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Crashkurs Java im Modul Algorithmen und Datenstrukturen
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01: Hello World
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#1 Einfache Objekte und Veerbung
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#3 static in einer Klasse
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#1 Einfache Objekte und Veerbung
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#2 komplexere Vererbung von Klassen
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#3 static in einer Klasse
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<h1 id="04-einfuhrung-in-objekte">04: Einführung in Objekte</h1>
<h2 id="kurze-begriffserklarung">Kurze Begriffserklärung</h2>
<p>Quelle: <a href="https://stackhowto.com/difference-between-instantiating-declaring-and-initializing/">stackhowto.com</a></p>
<h3 id="declaration">Declaration</h3>
<blockquote>
<p>Declaring a variable means the first “mention” of the variable, which tells the compiler “Hello, I am here and can be used”.
In a statically typed language like Java, this also means that the declared type of the variable is determined.
The value itself is not determined during the declaration.
<div class="highlight"><pre><span></span><code><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="p">;</span><span class="w"></span>
<span class="kt">int</span><span class="w"> </span><span class="n">nbr</span><span class="p">;</span><span class="w"></span>
</code></pre></div></p>
</blockquote>
<h3 id="initialization">Initialization</h3>
<blockquote>
<p>The term initialization usually means the first assignment of a value to a variable.
<div class="highlight"><pre><span></span><code><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Thomas&quot;</span><span class="p">;</span><span class="w"></span>
<span class="kt">int</span><span class="w"> </span><span class="n">nbr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w"></span>
</code></pre></div></p>
</blockquote>
<h3 id="instantiation">Instantiation</h3>
<blockquote>
<p>The term instantiation actually has nothing to do with assigning a value to a variable, even if a new object is sometimes instantiated when a variable is initialized.
The term simply means the creation of a new object, i.e. an instance, from a class.
<div class="highlight"><pre><span></span><code><span class="n">String</span><span class="w"> </span><span class="n">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">String</span><span class="p">(</span><span class="s">&quot;Thomas&quot;</span><span class="p">);</span><span class="w"></span>
</code></pre></div></p>
</blockquote>
<h2 id="modifier">Modifier</h2>
<p>Quelle: <a href="https://www.w3schools.com/java/java_modifiers.asp">w3schools.com</a></p>
<h3 id="access-modifier">Access-Modifier</h3>
<table>
<thead>
<tr>
<th>Modifier</th>
<th>Beschreibung</th>
</tr>
</thead>
<tbody>
<tr>
<td>public</td>
<td>The code is accessible for all classes</td>
</tr>
<tr>
<td>private</td>
<td>The code is only accessible within the declared class</td>
</tr>
<tr>
<td>protected</td>
<td>The code is accessible in the same package and subclasses.</td>
</tr>
<tr>
<td>default</td>
<td>The code is only accessible in the same package. This is used when you don't specify a modifier.</td>
</tr>
</tbody>
</table>
<h3 id="non-access-modifier">Non-Access-Modifier</h3>
<table>
<thead>
<tr>
<th>Modifier</th>
<th>Beschreibung</th>
</tr>
</thead>
<tbody>
<tr>
<td>final</td>
<td>The class cannot be inherited by other classes</td>
</tr>
<tr>
<td>abstract</td>
<td>The class cannot be used to create objects (To access an abstract class, it must be inherited from another class.</td>
</tr>
</tbody>
</table>
<h2 id="1-einfache-objekte-und-veerbung">#1 Einfache Objekte und Veerbung</h2>
<p><strong>Lernziele:</strong>
* eine Klasse erzeugen
* eine Klasse aufrufen
* einfache Veerbung
* Polymorphie (Überschreiben von Methoden)
* die Verwendung von <code>this</code>
* die Verwendung von <code>super</code></p>
<div class="highlight"><pre><span></span><code><span class="c1">// main.java</span><span class="w"></span>
<span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Main</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">Animal</span><span class="w"> </span><span class="n">myAnimal</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Animal</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">myAnimal</span><span class="p">.</span><span class="na">makeSound</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">Dog</span><span class="w"> </span><span class="n">myDog</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Dog</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">myDog</span><span class="p">.</span><span class="na">makeSound</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">Cat</span><span class="w"> </span><span class="n">myCat</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Cat</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">myCat</span><span class="p">.</span><span class="na">makeSound</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">myCat</span><span class="p">.</span><span class="na">compareToAnimal</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</code></pre></div>
<div class="highlight"><pre><span></span><code><span class="c1">// Animal.java</span><span class="w"></span>
<span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Animal</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kt">boolean</span><span class="w"> </span><span class="n">isPet</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="nf">Animal</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;## in constructor of Animal&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">isPet</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">false</span><span class="p">;</span><span class="w"> </span><span class="c1">// it doesn&#39;t exist for our cats or dogs</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">makeSound</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;Yes, animal usually make sounds&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</code></pre></div>
<p><div class="highlight"><pre><span></span><code><span class="c1">// Cat.java</span><span class="w"></span>
<span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Cat</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Animal</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="nf">Cat</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;## in constructor of Cat&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">isPet</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="nd">@Override</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">makeSound</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;meow meow&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">compareToAnimal</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;--- Animal ---&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="kd">super</span><span class="p">.</span><span class="na">makeSound</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;is alive: &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="kd">super</span><span class="p">.</span><span class="na">isPet</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;--- Cat ---&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">makeSound</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;is alive: &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">isPet</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</code></pre></div>
<div class="highlight"><pre><span></span><code><span class="c1">// Dog.java</span><span class="w"></span>
