
<para>This is a follow-up exercise to <xref
linkend="sd1_qanda_seconds2weeks"/> implementing a corresponding
<classname>Timeperiod</classname> class. Consider the subsequent
- example demonstrating both its intended use constructor and
- <methodname>toString()</methodname> method:</para>
+ example:</para>
<informaltable border="0">
<tr>
<td valign="top"><programlisting language="java">final long seconds = 112223;
-final Timeperiod t = new Timeperiod(112223);
-System.out.println(seconds + " seconds are equal to " + t);</programlisting></td>
+final Timeperiod tPeriod = new Timeperiod(112223); <co
+ linkends="sd1_qanda_seconds2weeks_Class-1"
+ xml:id="sd1_qanda_seconds2weeks_Class-1-co"/>
+System.out.println(seconds + " seconds are equal to " + tPeriod <co
+ linkends="sd1_qanda_seconds2weeks_Class-2"
+ xml:id="sd1_qanda_seconds2weeks_Class-2-co"/>); </programlisting><calloutlist>
+ <callout arearefs="sd1_qanda_seconds2weeks_Class-1-co"
+ xml:id="sd1_qanda_seconds2weeks_Class-1">
+ <para>This requires a constructor definition
+ <methodname>Timeperiod(long)</methodname>.</para>
+ </callout>
+
+ <callout arearefs="sd1_qanda_seconds2weeks_Class-2-co"
+ xml:id="sd1_qanda_seconds2weeks_Class-2">
+ <para>This requires a
+ <methodname>toString()</methodname> method within your
+ <classname>Timeperiod</classname> class matching
+ <classname
+ xlink:href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Object.html">Object</classname>.<methodname
+ xlink:href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Object.html#toString()">toString()</methodname>'s
+ method signature.</para>
+ </callout>
+ </calloutlist></td>
<td valign="top"><screen>1 day, 7 hours, 10 minutes and 23 seconds</screen></td>
</tr>
</informaltable>
<para>Since the <methodname>toString()</methodname> method may
- not be called at all it shall be implemented on demand in
- analogy to <xref linkend="sd1_qanda_defineStringClass"/>. Tip:
- create a suitable attribute being <code
- language="java">null</code> initially. If
+ not be called at all it shall be implemented in a »on demand«
+ fashion similar to <xref
+ linkend="sd1_qanda_defineStringClass"/>. Hint: create a suitable
+ attribute being <code language="java">null</code> initially. If
<methodname>toString()</methodname> is being called, first check
- for <code language="java">null</code> and initialize it on
- demand only.</para>
+ for <code language="java">null</code> and initialize it by the
+ desired output if so required.</para>
<para>Furthermore individual weeks, days, hours, minutes and
- seconds shall be implemented as read-only values using <code
- language="java">final</code>:</para>
+ seconds shall be implemented as read-only values:</para>
<informaltable border="0">
<tr>
- <td valign="top"><programlisting language="java">final Timeperiod t = new Timeperiod(2310983);
-System.out.print("weeks = " + t.weeks +
- "\ndays = " + t.days +
- "\nhours = " + t.hours +
- "\nminutes = " + t.minutes +
- "\nseconds = " + t.seconds);</programlisting></td>
-
- <td valign="top"><screen>weeks = 3
-days = 5
-hours = 17
-minutes = 56
-seconds = 23</screen></td>
+ <td valign="top"><programlisting language="java">final Timeperiod tPeriod = new Timeperiod(2310983);
+System.out.print("weeks = " + tPeriod.weeks);
+
+tPeriod.days = 5; // Expected compile time error:
+ // Cannot assign a value to final variable 'days'</programlisting></td>
+
+ <td valign="top"><screen>weeks = 3</screen></td>
</tr>
</informaltable>
- <para>In other words: The <classname>Timeperiod</classname>
- class should be implemented as an <link
- xlink:href="https://docs.oracle.com/javase/tutorial/essential/concurrency/immutable.html">immutable</link>.
