Completed all Java practice files

src/ArrayPractice.java

@@ -1,18 +1,29 @@
 public class ArrayPractice {
   public static void main(String[] args) {
     // Create an array of Strings of size 4
-
+    String[] arr = new String[4];
     // Set the value of the array at each index to be a different String
     // It's OK to do this one-by-one
+    arr[0] = "Hello";
+    arr[1] = "World";
+    arr[2] = "Java";
+    arr[3] = "Arrays";
 
     // Get the value of the array at index 2
+    System.out.println("Index 2: " + arr[2]);
 
     // Get the length of the array
-
+    System.out.println("Length: " + arr.length);
     // Iterate over the array using a traditional for loop and print out each item
-
+    System.out.println("Traditional for loop:");
+    for (int i = 0; i < arr.length; i++) {
+      System.out.println(arr[i]);
+    }
     // Iterate over the array using a for-each loop and print out each item
-
+    System.out.println("For-each loop:");
+    for (String s : arr) {
+      System.out.println(s);
+    }
     /*
      * Reminder!
      * 

src/ListPractice.java

@@ -1,35 +1,52 @@
-public class ListPractice {
+import java.util.Collections;
+import java.util.List;
+import java.util.ArrayList;
 
+public class ListPractice {
 
   public static void main(String[] args) {
     // Create an empty ArrayList of Strings and assign it to a variable of type List
+    List<String> list = new ArrayList<>();
 
     // Add 3 elements to the list (OK to do one-by-one)
-
+    list.add("Apple");
+    list.add("Banana");
+    list.add("Cherry");
     // Print the element at index 1
+    System.out.println("Index 1: " + list.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)
-
+    list.set(1, "Blueberry");
     // Insert a new element at index 0 (the length of the list will change)
-
+    list.add(0, "Date");
     // Check whether the list contains a certain string
-
+    System.out.println("Contains Apple? " + list.contains("Apple"));
     // Iterate over the list using a traditional for-loop.
     // Print each index and value on a separate line
-
+    for (int i = 0; i < list.size(); i++) {
+      System.out.println(i + ": " + list.get(i));
+    }
     // Sort the list using the Collections library
-
+    Collections.sort(list);
     // Iterate over the list using a for-each loop
+    for (String item : list) {
+      System.out.println(item);
+    }
     // Print each value on a second line
+    for (String item : list) {
+      System.out.println(item);
+    }
 
     /*
      * Usage tip!
      * 
-     * Use a traditional for-loop when you need to use the index or you need to iterate in an
+     * Use a traditional for-loop when you need to use the index or you need to
+     * iterate in an
      * unconventional order (e.g. backwards)
      * 
-     * Otherwise, if you're iterating the in the conventional order and don't need the
+     * Otherwise, if you're iterating the in the conventional order and don't need
+     * the
      * index values a for-each loop is cleaner.
      */
   }

src/MapPractice.java

@@ -1,40 +1,56 @@
-
+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
-
+    Map<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("Apples", 5);
+    map.put("Bananas", 10);
+    map.put("Cherries", 15);
     // Get the value associated with a given key in the Map
-
+    System.out.println("Value for 'Bananas': " + map.get("Bananas"));
     // Find the size (number of key/value pairs) of the Map
-
-    // Replace the value associated with a given key (the size of the Map shoukld not change)
-
+    System.out.println("Map size: " + map.size());
+    // Replace the value associated with a given key (the size of the Map shoukld
+    // not change)
+    map.put("Bananas", 12);
+    System.out.println("Updated value for 'Bananas': " + map.get("Bananas"));
     // Check whether the Map contains a given key
-
+    System.out.println("Contains key 'Apples'? " + map.containsKey("Apples"));
     // Check whether the Map contains a given value
-
+    System.out.println("Contains value 15? " + map.containsValue(15));
     // Iterate over the keys of the Map, printing each key
-
+    System.out.println("Keys in map:");
+    for (String key : map.keySet()) {
+      System.out.println(key);
+    }
     // Iterate over the values of the map, printing each value
-
+    System.out.println("Values in map:");
+    for (Integer value : map.values()) {
+      System.out.println(value);
+    }
     // Iterate over the entries in the map, printing each key and value
-
+    System.out.println("Entries in map:");
+    for (Map.Entry<String, Integer> entry : map.entrySet()) {
+      System.out.println(entry.getKey() + " -> " + entry.getValue());
+    }
     /*
      * Usage tip!
      * 
      * Maps are great when you want a specific key to value mapping.
-     * Example: The key could be a person's name, and the value could be their phone number
+     * Example: The key could be a person's name, and the value could be their phone
+     * number
      * 
      * However if your keys are simple ascending 0-indexed integers with no gaps
      * (0, 1, 2, 3, 4...) then an array or List is likely a better choice.
      * Example: If you want to store the order of songs in a playlist.
      * 
-     * If you're finding that you're just wanting to store unordered values and the keys
+     * If you're finding that you're just wanting to store unordered values and the
+     * keys
      * are unimportant, a Set may be a better choice.
      * Example: If you want to hold the student ID numbers of everyone in a course,
      * and you don't care about any ordering.