<span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Dog</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Animal</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="nf">Dog</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;## in constructor of Dog&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">isPet</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="nd">@Override</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">makeSound</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;woof woof&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">isPet</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">compareToAnimal</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;--- Animal ---&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="kd">super</span><span class="p">.</span><span class="na">makeSound</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;is alive: &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="kd">super</span><span class="p">.</span><span class="na">isPet</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;--- Cat ---&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">makeSound</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;is alive: &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">isPet</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</code></pre></div></p>
<h2 id="2-komplexere-vererbung-von-klassen">#2 komplexere Vererbung von Klassen</h2>
<p><strong>Lernziele:</strong>
* Erweiterte Veerbung
* Modifikatoren für Attribute
* Getter und Setter
* Konstruktorverkettung</p>
<div class="highlight"><pre><span></span><code><span class="c1">// main.java</span><span class="w"></span>
<span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Main</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">Vehicle</span><span class="w"> </span><span class="n">myVehicle</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Vehicle</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;-- myVehicle:&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;number of wheels: &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">myVehicle</span><span class="p">.</span><span class="na">getNumberOfWheels</span><span class="p">());</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;max Speed: &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">myVehicle</span><span class="p">.</span><span class="na">getMaxSpeed</span><span class="p">());</span><span class="w"></span>
<span class="w"> </span><span class="n">myVehicle</span><span class="p">.</span><span class="na">setMaxSpeed</span><span class="p">(</span><span class="mi">150</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;max Speed: &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">myVehicle</span><span class="p">.</span><span class="na">getMaxSpeed</span><span class="p">());</span><span class="w"></span>
<span class="w"> </span><span class="n">Car</span><span class="w"> </span><span class="n">myCar</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Car</span><span class="p">(</span><span class="s">&quot;blue&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;-- myCar:&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;number of wheels: &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">myCar</span><span class="p">.</span><span class="na">getNumberOfWheels</span><span class="p">());</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;max Speed: &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">myCar</span><span class="p">.</span><span class="na">getMaxSpeed</span><span class="p">());</span><span class="w"></span>
<span class="w"> </span><span class="n">myVehicle</span><span class="p">.</span><span class="na">setMaxSpeed</span><span class="p">(</span><span class="mi">150</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;max Speed: &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">myCar</span><span class="p">.</span><span class="na">getMaxSpeed</span><span class="p">());</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</code></pre></div>
<div class="highlight"><pre><span></span><code><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Vehicle</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="kd">protected</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">numberOfWheels</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="kd">protected</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">maxSpeed</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="nf">Vehicle</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;## in default constructor of Vehicle&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">numberOfWheels</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">maxSpeed</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">100</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="nf">Vehicle</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">numberOfWheels</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">maxSpeed</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;## in constructor of Vehicle&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">numberOfWheels</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">numberOfWheels</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">maxSpeed</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">maxSpeed</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">getNumberOfWheels</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">numberOfWheels</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">getMaxSpeed</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">maxSpeed</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="nf">printMaxSpeed</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">maxSpeed</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">&quot; km/h&quot;</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">setMaxSpeed</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">newMaxSpeed</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">newMaxSpeed</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="k">return</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">maxSpeed</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">newMaxSpeed</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</code></pre></div>
<div class="highlight"><pre><span></span><code><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Car</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Vehicle</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="kd">private</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="n">color</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="nf">Car</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">color</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="kd">super</span><span class="p">(</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p">);</span><span class="w"> </span><span class="c1">// always needs to be the first statement</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;## in constructor of Car&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">color</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">color</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="nd">@Override</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">setMaxSpeed</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">newMaxSpeed</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">newMaxSpeed</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">1000</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;No car shall be this slow tbh&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">return</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">maxSpeed</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">newMaxSpeed</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</code></pre></div>
