De-rusted my Java skills.

src/ArrayPractice.java

@@ -1,17 +1,34 @@
+import java.util.Arrays;
+
 public class ArrayPractice {
   public static void main(String[] args) {
     // Create an array of Strings of size 4
+    int[] nums = new int[4];
 
     // Set the value of the array at each index to be a different String
     // It's OK to do this one-by-one
+    for (int i = 0; i < nums.length; i++) {
+      nums[i] = i+1;
+    }
+    System.out.println(Arrays.toString(nums));
 
     // Get the value of the array at index 2
+    System.out.println(nums[2]);
 
     // Get the length of the array
-
+    System.out.println(nums.length);
+    System.out.println();
+
     // Iterate over the array using a traditional for loop and print out each item
+    for (int i = 0; i < nums.length; i++) {
+      System.out.println(nums[i]);
+    }
+    System.out.println();
 
     // Iterate over the array using a for-each loop and print out each item
+    for (int i : nums) {
+      System.out.println(i);
+    }
 
     /*
      * Reminder!

src/ListPractice.java

@@ -1,27 +1,46 @@
-public class ListPractice {
-
+import java.util.ArrayList;
+import java.util.Collections;
 
+public class ListPractice {
   public static void main(String[] args) {
     // Create an empty ArrayList of Strings and assign it to a variable of type List
+    ArrayList<String> myList = new ArrayList<>();
 
     // Add 3 elements to the list (OK to do one-by-one)
+    myList.add("Hello");
+    myList.add("Oi");
+    myList.add("Bonjour");
 
     // Print the element at index 1
+    System.out.println(myList.get(1));
 
     // Replace the element at index 1 with a new value
     // (Do not insert a new value. The length of the list should not change)
+    myList.set(1, "Hola");
+    System.out.println(myList);
 
     // Insert a new element at index 0 (the length of the list will change)
+    myList.add(0, "Konichiwa");
+    System.out.println(myList);
 
     // Check whether the list contains a certain string
+    System.out.println(myList.contains("Bonjour"));
 
     // Iterate over the list using a traditional for-loop.
     // Print each index and value on a separate line
+    for (int i = 0; i < myList.size(); i++) {
+      System.out.println(i + " - " + myList.get(i));
+    }
 
     // Sort the list using the Collections library
+    Collections.sort(myList);
+    System.out.println(myList);
 
     // Iterate over the list using a for-each loop
     // Print each value on a second line
+    for (String string : myList) {
+      System.out.println(string + "\n");
+    }
 
     /*
      * Usage tip!

src/MapPractice.java

@@ -1,28 +1,47 @@
-
+import java.util.HashMap;
+import java.util.Map;
 
 public class MapPractice {
   public static void main(String[] args) {
     // Create a HashMap with String keys and Integer values and
     // assign it to a variable of type Map
+    HashMap<String, Integer> map = new HashMap<>();
 
     // Put 3 different key/value pairs in the Map
     // (it's OK to do this one-by-one)
+    map.put("Red", 0);
+    map.put("Green", 1);
+    map.put("Blue", 2);
 
     // Get the value associated with a given key in the Map
+    System.out.println(map.get("Green"));
 
     // Find the size (number of key/value pairs) of the Map
+    System.out.println(map.size());
 
-    // Replace the value associated with a given key (the size of the Map shoukld not change)
+    // Replace the value associated with a given key (the size of the Map should not change)
+    map.put("Red", -1);
 
     // Check whether the Map contains a given key
+    System.out.println(map.containsKey("Yellow"));
 
     // Check whether the Map contains a given value
+    System.out.println(map.containsValue(2));
 
     // Iterate over the keys of the Map, printing each key
+    for (String key : map.keySet()) {
+      System.out.println(key);
+    }
 
     // Iterate over the values of the map, printing each value
+    for (Integer value : map.values()) {
+      System.out.println(value);
+    }
 
     // Iterate over the entries in the map, printing each key and value
+    for (Map.Entry<String, Integer> entry : map.entrySet()) {
+      System.out.println("key: " + entry.getKey() + " - value: " + entry.getValue());
+    }
 
     /*
      * Usage tip!

src/NumberPractice.java

@@ -1,17 +1,30 @@
 public class NumberPractice {
   public static void main(String args[]) {
     // Create a float with a negative value and assign it to a variable
+    double negative = -1.2;
+    System.out.println(negative);
 
     // Create an int with a positive value and assign it to a variable
+    int positive = 2;
+    System.out.println(positive);
 
     // Use the modulo % operator to find the remainder when the int is divided by 3
+    double modulo = 7 % 3;
+    System.out.println("Remainder is " + modulo);
 
