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‎source/ch4_conditionals.ptx‎

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<chapter xml:id="conditionals">
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<title>Conditionals</title>
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<section xml:id="simple-if">
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<title>Using the Simple <c>if</c> Statement</title>
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<section xml:id="using-conditional-in-java"> <title>Using Conditional Statements in Java</title>
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<p><idx>conditional statements</idx>
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Conditional statements in Python and Java are very similar.
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In Python we have three patterns:
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Once again you can see that in Java the curly braces define a block rather than indentation.
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In Java, the parentheses around the condition are required because it is technically a function that evaluates to <c>True</c> or <c>False</c>.
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</p>
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</section>
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<section xml:id="use-the-if-else-statement">
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<subsection xml:id="use-the-if-else-statement">
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<title>Using the <c>if</c> - <c>else</c> Statement</title>
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<p><xref ref= "python-if-else" text="type-global"/> shows how the <c>if</c> - <c>else</c>statement is written in Python.</p>
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</code>
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</program>
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</listing>
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</section>
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</subsection>
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<section xml:id="elif">
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<subsection xml:id="elif">
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<title>Can we use <c>elif</c>?</title>
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<p><idx><c>elif</c> statement</idx>
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</code> <tests> </tests>
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</program>
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</listing>
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</section>
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</subsection>
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<section xml:id="switch">
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<subsection xml:id="switch">
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<title>Using the <c>switch</c> Statement</title>
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<p>
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</p>
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<p>
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Finally, the <c>switch</c> statement does not support relational expressions such as greater than or less than. So you cannot use it to completely replace the <c>elif</c>. Even with the new features of Java 14+ the <c>switch</c> statement is still limited to constant comparisons using equality.</p>
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</subsection>
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</section>
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<section xml:id="exception-handling">
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<section xml:id="ternary-operator">
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<title>The Ternary Operator</title>
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<p><idx>Boolean operators</idx> <idx>simple comparisons</idx> <idx>compound Boolean expressions</idx>
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The conditionals used in the if statement can be <term>Boolean variables</term>, <term>simple comparisons</term>, and <term>compound Boolean expressions</term>.
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</p>
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<p><idx>ternary operator</idx>
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Java also provides the ternary operator <c>condition ? valueIfTrue : valueIfFalse</c>, which lets you use a <c>boolean</c> test directly inside an assignment. If the condition is true, the first value is chosen; otherwise, the second value is used. <xref ref="ternary-operator-table" text="type-global"/> summarizes how it works.
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</p>
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<table xml:id="ternary-operator-table">
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<title>Ternary Operator in Java</title>
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<tabular>
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<row>
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<cell><term>Component</term></cell>
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<cell><term>Description</term></cell>
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</row>
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<row>
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<cell><c>condition</c></cell>
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<cell>The <c>boolean</c> expression that is evaluated (e.g., <c>a % 2 == 0</c>).</cell>
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</row>
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<row>
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<cell><c>?</c></cell>
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<cell> This is the ternary operator that separates the condition from the <c>trueValue</c>.</cell>
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</row>
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<row>
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<cell><c>trueValue</c></cell>
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<cell>The value assigned if the condition is true (e.g., <c>a * a</c>).</cell>
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</row>
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<row>
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<cell><c>:</c></cell>
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<cell> This is the ternary operator that separates the <c>trueValue</c> from the <c>falseValue</c>.</cell>
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</row>
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<row>
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<cell><c>falseValue</c></cell>
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<cell>The value assigned if the condition is false (e.g., <c>3 * x - 1</c>).</cell>
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</row>
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<row>
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<cell>Example Usage</cell>
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<cell><c>a = a % 2 == 0 ? a * a : 3 * x - 1</c></cell>
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</row>
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<row>
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<cell>Equivalent if-else Code</cell>
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<cell>Can also be written with a regular <c>if-else</c> statement, but the ternary form is more concise.</cell>
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</row>
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</tabular>
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</table>
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<p>
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Using this operator can make code shorter and more readable in cases where a simple conditional assignment is needed. <xref ref="java-ternary" text="type-global"/> shows an example where we see the same logic implemented in two different ways.
