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pearcej merged 3 commits into from
Aug 6, 2026
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Issue 370 parson, 3.1 and 3,2 #371

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3b4875d
added parson related to section 3.1
habibasorour Aug 6, 2026
a01cde6
added for 3.2
habibasorour Aug 6, 2026
0f25a90
fixed spacing
habibasorour Aug 6, 2026
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153 changes: 122 additions & 31 deletions source/ch3_javadatatypes.ptx
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Original file line number Diff line number Diff line change
Expand Up @@ -281,42 +281,75 @@ public class TempConv {
The general rule in Java is that you must decide what kind of an object your variable is going to reference and then you must declare that variable before you use it. In our temperature converter, the calculation <c>(fahr - 32) * 5.0/9.0</c> works correctly because 5.0 and 9.0 are treated as double values, preventing the integer division that would occur if we had written <c>5/9</c>, which would result in 0.
</p>


<exercise xml:id="java-square-number-exercise" label="java-square-number-exercise">
<exercise xml:id="java-km-to-miles-parsons-exercise" label="java-km-to-miles-parsons">
<statement>
<p>
Write a program that converts km to miles. Use the <c>Scanner</c> class to read the input. Note that 1 km is approximately equal to 0.621 miles.
Construct a complete Java program that reads a distance in kilometers from the user and converts it to miles.
Drag the blocks into the correct order on the right.
</p>
<program xml:id="java-square-number" interactive="activecode" language="java">
<input>
public class KmToMiles {
public static void main(String[] args) {
// write your code here
}
}
</input> <stdin> </stdin>
</program>
</statement>
<solution>
<program language="java">
<input>
import java.util.Scanner;
public class KmToMiles {
public static void main(String[] args) {
Double kilometers;
Double miles;
Scanner input;
input = new Scanner(System.in);
System.out.print("Enter distance in kilometers: ");
kilometers = input.nextDouble();
miles = kilometers * 0.621;
System.out.println(kilometers + " kilometers is equal to " + miles + " miles.");
}
}
</input>
</program>
</solution>

<blocks>
<block order="1">
<choice correct="yes">
<cline>import java.util.Scanner;</cline>
</choice>
<choice correct="no">
<cline>import Scanner;</cline>
</choice>
</block>

<block order="2">
<cline>public class KmToMiles {</cline>
</block>

<block order="3">
<cline> public static void main(String[] args) {</cline>
</block>

<block order="4">
<cline>Scanner input;</cline>
<cline>Double kilometers;</cline>
<cline>Double miles;</cline>
</block>

<block order="5">
<choice correct="yes">
<cline> input = new Scanner(System.in);</cline>
</choice>
<choice correct="no">
<cline> input = new Scanner(System.out);</cline>
</choice>
</block>

<block order="6">
<choice correct="yes">
<cline> kilometers = input.nextDouble();</cline>
</choice>
<choice correct="no">
<cline> kilometers = input.readDouble();</cline>
</choice>
</block>

<block order="7">
<choice correct="yes">
<cline> miles = kilometers * 0.621;</cline>
</choice>
<choice correct="no">
<cline> miles = kilometers / 0.621;</cline>
</choice>
</block>

<block order="8">
<cline> System.out.println(kilometers + " kilometers is equal to " + miles + " miles.");</cline>
</block>
<block order="9">
<cline> }</cline>
<cline>}</cline>
</block>
</blocks>
</exercise>


</subsection>
</section>
Expand Down Expand Up @@ -485,6 +518,63 @@ void main() {
<p>
In <xref ref="downcasting-example" text="type-global"/>, we first create a <c>Dog</c> object and assign it to an <c>Animal</c> reference (upcasting). Then, we check if the <c>Animal</c> reference is actually pointing to a <c>Dog</c> object before downcasting it back to a <c>Dog</c> reference.
</p>

<exercise xml:id="java-downcasting-parsons-exercise" label="java-downcasting-parsons">
<statement>
<p>
Construct a program that safely downcasts a <c>Shape</c> reference to a <c>Circle</c> object and calls a subclass method.
Drag the blocks into the correct order on the right.
</p>
</statement>
<blocks>
<block order="1">
<cline>class Shape {
...
}</cline>
</block>

<block order="2">
<cline>class Circle extends Shape {</cline>
<cline>public void drawCircle() {
System.out.println("Circle");
}</cline>
<cline>}</cline>
</block>

<block order="3">
<cline>public class Downcast {</cline>
<cline> public static void main(String[] args) {</cline>
<cline> Shape myShape = new Circle();</cline>
</block>

<block order="4">
<choice correct="yes">
<cline> if (myShape instanceof Circle) {</cline>
</choice>
<choice correct="no">
<cline> if (myShape.equals(Circle)) {</cline>
</choice>
</block>

<block order="5">
<choice correct="yes">
<cline> Circle myCircle = (Circle) myShape;</cline>
<cline> myCircle.drawCircle();</cline>
</choice>
<choice correct="no">
<cline> Circle myCircle = myShape;</cline>
<cline> myCircle.drawCircle();</cline>
</choice>
</block>

<block order="6">
<cline> }</cline>
<cline> }</cline>
<cline>}</cline>
</block>
</blocks>
</exercise>

</section>


Expand Down Expand Up @@ -1171,6 +1261,7 @@ public class HistoMap {
</choice>
</choices>
</exercise>

</reading-questions>
</section>
</chapter>