De-rusting Java PR - Jaron

src/ArrayPractice.java

@@ -1,18 +1,32 @@
+  import java.util.Arrays;
 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] = "This";
+    arr[1] = "is";
+    arr[2] = "an";
+    arr[3] = "array";
 
     // Get the value of the array at index 2
+    String valueAtIndex2 = arr[2]; // Receiving the value at index 2
 
     // Get the length of the array
+    int lengthOfArray = arr.length; // Length of array
 
     // Iterate over the array using a traditional for loop and print out each item
+    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
-
+    for(String item : arr){
+      System.out.println(item);
+    }
     /*
      * Reminder!
      * 

src/ListPractice.java

@@ -1,27 +1,46 @@
+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("First");
+    myList.add("Second");
+    myList.add("Third");
 
     // Print the element at index 1
+    System.out.println(myList.get(1)); // Getting the element at index 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, "replaced value"); // Replacing the element at index 1 with .set()
 
     // Insert a new element at index 0 (the length of the list will change)
+    myList.add(0, "new value here"); // Inserting a new element
 
     // Check whether the list contains a certain string
+    boolean containsString = myList.contains("First"); // Checking if the list contains "First"
+    System.out.println("List contains a string: " + containsString);
 
     // 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("Index: " + i + "\n" + "Value: " + myList.get(i));
+    }
 
     // Sort the list using the Collections library
+    Collections.sort(myList); // Sorting the list
 
     // Iterate over the list using a for-each loop
     // Print each value on a second line
+    for(String item : myList){
+      System.out.println(item);
+    }
 
     /*
      * