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161 lines
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HTML
161 lines
5.6 KiB
HTML
<!DOCTYPE html>
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<article class="article">
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<h1>Lecture for January 25</h1>
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<h2>Strings</h2>
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<p>These are concatenated chars</p>
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<pre><code class="language-java">'d' + 'o' + 'g' // equivalent to "dog"</code></pre>
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<pre><code class="language-java">"straw" + "berry" // strawberry</code></pre>
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<p>Strings are denoted by double quotes <code>""</code> rather than a string which is denoted by single quotes <code>''</code></p>
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<p>String is not a primitive type, it is a class. Hence, why it is capitalized in Java.</p>
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<p>The <code>java.lang.String</code> is automatically imported in Java.</p>
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<p>To declare and initialize a String</p>
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<pre><code class="language-java">String name = "Henry";</code></pre>
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<p>In memory it appears as</p>
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<table>
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<thead>
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<tr>
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<th>H</th>
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<th>'e'</th>
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<th>'n'</th>
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<th>'r'</th>
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<th>'y'</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td></td>
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<td></td>
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<h3>String Methods</h3>
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<pre><code class="language-java">int length()</code></pre>
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<pre><code class="language-java">boolean equals(String another)</code></pre>
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<pre><code class="language-java">boolean startsWith(String prefix)</code></pre>
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<pre><code class="language-java">boolean endsWith(String suffix)</code></pre>
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<pre><code class="language-java">String substring(int start, int end)</code></pre>
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<pre><code class="language-java">int indexOf(int ch)</code></pre>
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<pre><code class="language-java">String toLowerCase()</code></pre>
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<h3>Using String Methods</h3>
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<pre><code class="language-java">char first = name.charAt(0);</code></pre>
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<p>Remember in Java, that it starts counting from zero! If you try to access a letter that doesn't exist, it will produce an <code>IndexOutOfBounds</code> error.</p>
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<h2>Errors</h2>
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<p>There are two types of errors, compile-type errors and run-time errors. Later we will talk about debugging skills such as making "breakpoints" in your code so you can analyze the different variable values.</p>
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<h3>Compile Time Errors</h3>
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<p>Compile time errors are generated due to syntax errors. Forgot a semicolon? Missing a brace? </p>
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<h3>Run-time Errors</h3>
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<p>These are logic errors. Not derived from syntax errors. An example of one that was discussed earlier is the <code>IndexOutOfBounds</code> error.</p>
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<h2>Tricky Thing About Input</h2>
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<p>Let's talk about input right now. Let's say you have the following scenario</p>
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<pre><code class="language-java">Scanner input = new Scanner(System.in);
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System.out.println("Enter pet's age: ");
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int age = input.nextInt();
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System.out.println("Enter pet's name: ");
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String name = input.nextLine();
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System.out.println("Enter pet's breed: ");
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String breed = input.next();</code></pre>
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<p>Then when we start to run the program...</p>
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<pre><code class="language-reStructuredText">Enter pet's age:
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14
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Enter pet's name:
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Enter pet's breed:
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Labradoodle</code></pre>
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<p>Why did it skip pet's name? Let's run through the process again</p>
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<pre><code class="language-reStructuredText">Enter pet's age:
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14 [ENTER]
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Enter pet's name:
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Enter pet's breed:
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Labradoodle</code></pre>
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<p>Here the [ENTER] key gets saved into name.</p>
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<p>To resolve this, just use an <code>input.nextLine()</code> to throw away that [ENTER]</p>
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<pre><code class="language-java">Scanner input = new Scanner(System.in);
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System.out.println("Enter pet's age: ");
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int age = input.nextInt();
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System.out.println("Enter pet's name: ");
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input.nextLine();
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String name = input.nextLine();
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System.out.println("Enter pet's breed: ");
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String breed = input.next();</code></pre>
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</article>
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