- Thus once a <classname>Timeperiod</classname> instance has been
- created it shall be impossible to alter the instance's values
- <abbrev>i.e.</abbrev> changing its state.</para>
+ <para>In other words: Instances of
+ <classname>Timeperiod</classname> should be <link
+ xlink:href="https://docs.oracle.com/javase/tutorial/essential/concurrency/immutable.html">immutable</link>
+ objects. Once a <classname>Timeperiod</classname> instance has
+ been created it shall be impossible to alter its internal
+ state.</para>
- <para>Supply a so called copy constructor to allow for creating
- a new instance from an existing one:</para>
+ <para>In addition supply a so called copy constructor to allow
+ for creating a new instance from an existing one:</para>
<programlisting language="java">/**
* Clone a given instance.
@@ -4281,8 +4295,8 @@ seconds = 23</screen></td>
*/
public Timeperiod(final Timeperiod timeperiod) { ... }</programlisting>
- <para>Use the following tests to check your
- implementation:</para>
+ <para>Use the following unit tests to check your
+ implementation's correctness:</para>
<programlisting language="java">public class TimeperiodTest {
@@ -4318,10 +4332,14 @@ public Timeperiod(final Timeperiod timeperiod) { ... }</programlisting>
expectedSeconds, expectedMinutes, expectedHours, expectedDays, expectedWeeks, expectedToString,
period);
- // Also testing copy constructor
+ // Testing copy constructor
+ final Timeperiod periodClone = new Timeperiod(period);
+
+ Assert.assertTrue("A cloned instance must differ from its original", periodClone != period);
+
assertPeriodEqualImplement(
expectedSeconds, expectedMinutes, expectedHours, expectedDays, expectedWeeks, expectedToString,
- new Timeperiod(period));
+ periodClone);
}
/**
@@ -4380,18 +4398,20 @@ public Timeperiod(final Timeperiod timeperiod) { ... }</programlisting>
<answer>
<para>Our implementation basically reads:</para>
- <programlisting language="java">public <link
- xlink:href="https://gitlab.mi.hdm-stuttgart.de/goik/GoikLectures/blob/master/P/Sd1/Timeperiod/src/main/java/de/hdm_stuttgart/mi/sd1/Timeperiod.java">Timeperiod</link>(final Timeperiod timeperiod) {
+ <programlisting language="java">public class <link
+ xlink:href="https://gitlab.mi.hdm-stuttgart.de/goik/GoikLectures/blob/master/P/Sd1/Timeperiod/src/main/java/de/hdm_stuttgart/mi/sd1/Timeperiod.java">Timeperiod</link> {
- public final int seconds, minutes, hours, days, weeks;
- // Constructors and toString() ...
+ // Constructors, toString() and other methods
+ // ...
