Added java code

src/ArrayPractice.java

@@ -1,18 +1,39 @@
 public class ArrayPractice {
   public static void main(String[] args) {
-    // Create an array of Strings of size 4
+    String[] fruits = new String[4];
+
+// Set the value of the array at each index to be a different String
 
-    // Set the value of the array at each index to be a different String
     // It's OK to do this one-by-one
+    fruits[0] = "Orange"
+    fruits[1] = "Pear"
+    fruits[2] = "Banana"
+    fruits[3] = "Cherry"
+
+
 
     // Get the value of the array at index 2
+    String valueAtIndex2 = fruits[2];
+    System.out.println("Value at index 2: " + valueAtIndex2);
 
     // Get the length of the array
+    int arrayLength = fruits.length;
+    System.out.println("Array length: " + arrayLength);
+
 
     // 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 < fruits.length; i++) {
+        System.out.println(fruits[i]);
+    }
+
     // Iterate over the array using a for-each loop and print out each item
 
+     System.out.println("For-each loop:");
+      for (String fruit : fruits) {
+      System.out.println(fruit);
+    }
     /*
      * Reminder!
      * 

src/ListPractice.java

@@ -1,25 +1,53 @@
-public class ListPractice {
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
 
+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> animals = new ArrayList<>();
 
     // Add 3 elements to the list (OK to do one-by-one)
+        animals.add("Dog");
+        animals.add("Cat");
+        animals.add("Rabbit");
 
     // Print the element at index 1
+    System.out.println("Element at index 1: " + animals.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)
+    animals.set(1, "Lion");
 
+    // (Do not insert a new value. The length of the list should not change)
     // Insert a new element at index 0 (the length of the list will change)
+    animals.add(0, "Elephant");
 
     // Check whether the list contains a certain string
+       if (animals.contains("Rabbit")) {
+          System.out.println("The list contains 'Rabbit'.");
+      } else {
+          System.out.println("The list does not contain 'Rabbit'.");
+    }
 
     // Iterate over the list using a traditional for-loop.
     // Print each index and value on a separate line
 
+      System.out.println("Using traditional for loop:");
+      for (int i = 0; i < animals.size(); i++) {
+        System.out.println("Index " + i + ": " + animals.get(i));
+    }
+
     // Sort the list using the Collections library
 
+    Collections.sort(animals);
+
+    System.out.println("For-each loop after sorting:");
+    for (String animal : animals) {
+      System.out.println(animal);
+    }
+
     // Iterate over the list using a for-each loop
     // Print each value on a second line
 

src/MapPractice.java

@@ -1,28 +1,53 @@
-
+import java.util.*;
 
 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> scores = new HashMap<>();
 
     // Put 3 different key/value pairs in the Map
     // (it's OK to do this one-by-one)
+    scores.put("Alice", 85);
+    scores.put("Bob", 90);
+    scores.put("Charlie", 78);
 
     // Get the value associated with a given key in the Map
+    System.out.println("Score for Bob: " + scores.get("Bob"));
 
     // Find the size (number of key/value pairs) of the Map
+    System.out.println("Size of the map: " + scores.size());
 
     // Replace the value associated with a given key (the size of the Map shoukld not change)
+    scores.put("Alice", 95);
 
     // Check whether the Map contains a given key
+    if (scores.containsKey("Charlie")) {
+      System.out.println("The map contains the key 'Charlie'.");
+    }
 
     // Check whether the Map contains a given value
+    if (scores.containsValue(90)) {
+      System.out.println("The map contains the value 90.");
+    }
 
     // Iterate over the keys of the Map, printing each key
+    System.out.println("Keys in the map:");
+    for (String key : scores.keySet()) {
+      System.out.println(key);
+    }
 
     // Iterate over the values of the map, printing each value
+    System.out.println("Values in the map:");
+    for (Integer value : scores.values()) {
+      System.out.println(value);
+    }
 
     // Iterate over the entries in the map, printing each key and value
+    System.out.println("Entries in the map:");
+    for (Map.Entry<String, Integer> entry : scores.entrySet()) {
+      System.out.println(entry.getKey() + ": " + entry.getValue());
+    }
 
