lectures.alex.balgavy.eu

commit e7a225e906cc01d373eb844a7f54ddb903cbc681
parent ec24c6c93b81031c1f87ddb905fb4c36aa46b5ef
Author: Alex Balgavy <alex@balgavy.eu>
Date:   Tue, 17 Aug 2021 11:08:27 +0200

Advanced programming (Java)

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diff --git a/content/_index.md b/content/_index.md
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 ## Subject notes: Year 2
 
 * [Data Structures & Algorithms](dsa-notes/)
+* [Advanced Programming](ap-notes/)
 * [Statistical Methods](stats-notes)
 * [Operating Systems](os-notes)
 * [Intelligent Systems](is-notes/)
diff --git a/content/ap-notes/_index.md b/content/ap-notes/_index.md
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+title = 'Advanced Programming'
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+
+# Advanced Programming
+- [Classes and instantiation](classes-and-instantiation)
+- [Encapsulation](encapsulation)
+- Inheritance
+- Polymorphism
+- Packages
+- Inner/nested classes
+    - private, protected
+- Abstraction
+- Interfaces
+- Exceptions
+- Data structures
+    - enum, hashmap, arraylist, iterator
diff --git a/content/ap-notes/classes-and-instantiation.md b/content/ap-notes/classes-and-instantiation.md
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+title = 'Classes and instantiation'
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+# Advanced Programming
+Classes have the form:
+
+```java
+public class ClassName {
+}
+```
+
+Instantiate classes with `new`:
+
+```java
+ClassName instance = new ClassName();
+```
+
+The name of the Java file should match the class name.
+One (main) class per file.
+
+Access variables via dot syntax: `car.brand`
+
+Instance variables are declared in the body of a class.
+`static` variables and methods are class variables/methods.
+
+Constructors are public, and have the same name as the class:
+
+```java
+public class Main {
+    int x;
+
+    public Main() {
+        x = 42;
+    }
+
+    public static void main(String[] args) {
+        Main myMain = new Main();
+        System.out.printf("The constructor sets the value: %d", myMain.x); // 42
+    }
+}
+```
+
+There are no destructors, as Java is garbage-collected.+
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+title = 'Encapsulation'
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+# Encapsulation
+Encapsulation makes sure that sensitive stuff is hidden from users.
+
+Idea: declare class variables/attributes as private, provide public getters and setters to use the variable.
+
+```java
+public class Safe {
+    private String superPrivateInfo;
+
+    public String getSuperPrivateInfo() {
+        return superPrivateInfo;
+    }
+
+    public void setSuperPrivateInfo(String newInfo) {
+        this.superPrivateInfo = newInfo;
+    }
+}
+```
+
+Classes can be:
+- `public`: accessible by any other class
+- default: only accessible in same package
+
+Attributes/methods/constructors can be:
+- `public`: accessible by any other class
+- `private`: only accessible within declared class
+- default: only accessible in same package
+- `protected`: only accessible in same package and subclasses+
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