collections complete

src/main/java/Collections/Practice/CollectionBasics.java

@@ -2,6 +2,7 @@
 
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.HashSet;
 
 public class CollectionBasics {
     public static void main(String[] args) {
@@ -34,6 +35,15 @@ public static int sum(Collection<Integer> numbers) {
         // Loop through the collection
         // Add each number to total
 
+
+        //loop through each item in numbers
+        for(int item :numbers){
+
+            //add each item in loop to the total
+            total = total + item;
+        }
+
+        //return final total value
         return total;
     }
 
@@ -50,6 +60,15 @@ public static int countEven(Collection<Integer> numbers) {
         // Loop through the collection
         // If the number is even, increase count
 
+        //loop through each item in numbers
+        for(int item : numbers){
+
+            //if item is divisible by 2 (remainder of item / 2 is equal to 0)
+            //then increment count by 1.
+            if(item % 2 ==0){
+                count++;
+            }
+        }
         return count;
     }
 
@@ -65,8 +84,16 @@ public static int findMax(Collection<Integer> numbers) {
         // TODO:
         // Loop through numbers
         // Update max if current number is larger
+        for(int item : numbers){
+            //if item is greater than max
+            if(item > max){
+                //set max to item
+                max = item;
+            }
+        }
+
 
-        return max;
+            return max;
     }
 
 
@@ -81,7 +108,20 @@ public static boolean hasDuplicates(Collection<Integer> numbers) {
         // Hint:
         // Compare the size of a collection with the size of a Set
 
-        return false;
+        //make new set, populate set with values in numbers.
+        //so this set will be a numbers list but without duplicates.
+
+        HashSet<Integer> set = new HashSet<>();
+
+        //add to set for each item in numbers
+        //but there is something that a
+        // set returns when you add something to a set, and its already in the set.
+        for(int item : numbers){
+
+
+        }
+
+            return false;
     }
 
 

src/main/java/Hierachy/PRACTICE.md

@@ -16,7 +16,7 @@ B. Iterable
 C. List  
 D. Queue
 
----
+Answer :B.
 
 ## Question 2
 
@@ -27,7 +27,7 @@ B. Collection
 C. Map  
 D. Deque
 
----
+Answer :B.
 
 ## Question 3
 
@@ -38,7 +38,7 @@ B. Set
 C. Queue  
 D. Map
 
----
+Answer :D.
 
 ## Question 4
 
@@ -49,7 +49,8 @@ B. List
 C. Queue  
 D. TreeSet
 
----
+Answer :B.
+
 
 ## Question 5
 
@@ -60,17 +61,18 @@ B. Set
 C. Queue  
 D. Map
 
----
+Answer :D.
+
 
 # True or False
 
 Write **True** or **False**.
 
-1. `ArrayList` implements the `List` interface.  
-2. `Set` allows duplicate elements.  
-3. `Map` stores elements using keys and values.  
-4. `Queue` typically follows FIFO behavior.  
-5. `Iterable` allows collections to be used in enhanced for-loops.
+1. `ArrayList` implements the `List` interface.  Answer : True
+2. `Set` allows duplicate elements.  Answer : False
+3. `Map` stores elements using keys and values.  Answer : True
+4. `Queue` typically follows FIFO behavior.  Answer : True
+5. `Iterable` allows collections to be used in enhanced for-loops. Answer : True
 
 ---
 
@@ -80,13 +82,13 @@ Write **True** or **False**.
 
 What is the difference between an **interface** and a **class** in the Java Collections Framework?
 
----
+Answer: Interface defines behaviors and class implements those behaviors
 
 ## Question 2
 
 Why is it recommended to declare variables using interfaces like `List` instead of concrete classes like `ArrayList`?
 