+ public final int seconds, minutes, hours, days, weeks; // Instance state
}</programlisting>
<para>The <code language="java">final</code> modifier ensures
- instances to be immutable requiring all values to be set within
- any constructor. We thus decompose the desired number of seconds
- into weeks, days, hours, minutes and remaining seconds:</para>
+ instances being immutable thus requiring all values to be set
+ within any constructor being defined. We thus decompose the
+ desired number of seconds into weeks, days, hours, minutes and
+ remaining seconds:</para>
<programlisting language="java">public <link
xlink:href="https://gitlab.mi.hdm-stuttgart.de/goik/GoikLectures/blob/master/P/Sd1/Timeperiod/src/main/java/de/hdm_stuttgart/mi/sd1/Timeperiod.java#L65">Timeperiod</link>(int seconds) {
@@ -4409,11 +4429,85 @@ public Timeperiod(final Timeperiod timeperiod) { ... }</programlisting>
this.seconds = seconds % SECONDS_PER_MINUTE; // remaining seconds
}</programlisting>
- <para>Notice the <code language="java">this.seconds</code>
- qualification being required to disambiguate the constructor
- parameter variable <code language="java">Timeperiod(int
- seconds)</code> from the instance member variable <code
- language="java">Timeperiod.seconds</code>.</para>
+ <para>Notice the <code>this.<emphasis
+ role="red">seconds</emphasis></code> qualification being
+ required to disambiguate the constructor parameter variable
+ <code>Timeperiod(int <emphasis
+ role="red">seconds</emphasis>)</code> scope from the instance
+ member variable scope <code>Timeperiod.<emphasis
+ role="red">seconds</emphasis></code>.</para>
+
+ <para>The toString() method could be defined
+ straightforwardly:</para>
+
+ <programlisting language="java">public String toString() {
+ final int largestNonZeroComponent;
+
+ if (0 < weeks) {
+ largestNonZeroComponent = 5; // weeks, days, hours, minutes and seconds
+ } else if (0 < days) {
+ largestNonZeroComponent = 4; // days, hours, minutes and seconds
+ } else if (0 < hours) {
+ largestNonZeroComponent = 3; // hours, minutes and seconds
+ } else if (0 < minutes) {
+ largestNonZeroComponent = 2; // minutes and seconds
+ } else {
+ largestNonZeroComponent = 1; // only seconds, potentially zero as well
+ }
+
+ final StringBuffer buffer = new StringBuffer();
+ switch (largestNonZeroComponent) {
+ case 5: addSingularOrPlural(buffer, weeks, "week", ", ");
+ case 4: addSingularOrPlural(buffer, days, "day", ", ");
+ case 3: addSingularOrPlural(buffer, hours, "hour", ", ");
+ case 2: addSingularOrPlural(buffer, minutes, "minute", ", ");
+ case 1: addSingularOrPlural(buffer, seconds, "second", " and ");
+ }
+ return buffer.toString();
+}</programlisting>
+
+ <para>This solution provides the desired result. However if
+ being called repeatedly it causes a performance penalty. We thus
+ refine it by a lazy initialization mechanism. In the first step
+ we simply rename our method having just <code
+ language="java">private</code> one:</para>
+
+ <programlisting language="java">private String toStringImplement() {
+ final int largestNonZeroComponent;
+
+ if (0 < weeks) {
+ largestNonZeroComponent = 5;
+ ...
+
+ return buffer.toString();
+}</programlisting>
+
+ <para>We now re-implement our desired
+ <methodname>toString()</methodname> method in a lazy
+ initialisation fashion by introducing an additional
+ <code>private</code> attribute:</para>
+
+ <programlisting language="java">public class Timeperiod {
+
+ // Tedious calculation, will only be initialized on-demand
+ private String toStringValue = null;
+
+ ...
+
+ public String toString() {
+ // Calculation is tedious, thus performing it only on-demand.
+ //
+ if (null == toStringValue) { // Called for the first time, not yet initialized?