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</p>
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<listing xml:id="java-ternary">
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<program interactive="activecode" language ="java">
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<code>
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public class Ternary {
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public static void main(String[] args) {
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int a = 4;
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int x = 2;
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int outp;
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// ternary:
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outp = (a % 2 == 0) ? (a * a) : (3 * x - 1);
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System.out.println("ternary result: " + outp);
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// Equivalent using if/else
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if (a % 2 == 0) {
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outp = a * a;
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} else {
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outp = 3 * x - 1;
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}
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System.out.println("if/else result: " + outp);
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}
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}
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</code>
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</program>
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</listing>
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<p>
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In <xref ref="java-ternary" text="type-global"/>, we are using this ternary operator to assign a value to <c>a</c> based on whether <c>a</c> is even or odd. If <c>a</c> is even, it will be squared; if odd, it will be instead be calculated as <c>3 * x - 1</c>. This is a concise way to write conditional assignments in Java. However, you might want to use it sparingly, as it can make code less readable if overused or used with complex expressions.
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</p>
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</section>
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<section xml:id="exception-handling">
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<title>Exception Handling</title>
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<p>
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Note that as with other structures in Java, <c>try-catch</c> blocks blocks must be encased with braces <c>{}</c>. The most important part of this code is, after <c>catch</c>, there is a set of parenthesis with an exception type and a variable name <c>catch (InputMismatchException e)</c>. This is where we declare a <c>InputMismatchException</c> exception and name it with the variable name <c>e</c>. It is common practice, though not a requirement, to name exception variables <c>e</c> in this manner.
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</p>
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</section>
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<section xml:id="ternary-operator">
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<title>The Ternary Operator</title>
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<p><idx>Boolean operators</idx> <idx>simple comparisons</idx> <idx>compound Boolean expressions</idx>
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The conditionals used in the if statement can be <term>Boolean variables</term>, <term>simple comparisons</term>, and <term>compound Boolean expressions</term>.
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</p>
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<p><idx>ternary operator</idx>
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Java also provides the ternary operator <c>condition ? valueIfTrue : valueIfFalse</c>, which lets you use a <c>boolean</c> test directly inside an assignment. If the condition is true, the first value is chosen; otherwise, the second value is used. <xref ref="ternary-operator-table" text="type-global"/> summarizes how it works.
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</p>
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<table xml:id="ternary-operator-table">
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<title>Ternary Operator in Java</title>
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<tabular>
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<row>
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<cell><term>Component</term></cell>
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<cell><term>Description</term></cell>
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</row>
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<row>
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<cell><c>condition</c></cell>
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<cell>The <c>boolean</c> expression that is evaluated (e.g., <c>a % 2 == 0</c>).</cell>
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</row>
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<row>
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<cell><c>?</c></cell>
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<cell> This is the ternary operator that separates the condition from the <c>trueValue</c>.</cell>
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</row>
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<row>
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<cell><c>trueValue</c></cell>
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<cell>The value assigned if the condition is true (e.g., <c>a * a</c>).</cell>
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</row>
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<row>
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<cell><c>:</c></cell>
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<cell> This is the ternary operator that separates the <c>trueValue</c> from the <c>falseValue</c>.</cell>
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</row>
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<row>
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<cell><c>falseValue</c></cell>
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<cell>The value assigned if the condition is false (e.g., <c>3 * x - 1</c>).</cell>
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</row>
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<row>
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<cell>Example Usage</cell>
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<cell><c>a = a % 2 == 0 ? a * a : 3 * x - 1</c></cell>
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</row>
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<row>
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<cell>Equivalent if-else Code</cell>
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<cell>Can also be written with a regular <c>if-else</c> statement, but the ternary form is more concise.</cell>
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</row>
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</tabular>
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</table>
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<p>
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Using this operator can make code shorter and more readable in cases where a simple conditional assignment is needed. <xref ref="java-ternary" text="type-global"/> shows an example where we see the same logic implemented in two different ways.
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</p>
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<listing xml:id="java-ternary">
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<program interactive="activecode" language ="java">
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<code>
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public class Ternary {
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public static void main(String[] args) {
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int a = 4;
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int x = 2;
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int outp;
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// ternary:
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outp = (a % 2 == 0) ? (a * a) : (3 * x - 1);
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System.out.println("ternary result: " + outp);
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// Equivalent using if/else
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if (a % 2 == 0) {
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outp = a * a;
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} else {
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outp = 3 * x - 1;
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}
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System.out.println("if/else result: " + outp);
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}
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}
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</code>
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</program>
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</listing>
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<p>
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In <xref ref="java-ternary" text="type-global"/>, we are using this ternary operator to assign a value to <c>a</c> based on whether <c>a</c> is even or odd. If <c>a</c> is even, it will be squared; if odd, it will be instead be calculated as <c>3 * x - 1</c>. This is a concise way to write conditional assignments in Java. However, you might want to use it sparingly, as it can make code less readable if overused or used with complex expressions.
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</p>
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</section>
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<section xml:id="chapter4_summary">
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<title>Summary &amp; Reading Questions</title>

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