src/NumberPractice.java

@@ -1,23 +1,31 @@
 public class NumberPractice {
   public static void main(String args[]) {
     // Create a float with a negative value and assign it to a variable
-
+    float negativeFloat = -4.5f;
+    System.out.println("Negative float: " + negativeFloat);
     // Create an int with a positive value and assign it to a variable
-
+    int positiveInt = 10;
+    System.out.println("Positive int: " + positiveInt);
     // Use the modulo % operator to find the remainder when the int is divided by 3
-
+    int remainder = positiveInt % 3;
+    System.out.println("Remainder of " + positiveInt + " % 3 = " + remainder);
     // 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.
-
+    if (positiveInt % 2 == 0) {
+      System.out.println(positiveInt + " is even");
+    } else {
+      System.out.println(positiveInt + " is odd");
+    }
     // Divide the number by another number using integer division
-
+    int divided = positiveInt / 4;
+    System.out.println(positiveInt + " / 4 = " + divided);
     /*
      * Reminder!
      * 
      * When dividing ints, the result is rounded down.
-     * Example: 
+     * Example:
      * 7 / 3 = 2 when performing int division
      */
 

src/Person.java

@@ -5,15 +5,22 @@
 
 public class Person {
   // Declare a public String instance variable for the name of the person
+  public String name;
   // Declare a private int instance variable for the age of the person
-
+  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 "Person{name='" + name + "', age=" + age + "}";
+  }
 
   // Implement the below public instance method "birthYear"
   // There should NOT be any print statement in this method.
@@ -28,39 +35,44 @@ public class Person {
    * @return The year the person was born
    */
   // (create the instance method here)
-
+  public int birthYear(int currentYear) {
+    return currentYear - age;
+  }
 
   public static void main(String[] args) {
     // Create an instance of Person
-
+    Person person1 = new Person("Alice", 25);
     // Create another instance of Person with a different name and age and
     // assign it to a different variable
-
+    Person person2 = new Person("Bob", 30);
     // Print the first person
-
+    System.out.println(person1);
     // Print the second person
-
+    System.out.println(person2);
     // Get the name of the first person and store it in a local variable
-
+    String firstName = person1.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 = person1.birthYear(2025);
     // In a separate statement, print the local variable holding the birth year.
-
+    System.out.println(firstName + " was born in " + birthYear);
     /**
      * Terminology!
      * 
      * A class is the overall definition, like a blueprint.
      * An instance is a specific object made according to that definition.
      * We use "instance" and "object" to mean the same thing.
      * 
-     * For example, if there is a Person class, we can make an instance of a specific person: Auberon.
+     * For example, if there is a Person class, we can make an instance of a
+     * specific person: Auberon.
      * 
-     * There can be many instances for the same class. For example: Auberon, Xinting, Baya are all
+     * There can be many instances for the same class. For example: Auberon,
+     * Xinting, Baya are all
      * different instances of the Person class.
      * 
-     * Each instance has its own instance variables: Auberon's age can be different from Baya's age.
+     * Each instance has its own instance variables: Auberon's age can be different
+     * from Baya's age.
      */
   }
 }

src/SetPractice.java

@@ -1,26 +1,37 @@
+import java.util.Set;
+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
-
+    Set<String> set = new HashSet<>();
     // Add 3 elements to the set
     // (It's OK to do it one-by-one)
-
+    set.add("Apple");
+    set.add("Banana");
+    set.add("Cherry");
     // Check whether the Set contains a given String
-
+    System.out.println("Contains 'Banana'? " + set.contains("Banana"));
     // Remove an element from the Set
-
+    set.remove("Apple");
+    System.out.println("Removed 'Apple'");
     // Get the size of the Set
-
+    System.out.println("Set size: " + set.size());
     // Iterate over the elements of the Set, printing each one on a separate line
-
+    System.out.println("Elements in set:");
+    for (String item : set) {
+      System.out.println(item);
+    }
     /*
      * Warning!
      * 
      * The iteration order over the items in a HashSet is NOT GUARANTEED.
      * 
-     * Even running the exact same program multiple times may give different results.
+     * Even running the exact same program multiple times may give different
+     * results.
      * Do not use a HashSet if order is important! You can use a TreeSet if you
-     * want items in sorted order, or an array or List if you want them in a specified
+     * want items in sorted order, or an array or List if you want them in a
+     * specified
      * order.
      * 
      * Also remember that sets do NOT have duplicates.

src/StringPractice.java

@@ -1,26 +1,42 @@
+import java.util.ArrayList;
+import java.util.List;
+
 public class StringPractice {
   public static void main(String[] args) {
     // Create a string with at least 5 characters and assign it to a variable
-
+    String text = "HelloWorld";
     // Find the length of the string
-
+    System.out.println("Length: " + text.length());
     // Concatenate (add) two strings together and reassign the result
-
+    text = text + "123";
+    System.out.println("After concatenation: " + text);
     // Find the value of the character at index 3
-
-    // Check whether the string contains a given substring (i.e. does the string have "abc" in it?)
-
-    // Iterate over the characters of the string, printing each one on a separate line
-
+    System.out.println("Character at index 3: " + text.charAt(3));
+    // Check whether the string contains a given substring (i.e. does the string
+    // have "abc" in it?)
+    System.out.println("Contains 'abc'? " + text.contains("abc"));
+    // Iterate over the characters of the string, printing each one on a separate
+    // line
+    System.out.println("Characters in the string:");
+    for (int i = 0; i < text.length(); i++) {
+      System.out.println(text.charAt(i));
+    }
     // Create an ArrayList of Strings and assign it to a variable
-
+    List<String> words = new ArrayList<>();
     // Add multiple strings to the List (OK to do one-by-one)
-
-    // Join all of the strings in the list together into a single string separated by commas
+    words.add("Apple");
+    words.add("Banana");
+    words.add("Cherry");
+    // 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 joined = String.join(", ", words);
+    System.out.println("Joined list: " + joined);
     // Check whether two strings are equal
-
+    String s1 = "Hello";
+    String s2 = "hello";
+    System.out.println("s1 equals s2? " + s1.equals(s2));
+    System.out.println("s1 equalsIgnoreCase s2? " + s1.equalsIgnoreCase(s2));
     /*
      * Reminder!
      *