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add more notes in java programming
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kekeandzeyu committed Dec 5, 2024
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xsi:noNamespaceSchemaLocation="https://resources.jetbrains.com/writerside/1.0/topic.v2.xsd"
title="Java Programming" id="Java-Programming">

<show-structure for="chapter" depth="3"/>
<chapter title="1 Class Terminology" id="Class-Terminology">
<p>In Java, classes can contain not just functions (a.k.a. methods), but also data.</p>
<p>To run a class, we must define a main method (but not all classes have a main method). Unlike python, there's
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="6-object-oriented-programming" summary="OOP in Python">OOP in Python</a> for basic understanding!
</p>
</note>
<p><format color="IndianRed">Example with Terminology</format></p>
<p>
<format color="IndianRed">Example with Terminology</format>
</p>
<code-block lang="Java" collapsible="true">
/* penguin.java */
public class penguin {
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}
</code-block>
<tip>
<p><format color="BlueViolet">Key differences between static and non-static (a.k.a. instance) members:
</format></p>
<p>
<format color="BlueViolet">Key differences between static and non-static (a.k.a. instance) members:
</format>
</p>
<list type="bullet">
<li>
<p>Static memberss are invoked using the class name, e.g. <code>penguin.makeNoise();</code>,
<code>penguin.binomen</code></p>
<code>penguin.binomen</code></p>
<p>It is acceptible to use instance to invoke static methods (e.g. <code>p1.makeNoise();</code>),
but some compilers and IDEs will issue a warning.</p>
<p>Static methods must access instance variables via a specific instance (
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</li>
</list>
</tip>
<p><format color="BlueViolet">Initialing an array</format></p>
<p>
<format color="BlueViolet">Initialing an array</format>
</p>
<compare first-title="Java" second-title="Python">
<code-block lang="Java">
int[] arr1 = new int[5]; // Array of 5 elements, all initialized to 0
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</code-block>
</compare>
</chapter>
<chapter title="2 Inheritance" id="Inheritance">
<p>Inheritance is a way to create a new class that reuses the properties of an existing class. The new class is
called a subclass, and the existing class is called a superclass.</p>
<p>Java does not support multiple inheritance, but it does support multi-level inheritance.</p>
<p>Subclasses can override methods of the superclass, but they can also call the superclass's method using
<code>super.methodName()</code>.</p>
<p>Subclasses can also call the superclass's constructor using <code>super()</code>.</p>
<p><format color="IndianRed">Example with Inheritance</format></p>
<code-block lang="Java" collapsible="true">
public class Animal {
public void makeNoise() {
System.out.println("Some sound");
}
}

public class Dog extends Animal {
public void makeNoise() {
System.out.println("Bark");
System.out.println("Woof");
}

public void superNoise() {
super.makeNoise();
for (int i = 0; i &lt; 3; i++) {
super.makeNoise();
}
}
}
<chapter title="2 References, Recursion, and Lists" id="2-refernces-recursion-lists">
<p>8 primitive types in Java: <code>byte</code>, <code>short</code>, <code>int</code>, <code>long</code>,
<code>float</code>, <code>double</code>, <code>boolean</code>, <code>char</code>.</p>
<p>Everything else, including arrays, is a reference type.</p>
<p>The <code>new</code> keyword allocates memory on the heap, a region of memory dedicated to dynamic object
allocation. This memory space holds the instance variables (data members) of your new object.</p>
<p>The constructor of the class is then invoked. The constructor's job is to initialize the object's state
by setting the initial values of the instance variables.</p>
<p>Once the constructor completes, new returns a reference (address) to the newly created object.</p>
<p><format color="BlueViolet">The Golden Rule of Equals (and Parameter Passing):</format> Given variables b and
a, b = a copies all the bits from a into b, and passing parameters obeys the same rule.</p>
<note>
<p>There may be a little confusion here: When you pass a primitive type (e.g., <code>int</code>,
<code>float</code>, <code>boolean</code>, etc.) to a method, a copy of the value is made and passed to
the method. Modifying the parameter within the method does not affect the original variable.</p>
<p>When you pass an object to a method, a copy of the reference to the object is passed. The reference
itself is passed by value, but the reference points to the original object on the heap. This means when
you modify the object within the method, the changes are reflected in the original object.</p>
</note>
<p><format color="BlueViolet">Arrays in Java</format></p>
<code-block lang="Java">
int[] a = new int[]{0, 1, 2, 95, 4}; // Declaration &amp; Instantiation
</code-block>
<procedure title="Declaraing &amp; Instantiating Arrays">
<step>
<p>Creates a 64 bit box (reference) for storing an int array address. (declaration)</p>
</step>
<step>
<p>Creates a new Object, in this case an int array. (instantiation)</p>
</step>
<step>
<p>Puts the address of this new Object into the 64 bit box named a. (assignment)</p>
</step>
</procedure>
</chapter>
</topic>

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