Create 11A Other object methods (beyond get/set)

Week 4: Writing classes/11A Other object methods (beyond get/set)

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+Of course, object methods do not have to be just straightforward methods 
+for setting and observing attributes. 
+However, in general, methods do make some use of attributes; 
+the purpose of public operations on objects is to view and modify the 
+data content of the object.
+
+
+Consider the class 'Notebook'. 
+Since notes are a list, it would be more convenient than a 
+direct setting method to provide a method for the client to 
+'add a single note to the notebook':
+
+class Notebook {
+    private String owner;
+    private ArrayList<String> notes;
+
+    // CONSTRUCTOR
+    public Notebook(String owner) {
+        this.owner= owner;
+        // not from parameter, but initialize an empty list
+        this.notes= new ArrayList<>();
+    }
+    
+    public String getOwner() {
+        return this.owner;
+    }
+    
+    public void addNote(String note) {
+        this.notes.add(note);
+    }
+    
+    // Returns all notes in one string
+    public String allNotes() {
+        // join method connects all elements of the list with 
+        // the given separator
+        // kind of like the opposite of 'split' method
+        String nb = String.join("\n", notes);
+        return nb;
+    }
+}
+
+
+Now it's easier for the customer to use the notebook. 
+The actual storage format is encapsulated (i.e. hidden from the client). 
+This means that it doesn't matter if the internal implementation of 
+the class changes (for example, from a list to a table or a hash table)
+as long as the public operations are preserved.
+
+public class Testclass {
+    public static void main(String[] args) {
+        Notebook book = new Notebook("Mike Memorizer");
+        book.addNote("Go to the store!");
+        book.addNote("Cram for test!");
+        book.addNote("Watch the news!");
+        
+        System.out.println(book.allNotes());
+    }
+}
+
+Program outputs:
+Go to the store!
+Cram for test!
+Watch the news!
+
+
+
+
+
+
+
+
+ 
+As another example, consider the class 'Cube'. 
+In addition to methods for setting and getting the length of a page, 
+the class could have methods for calculating the area and volume, for example:
+
+class Cube {
+    private int sidelength;
+
+    // constructor
+    public Cube(int sidelength) {
+        this.sidelength = sidelength;
+    }
+
+    public int getSidelength() {
+        return sidelength;
+    }
+
+    public void setSidelength(int sidelength) {
+        this.sidelength= sidelength;
+    }
+    
+    public int Area() {
+        return sidelength* sidelength* 6;
+    }
+    
+    public int Volume() {
+        return sidelength * sidelength* sidelength;
+    }   
+}
+
+Example on using the class:
+public class TestClass {
+    public static void main(String[] args) {
+        Cube smallCube = new Cube(3);
+        System.out.println(smallCube.Area());
+        System.out.println(smallCube.Volume());
+        
+        Cube largeCube = new Cube(15);
+        System.out.println(largeCube.Area());
+        System.out.println(largeCube.Volume());        
+    }
+}
+
+Program outputs:
+54
+27
+1350
+3375
+
+
+