<div class="highlight"><pre><span></span><code><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Car</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Vehicle</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="kd">private</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="n">color</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="nf">Car</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">color</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="kd">super</span><span class="p">(</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p">);</span><span class="w"> </span><span class="c1">// always needs to be the first statement</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;## in constructor of Car&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">color</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">color</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="nd">@Override</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">setMaxSpeed</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">newMaxSpeed</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">newMaxSpeed</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">1000</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;No car shall be this slow tbh&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">return</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">maxSpeed</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">newMaxSpeed</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</code></pre></div>
<div class="highlight"><pre><span></span><code><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Truck</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Vehicle</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="kd">private</span><span class="w"> </span><span class="kt">boolean</span><span class="w"> </span><span class="n">isFireTruck</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="kd">private</span><span class="w"> </span><span class="kd">final</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="n">hornSound</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="nf">Truck</span><span class="p">(</span><span class="kt">boolean</span><span class="w"> </span><span class="n">isFireTruck</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="kd">super</span><span class="p">(</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p">);</span><span class="w"> </span><span class="c1">// always needs to be the first statement</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;## in constructor of Truck&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">isFireTruck</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">isFireTruck</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">hornSound</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;test&quot;</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kt">boolean</span><span class="w"> </span><span class="nf">getIsFireTruck</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">isFireTruck</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</code></pre></div>
<h2 id="3-static-in-einer-klasse">#3 <code>static</code> in einer Klasse</h2>
<p><strong>Lernziele:</strong>
* statische und dynamische Variablen
* statische und dynamische Methoden</p>
<div class="highlight"><pre><span></span><code><span class="c1">// main.java</span><span class="w"></span>
<span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Main</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="n">String</span><span class="o">[]</span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">Counter</span><span class="p">.</span><span class="na">printCounterStatic</span><span class="p">(</span><span class="s">&quot;Static&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">Counter</span><span class="p">.</span><span class="na">increaseCounterStatic</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">Counter</span><span class="p">.</span><span class="na">printCounterStatic</span><span class="p">(</span><span class="s">&quot;Static&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">Counter</span><span class="w"> </span><span class="n">myCounter</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Counter</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">Counter</span><span class="p">.</span><span class="na">increaseCounterStatic</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">myCounter</span><span class="p">.</span><span class="na">increaseCounterDynamic</span><span class="p">();</span><span class="w"></span>
<span class="w"> </span><span class="n">myCounter</span><span class="p">.</span><span class="na">printCounterDynamic</span><span class="p">(</span><span class="s">&quot;Dynamic&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</code></pre></div>
<div class="highlight"><pre><span></span><code><span class="kd">public</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Counter</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">counterValueStatic</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">counterValueDynamic</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">increaseCounterStatic</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">counterValueStatic</span><span class="o">++</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">increaseCounterDynamic</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">counterValueDynamic</span><span class="o">++</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">printCounterDynamic</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">classID</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;&gt;&gt; execute printCounterDynamic of class &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">classID</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;static: &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">counterValueStatic</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;dynamic: &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="k">this</span><span class="p">.</span><span class="na">counterValueDynamic</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="w"> </span><span class="kd">public</span><span class="w"> </span><span class="kd">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">printCounterStatic</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="n">classID</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;&gt;&gt; execute printCounterStatic of class &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">classID</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">System</span><span class="p">.</span><span class="na">out</span><span class="p">.</span><span class="na">println</span><span class="p">(</span><span class="s">&quot;dynamic: &quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">counterValueStatic</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</code></pre></div>
<hr>
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<small>
Letztes Update:
<span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-datetime">November 4, 2022 16:13:00</span>
<br>
Erstellt:
<span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-datetime">November 2, 2022 20:46:05</span>
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<small>
Authors: <span class='git-page-authors git-authors'><a href='mailto:yamidoesdev@gmail.com'>YamiDoesDev</a></span>
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