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<h1 style="margin-bottom:0;padding-bottom:0;">A Java development cheatsheet for my classmates</h1>
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<em>PROG10082: Reference Material</em>
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<br><br>
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<p>This document is written for my PROG10082 classmates as a quick reference for some Java concepts that were skipped over in the course. This document may be updated as needed.</p>
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<h2 id="vscode-tips">VSCode Tips</h2>
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<p><em>Remember</em>, you can open <a rel="noopener" target="_blank" href="https://code.visualstudio.com/docs/editor/intellisense">intelisense</a> by pressing <kbd>Ctrl</kbd> + <kbd>Space</kbd>. This is a super handy tool for auto-complete in your code no matter the language you are working in.</p>
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<p>Typing the following then opening intelisense will give you some shorthand options for quickly typing common code. Just select the option you want with arrow keys, and press <kbd>Enter</kbd> to apply it.</p>
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<table><thead><tr><th>Shortcut</th><th>Description</th></tr></thead><tbody>
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<tr><td><code>syso</code></td><td>Automatically print <code>System.out.println();</code></td></tr>
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<tr><td><code>syserr</code></td><td>Automatically print <code>System.err.println();</code></td></tr>
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</tbody></table>
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<h2 id="upper-and-lowercase-types">Upper and lowercase types</h2>
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<p>Many types you encounter in Java have an uppercase and lowercase variant, for example <code>int</code> and <code>Integer</code>. The difference is important. Here are the avalible uppercase variants of common types:</p>
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<table><thead><tr><th>Standard type</th><th>Uppercase type</th></tr></thead><tbody>
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<tr><td><code>short</code></td><td><code>Short</code></td></tr>
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<tr><td><code>char</code></td><td><code>Character</code></td></tr>
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<tr><td><code>byte</code></td><td><code>Byte</code></td></tr>
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<tr><td><code>int</code></td><td><code>Integer</code></td></tr>
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<tr><td><code>double</code></td><td><code>Double</code></td></tr>
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<tr><td><code>float</code></td><td><code>Float</code></td></tr>
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<tr><td><code>long</code></td><td><code>Long</code></td></tr>
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</tbody></table>
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<h3 id="null-and-optional-values">Null and optional values</h3>
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<p>One uses of the uppercase variant of a type is to allow <code>null</code> values. In most languages, <code>null</code> means "Nothing". In Java, you can use <code>null</code> to indicate that a variable is not yet assigned a value. This can be checked with the <code>==</code> operator.</p>
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<p>An example usage of this could be the following:</p>
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<pre data-lang="java" style="background-color:#2b303b;color:#c0c5ce;" class="language-java "><code class="language-java" data-lang="java"><span style="color:#65737e;">// We want to ask for a number of records to read
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</span><span style="color:#ebcb8b;">Scanner</span><span> input = </span><span style="color:#b48ead;">new </span><span style="color:#ebcb8b;">Scanner</span><span>(</span><span style="color:#ebcb8b;">System</span><span>.in);
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</span><span style="color:#b48ead;">int</span><span> recordCount = input.</span><span style="color:#bf616a;">nextInt</span><span>();
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</span><span>
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</span><span style="color:#65737e;">// Create a value to store the highest record in
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</span><span style="color:#65737e;">// I have made this `null` so we can know if we didnt get a value
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</span><span style="color:#ebcb8b;">Integer</span><span> highestRecord = </span><span style="color:#d08770;">null</span><span>;
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</span><span>
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</span><span style="color:#65737e;">// Read the records
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</span><span style="color:#b48ead;">for </span><span>(</span><span style="color:#b48ead;">int</span><span> i = </span><span style="color:#d08770;">0</span><span>; i < recordCount; i++) {
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</span><span> </span><span style="color:#65737e;">// Read a value
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</span><span> </span><span style="color:#b48ead;">int</span><span> record = input.</span><span style="color:#bf616a;">nextInt</span><span>();
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</span><span>
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</span><span> </span><span style="color:#65737e;">// If the value is higher than the current highest record
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</span><span> </span><span style="color:#65737e;">// or the highest record is `null`, update the highest record
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</span><span> </span><span style="color:#b48ead;">if </span><span>(highestRecord == </span><span style="color:#d08770;">null </span><span>|| record > highestRecord) {
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</span><span> highestRecord = record;
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</span><span> }
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</span><span>}
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</span><span>
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</span><span style="color:#65737e;">// We now have the highest record
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</span><span style="color:#b48ead;">if </span><span>(highestRecord != </span><span style="color:#d08770;">null</span><span>) {
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</span><span> </span><span style="color:#ebcb8b;">System</span><span>.out.</span><span style="color:#bf616a;">println</span><span>("</span><span style="color:#a3be8c;">The highest record is </span><span>" + highestRecord);
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</span><span>} </span><span style="color:#b48ead;">else </span><span>{
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</span><span> </span><span style="color:#ebcb8b;">System</span><span>.out.</span><span style="color:#bf616a;">println</span><span>("</span><span style="color:#a3be8c;">No records were entered</span><span>");
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</span><span>}
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</span></code></pre>
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<h3 id="pass-by-reference">Pass-by-reference</h3>
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<p>Another use of uppercase types is pass-by-reference. </p>
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<pre data-lang="java" style="background-color:#2b303b;color:#c0c5ce;" class="language-java "><code class="language-java" data-lang="java"><span style="color:#65737e;">// This is a function that will try to add `1` to a value
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</span><span>void </span><span style="color:#bf616a;">addOne</span><span>(</span><span style="color:#b48ead;">int</span><span> value) {
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</span><span> value = value + </span><span style="color:#d08770;">1</span><span>;
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</span><span>}
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</span><span>
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</span><span>void </span><span style="color:#bf616a;">main</span><span>(</span><span style="color:#ebcb8b;">String </span><span>...args) {
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</span><span> </span><span style="color:#65737e;">// We can make a value
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</span><span> </span><span style="color:#b48ead;">int</span><span> myNumber = </span><span style="color:#d08770;">1</span><span>;
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</span><span>
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</span><span> </span><span style="color:#65737e;">// And pass it to a function. You would expect this to work
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</span><span> </span><span style="color:#bf616a;">addOne</span><span>(myNumber);
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</span><span>
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</span><span> </span><span style="color:#65737e;">// But at this point, `myNumber` is still `1`
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</span><span>}
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</span></code></pre>
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<p>Now, we can switch to using uppercase types to make the function edit the value.</p>
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<pre data-lang="java" style="background-color:#2b303b;color:#c0c5ce;" class="language-java "><code class="language-java" data-lang="java"><span style="color:#65737e;">// This is a function that will try to add `1` to a value
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</span><span>void </span><span style="color:#bf616a;">addOne</span><span>(</span><span style="color:#ebcb8b;">Integer</span><span> value) {
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</span><span> value = value + </span><span style="color:#d08770;">1</span><span>;
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</span><span>}
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</span><span>
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</span><span>void </span><span style="color:#bf616a;">main</span><span>(</span><span style="color:#ebcb8b;">String </span><span>...args) {
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</span><span> </span><span style="color:#65737e;">// We can make a value
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</span><span> </span><span style="color:#ebcb8b;">Integer</span><span> myNumber = </span><span style="color:#d08770;">1</span><span>;
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</span><span>
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</span><span> </span><span style="color:#65737e;">// And pass it to a function. This will work, since we have an upprcase type
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</span><span> </span><span style="color:#bf616a;">addOne</span><span>(myNumber);
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</span><span>
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</span><span> </span><span style="color:#65737e;">// At this point, `myNumber` is now `2`
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</span><span>}
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</span></code></pre>
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