     // Use the modulo % operator to determine whether the number is even
     // (A number is even if it has a remainder of zero when divided by 2)
     // Use an if-else to print "Even" if the number is even and "Odd"
     // if the number is odd.
+    int num = 4;
+    if (num % 2 == 0) {
+      System.out.println("Even");
+    } else {
+      System.out.println("Odd");
+    }
 
     // Divide the number by another number using integer division
+    System.out.println(num / positive);
 
     /*
      * Reminder!

src/Person.java

@@ -6,14 +6,21 @@
 public class Person {
   // Declare a public String instance variable for the name of the person
   // Declare a private int instance variable for the age of the person
-
+  public String name;
+  private int age;
 
   // Create a constructor that takes the name and age of the person
   // and assigns it to the instance variables
-
+  public Person(String name, int age) {
+    this.name = name;
+    this.age = age;
+  }
 
   // Create a toString method that gives the name and age of the person
-
+  @Override
+  public String toString() {
+    return name + " - " + age;
+  }
 
   // Implement the below public instance method "birthYear"
   // There should NOT be any print statement in this method.
@@ -28,26 +35,36 @@ public class Person {
    * @return The year the person was born
    */
   // (create the instance method here)
-
+  public int birthYear(int age, int currentYear) {
+    return currentYear - age;
+  }
 
   public static void main(String[] args) {
     // Create an instance of Person
+    Person me = new Person("Huma", 22);
 
     // Create another instance of Person with a different name and age and
     // assign it to a different variable
+    Person dude = new Person("The Dude", 20);
 
     // Print the first person
+    System.out.println(me);
 
     // Print the second person
+    System.out.println(dude);
 
     // Get the name of the first person and store it in a local variable
+    String name = me.name;
+    System.out.println(name);
 
     // Using the birthYear method, get the birth year of the first person
     // and store it in a local variable. Input the actual current year (e.g. 2025)
     // as the argument.
+    int birthYear = dude.birthYear(20, 2025);
 
     // In a separate statement, print the local variable holding the birth year.
-
+    System.out.println(birthYear);
+
     /**
      * Terminology!
      * 

src/SetPractice.java

@@ -1,17 +1,29 @@
+import java.util.HashSet;
+
 public class SetPractice {
   public static void main(String[] args) {
     // Create a HashSet of Strings and assign it to a variable of type Set
+    HashSet<String> set = new HashSet<>();
 
     // Add 3 elements to the set
     // (It's OK to do it one-by-one)
+    set.add("Cat");
+    set.add("Dog");
+    set.add("Bird");
 
     // Check whether the Set contains a given String
+    System.out.println(set.contains("Cat"));
 
     // Remove an element from the Set
+    set.remove("Bird");
 
     // Get the size of the Set
+    System.out.println(set.size());
 
     // Iterate over the elements of the Set, printing each one on a separate line
+    for (String string : set) {
+      System.out.println(string);
+    }
 
     /*
      * Warning!

src/StringPractice.java

@@ -1,25 +1,44 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+
 public class StringPractice {
   public static void main(String[] args) {
     // Create a string with at least 5 characters and assign it to a variable
+    String name = "Luke";
 
     // Find the length of the string
+    System.out.println(name.length());
 
     // Concatenate (add) two strings together and reassign the result
+    name += " Skywalker";
+    System.out.println(name);
 
     // Find the value of the character at index 3
+    System.out.println(name.charAt(3));
 
     // Check whether the string contains a given substring (i.e. does the string have "abc" in it?)
+    System.out.println(name.contains("Sky"));
 
     // Iterate over the characters of the string, printing each one on a separate line
+    for (int i = 0; i < name.length(); i++) {
+      System.out.println(name.charAt(i));
+    }
 
     // Create an ArrayList of Strings and assign it to a variable
-
+    ArrayList<String> list = new ArrayList<>(Arrays.asList("Strawberry", "Banana", "Grape"));
+
     // Add multiple strings to the List (OK to do one-by-one)
+    list.add("Pineapple");
 
     // Join all of the strings in the list together into a single string separated by commas
     // Use a built-in method to achieve this instead of using a loop
+    String result = String.join(", ", list);
+    System.out.println(result);
 
     // Check whether two strings are equal
+    String a = "Lol";
+    String b = "Lolo";
+    System.out.println(a == b);
 
     /*
      * Reminder!

toRefresh.md

@@ -2,4 +2,5 @@
 
 As you work through this exercise, write down anything that you needed to look up or struggled to remember here. It can be just a word or two (e.g. "joining strings"). You can use this as a guide of what to make extra sure you're refreshed on before exams and interviews.
 
-- 
+- Join strings  -->  String result = String.join(", ", list);
+- Sorting lists -->  Collections.sort(myList);