Collections.sort(this.arrayList1)

Week 4: Writing classes/12B. Class Letters

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+Write a class 'Letters' that models a set of alphabetic characters (lowercase letters a...z).
+
+Note! Since the 'Test' class is public, 
+the class 'Letters' cannot be - so do not use the public attribute when defining the class!
+
+Each letter can appear in the set at most once. 
+The letters are in alphabetical order.
+
+
+The class has the following public methods:
+The constructor Letters(), which takes no parameters
+method public void addLetter(char letter), which takes as parameter one letter to be added to the set
+Method public void addLetters(String letters), which takes as parameter a string that can contain multiple letters - all letters in the string are added to the set
+Method public String allLetters() which returns all the letters in the set as a single string.
+
+
+Examples of class functionality:
+Letters letters = new Letters();
+letters.addLetter('b');
+letters.addLetter('a');
+letters.addLetter('d');
+System.out.println(letters.allLetters());
+
+// no effect, letter already in the set
+letters.addLetter('b');
+System.out.println(letters.allLetters());
+
+
+letters.addLetters("hfsr");
+System.out.println(letters.allLetters());
+
+// Adds only those letters,
+// that are not yet in the set
+letters.addLetters("abxysr");
+System.out.println(letters.allLetters());
+
+
+Program outputs:
+abd
+abd
+abdfhrs
+abdfhrsxy
+
+
+
+
+
+===========
+
+
+
+import java.util.Random;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Collections;
+
+public class Test{
+    public static void main(String[] args){
+        System.out.println("Testing class Letters");
+        
+        Letters letters = new Letters();
+        
+        System.out.println("Object created!");
+        
+        String chars = "abcxy";
+        for (int i=0; i<chars.length(); i++) {
+            char c = chars.charAt(i);
+            System.out.println("Adding letter: " + c);
+            letters.addLetter(c);
+            System.out.println("Set now: " + letters.allLetters());
+        }
+        
+        System.out.println("");
+        System.out.println("Trying to add letters that are already in the set");
+        
+        chars = "acx";
+        for (int i=0; i<chars.length(); i++) {
+            char c = chars.charAt(i);
+            System.out.println("Adding letter: " + c);
+            letters.addLetter(c);
+            System.out.println("Set now: " + letters.allLetters());
+        }
+        
+        System.out.println("");
+        System.out.println("Adding several letters at once");
+        
+        String[] arr = {"def", "gr", "hsz"};
+        for (String s : arr) {
+            System.out.println("Adding string: " + s);
+            letters.addLetters(s);
+            System.out.println("Set now: " + letters.allLetters());
+        }
+        
+        System.out.println("");
+        System.out.println("Adding several letters that are in the set already");
+        
+        arr = new String[] {"abc", "hij", "prst"};
+        for (String s : arr) {
+            System.out.println("Adding string: " + s);
+            letters.addLetters(s);
+            System.out.println("Set now: " + letters.allLetters());
+        }
+        
+    }
+}
+
+
+
+
+
+
+class Letters {
+    // CLASS ATTRIBUTES
+    private ArrayList<String> letters;
+
+    // CONSTRUCTOR
+    public Letters() {
+        this.letters = new ArrayList<String>();
+    }
+
+    public void addLetter(char letter) {
+        String letterString = String.valueOf(letter);
+        // new set of letters
+        if (letterString.length() < 1) {
+            this.letters.add(letterString);
+        }
+        // add letter if it is not in the set
+        else if (!this.letters.contains(letterString)) {
+            this.letters.add(letterString);
+            // https://www.geeksforgeeks.org/java/arrays-sort-in-java/
+            // 'Arrays' sort had issues
+            // Arrays.sort(this.letters);
+            // move to 'Collections' sort
+            // https://www.baeldung.com/java-arrays-collections-sort-methods
+            Collections.sort(this.letters);
+        }
+        // else, do not add 'letter'
+    }
+
+    public void addLetters(String letters) {
+        // go through each character in the 'letters' string
+        // (converted to a charcaters array)
+        for (char c : letters.toCharArray()) {
+            // call the single letter addition method
+            this.addLetter(c);
+        }
+    }
+
+    public String allLetters() {
+        // convert ArrayList to a string
+        // return this.letters.toString();
+        return String.join("", this.letters);
+    }
+}
+
+
+
+
+
+
+
+
+
+Testing class Letters
+Object created!
+Adding letter: a
+Set now: a
+Adding letter: b
+Set now: ab
+Adding letter: c
+Set now: abc
+Adding letter: x
+Set now: abcx
+Adding letter: y
+Set now: abcxy
+
+Trying to add letters that are already in the set
+Adding letter: a
+Set now: abcxy
+Adding letter: c
+Set now: abcxy
+Adding letter: x
+Set now: abcxy
+
+Adding several letters at once
+Adding string: def
+Set now: abcdefxy
+Adding string: gr
+Set now: abcdefgrxy
+Adding string: hsz
+Set now: abcdefghrsxyz
+
+Adding several letters that are in the set already
+Adding string: abc
+Set now: abcdefghrsxyz
+Adding string: hij
+Set now: abcdefghijrsxyz
+Adding string: prst
+Set now: abcdefghijprstxyz
+
+