     /*
      * Usage tip!

src/NumberPractice.java

@@ -1,17 +1,29 @@
 public class NumberPractice {
   public static void main(String args[]) {
     // Create a float with a negative value and assign it to a variable
+    float negativeFloat = -5.75f;
 
     // Create an int with a positive value and assign it to a variable
+    int positiveInt = 14;
 
     // Use the modulo % operator to find the remainder when the int is divided by 3
+    int remainder = positiveInt % 3;
+    System.out.println("Remainder when divided by 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("Even");
+    } else {
+      System.out.println("Odd");
+    }
+
     // Divide the number by another number using integer division
+    int result = positiveInt / 4;
+      System.out.println("Result of integer division: " + result);
 
     /*
      * Reminder!

src/Person.java

@@ -5,18 +5,33 @@
 
 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.
+  public int birthYear(int currentYear) {
+    return currentYear - age;
+  }
+
   /**
    * birthYear returns the year the person was born.
    * 
@@ -32,21 +47,28 @@ public class Person {
 
   public static void main(String[] args) {
     // Create an instance of Person
+    Person person1 = new Person("Auberon", 25);
 
     // Create another instance of Person with a different name and age and
     // assign it to a different variable
+    Person person2 = new Person("Xinting", 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 birthYear1 = person1.birthYear(2025);
 
     // In a separate statement, print the local variable holding the birth year.
+    System.out.println("Birth year of " + firstName + ": " + birthYear1);
 
     /**
      * Terminology!

src/SetPractice.java

@@ -1,17 +1,37 @@
+import java.util.HashSet;
+import java.util.Set;
+
+
+
 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> fruits = new HashSet<>();
 
     // Add 3 elements to the set
     // (It's OK to do it one-by-one)
+    fruits.add("Apple");
+    fruits.add("Banana");
+    fruits.add("Cherry");
 
     // Check whether the Set contains a given String
+     if (fruits.contains("Banana")) {
+      System.out.println("The set contains 'Banana'.");
+    } else {
+      System.out.println("The set does not contain 'Banana'.");
+    }
 
     // Remove an element from the Set
+    fruits.remove("Cherry");
 
     // Get the size of the Set
+    System.out.println("Size of the set: " + fruits.size());
 
     // Iterate over the elements of the Set, printing each one on a separate line
+    System.out.println("Elements in the set:");
+    for (String fruit : fruits) {
+      System.out.println(fruit);
+    }
 
     /*
      * Warning!

src/StringPractice.java

@@ -1,25 +1,50 @@
+import java.util.ArrayList;
+
 public class StringPractice {
   public static void main(String[] args) {
     // Create a string with at least 5 characters and assign it to a variable
+    String message = "Hello";
 
     // Find the length of the string
+    int length = message.length();
+    System.out.println("Length of the string: " + length);
 
     // Concatenate (add) two strings together and reassign the result
+    message += " World!";
+    System.out.println("Concatenated string: " + message);
 
     // Find the value of the character at index 3
+    char charAtIndex3 = message.charAt(3);
+    System.out.println("Character at index 3: " + charAtIndex3);
 
     // Check whether the string contains a given substring (i.e. does the string have "abc" in it?)
+    boolean containsWord = message.contains("World");
+    System.out.println("Does the string contain 'World'? " + containsWord);
 
     // Iterate over the characters of the string, printing each one on a separate line
+     System.out.println("Characters in the string:");
+     for (char ch : message.toCharArray()) {
+      System.out.println(ch);
+    }
 
     // Create an ArrayList of Strings and assign it to a variable
+    ArrayList<String> words = new ArrayList<>();
 
     // Add multiple strings to the List (OK to do one-by-one)
+    words.add("Java");
+    words.add("is");
+    words.add("awesome");
 
     // 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 joinedWords = String.join(", ", words);
+    System.out.println("Joined string: " + joinedWords);
 
     // Check whether two strings are equal
+    String str1 = "Hello";
+    String str2 = "hello";
+    boolean areEqual = str1.equalsIgnoreCase(str2);
+    System.out.println("Are the strings equal (ignoring case)? " + areEqual);
 
     /*
      * Reminder!