+ toStringValue = toStringImplement();
+ }
+ return toStringValue;
+ }
+}</programlisting>
+
+ <para>See <link
+ xlink:href="https://gitlab.mi.hdm-stuttgart.de/goik/GoikLectures/blob/master/P/Sd1/Timeperiod/src/main/java/de/hdm_stuttgart/mi/sd1/Timeperiod.java">Timeperiod</link>
+ for a complete solution including a copy constructor
+ implementation.</para>
</answer>
</qandaentry>
</qandadiv>
diff --git a/P/Sd1/Timeperiod/src/main/java/de/hdm_stuttgart/mi/sd1/Timeperiod.java b/P/Sd1/Timeperiod/src/main/java/de/hdm_stuttgart/mi/sd1/Timeperiod.java
index 9d9a1337ae05bab1f907cf35c05fe7283ee7245d..6afdb8aa45f4116ced7cd56e1adedda1ac3fcd09 100644
--- a/P/Sd1/Timeperiod/src/main/java/de/hdm_stuttgart/mi/sd1/Timeperiod.java
+++ b/P/Sd1/Timeperiod/src/main/java/de/hdm_stuttgart/mi/sd1/Timeperiod.java
@@ -7,33 +7,33 @@ package de.hdm_stuttgart.mi.sd1;
*/
public class Timeperiod {
- // Pre-caculated internal values
+ // Pre-calculated internal values
static private final int
SECONDS_PER_MINUTE = 60, // 60 minutes per hour
SECONDS_PER_HOUR = 60 * SECONDS_PER_MINUTE, // 3600 seconds per hour
SECONDS_PER_DAY = 24 * SECONDS_PER_HOUR, // 86400 seconds per day
SECONDS_PER_WEEK = 7 * SECONDS_PER_DAY; // 604800 seconds per week
- // Tedious calculation, will happen only on-demand
+ // Tedious calculation, will only be initialized on-demand
private String toStringValue = null;
private String toStringImplement() {
- final int highestValue;
+ final int largestNonZeroComponent;
if (0 < weeks) {
- highestValue = 5; // weeks, days, hours, minutes and seconds
+ largestNonZeroComponent = 5; // weeks, days, hours, minutes and seconds
} else if (0 < days) {
- highestValue = 4; // days, hours, minutes and seconds
+ largestNonZeroComponent = 4; // days, hours, minutes and seconds
} else if (0 < hours) {
- highestValue = 3; // hours, minutes and seconds
+ largestNonZeroComponent = 3; // hours, minutes and seconds
} else if (0 < minutes) {
- highestValue = 2; // minutes and seconds
+ largestNonZeroComponent = 2; // minutes and seconds
} else {
- highestValue = 1; // only seconds, potentially zero as well
+ largestNonZeroComponent = 1; // only seconds, potentially zero as well
}
final StringBuffer buffer = new StringBuffer();
- switch (highestValue) {
+ switch (largestNonZeroComponent) {
case 5: addSingularOrPlural(buffer, weeks, "week", ", ");
case 4: addSingularOrPlural(buffer, days, "day", ", ");
case 3: addSingularOrPlural(buffer, hours, "hour", ", ");
@@ -102,9 +102,9 @@ public class Timeperiod {
*/
@Override
public String toString() {
- // Value calculation is tedious, thus doing it only on-demand.
+ // Calculation is tedious, thus performing it only on-demand.
//
- if (null == toStringValue) { // Called for the first time, yet uninitialized?
+ if (null == toStringValue) { // Called for the first time, not yet initialized?
toStringValue = toStringImplement();
}
return toStringValue;
diff --git a/P/Sd1/Timeperiod/src/test/java/de/hdm_stuttgart/mi/sd1/TimeperiodTest.java b/P/Sd1/Timeperiod/src/test/java/de/hdm_stuttgart/mi/sd1/TimeperiodTest.java
index 9eafe78a61f78e9e3c2434192b43f169bbc38d44..e8641184489eb73081f227e51f482e691c5a883e 100644
--- a/P/Sd1/Timeperiod/src/test/java/de/hdm_stuttgart/mi/sd1/TimeperiodTest.java
+++ b/P/Sd1/Timeperiod/src/test/java/de/hdm_stuttgart/mi/sd1/TimeperiodTest.java
@@ -40,10 +40,14 @@ public class TimeperiodTest {
expectedSeconds, expectedMinutes, expectedHours, expectedDays, expectedWeeks, expectedToString,
period);
- // Also testing copy constructor
+ // Testing copy constructor
+ final Timeperiod periodClone = new Timeperiod(period);
+
+ Assert.assertTrue("A cloned instance must differ from its original", periodClone != period);
+
assertPeriodEqualImplement(
expectedSeconds, expectedMinutes, expectedHours, expectedDays, expectedWeeks, expectedToString,
- new Timeperiod(period));
+ periodClone);
}
/**