-Example:
+Answer: It provides better flexibilities, abstraction and better code design.
 
 ```java
 List<String> list = new ArrayList<>();
@@ -97,8 +99,9 @@ List<String> list = new ArrayList<>();
 ## Question 3
 
 Name three interfaces that extend `Collection`.
+Answer: Lists, Set, and Queue.
+
 
----
 
 # Code Reading Exercise
 
@@ -117,10 +120,9 @@ for (String fruit : fruits) {
 
 Questions:
 
-1. Which interface type is used for the variable?
-2. Which class is used as the implementation?
-3. Why can the enhanced for-loop be used here?
-
+1. Which interface type is used for the variable? Answer: List
+2. Which class is used as the implementation? Answer: ArrayList
+3. Why can the enhanced for-loop be used here? Answer:Lists extends Collections which extends iterable and the enhanced for loop can be used for on all collections.
 ---
 
 # Coding Exercise

src/main/java/Iterable/Examples/ForEachLoopDemo.java

@@ -5,7 +5,6 @@
 
 public class ForEachLoopDemo {
     public static void main(String[] args) {
-
         List<String> students = new ArrayList<>();
 
         students.add("Alex");
@@ -15,23 +14,27 @@ public static void main(String[] args) {
 
         System.out.println("Printing students using a for-each loop:");
 
-        // TODO:
-        // Use a for-each loop to print each student name
-
+// Loop through each student and print their name
+        for (String student : students) {
+            System.out.println(student);
+        }
 
         System.out.println("\nPrinting students in uppercase:");
 
-        // TODO:
-        // Use a for-each loop to print each name in uppercase
-
+// Loop through each student and print name in uppercase
+        for (String student : students) {
+            System.out.println(student.toUpperCase());
+        }
 
         System.out.println("\nCount the number of students:");
 
         int count = 0;
 
-        // TODO:
-        // Use a for-each loop to count how many students are in the list
+// Loop through students and increment count
+        for (String student : students) {
+            count++;
+        }
 
         System.out.println("Total students: " + count);
     }
-}
+}

src/main/java/Iterable/Examples/IteratorDemo.java

@@ -6,7 +6,6 @@
 
 public class IteratorDemo {
     public static void main(String[] args) {
-
         List<Integer> numbers = new ArrayList<>();
 
         numbers.add(10);
@@ -18,26 +17,33 @@ public static void main(String[] args) {
         System.out.println("Original list:");
         System.out.println(numbers);
 
-        // Create iterator
+// Create iterator
         Iterator<Integer> iterator = numbers.iterator();
 
         System.out.println("\nIterating using Iterator:");
 
-        // TODO:
-        // Use iterator.hasNext() and iterator.next()
-        // Print each number
+// Loop through list using iterator
+        while (iterator.hasNext()) {
 
+            int number = iterator.next(); // get next number
+            System.out.println(number);   // print it
+        }
 
         System.out.println("\nRemoving odd numbers using Iterator");
 
         iterator = numbers.iterator();
 
-        // TODO:
-        // Use iterator to remove odd numbers
-        // Remember: use iterator.remove()
+// Remove odd numbers
+        while (iterator.hasNext()) {
+
+            int number = iterator.next();
 
+            if (number % 2 != 0) { // check if number is odd
+                iterator.remove(); // remove it safely
+            }
+        }
 
         System.out.println("\nUpdated list:");
         System.out.println(numbers);
     }
-}
+}

src/main/java/Iterable/Practice/IterableWarmups.java

@@ -4,32 +4,18 @@
 import java.util.List;
 
 public class IterableWarmups {
-    public static void main(String[] args) {
-
-        List<Integer> numbers = new ArrayList<>();
-
-        numbers.add(3);
-        numbers.add(7);
-        numbers.add(10);
-        numbers.add(4);
-        numbers.add(8);
-
-        System.out.println("Sum: " + sum(numbers));
-        System.out.println("Even count: " + countEven(numbers));
-        System.out.println("Max value: " + findMax(numbers));
-    }
-
-
     /*
-    PROBLEM 1
-    Return the sum of all numbers in the iterable
-     */
+ PROBLEM 1
+ Return the sum of all numbers in the iterable
+ */
     public static int sum(Iterable<Integer> numbers) {
 
         int total = 0;
 
-        // TODO:
-        // Use a for-each loop to calculate the sum
+        // Loop through each number in the iterable
+        for (int num : numbers) {
+            total += num; // add each number to total
+        }
 
         return total;
     }
@@ -38,14 +24,19 @@ public static int sum(Iterable<Integer> numbers) {
     /*
     PROBLEM 2
     Count how many numbers are even
-     */
+    */
     public static int countEven(Iterable<Integer> numbers) {
 
         int count = 0;
 
-        // TODO:
-        // Loop through numbers
-        // Increment count if number is even
+        // Loop through each number
+        for (int num : numbers) {
+
+            // Check if the number is even
+            if (num % 2 == 0) {
+                count++; // increase counter
+            }
+        }
 
         return count;
     }
@@ -54,14 +45,19 @@ public static int countEven(Iterable<Integer> numbers) {
     /*
     PROBLEM 3
     Return the maximum value
-     */
+    */
     public static int findMax(Iterable<Integer> numbers) {
 
         int max = Integer.MIN_VALUE;
 
-        // TODO:
         // Loop through numbers
-        // Update max if current number is larger
+        for (int num : numbers) {
+
+            // If current number is greater than max
+            if (num > max) {
+                max = num; // update max
+            }
+        }
 
         return max;
     }
@@ -70,15 +66,20 @@ public static int findMax(Iterable<Integer> numbers) {
     /*
     PROBLEM 4 (BONUS)
     Count how many times a word appears
-     */
+    */
     public static int countMatches(Iterable<String> words, String target) {
 
         int count = 0;
 
-        // TODO:
-        // Loop through words
-        // Compare each word to target
+        // Loop through each word
+        for (String word : words) {
+
+            // Compare word to target
+            if (word.equals(target)) {
+                count++;
+            }
+        }
 
         return count;
     }
-}
+}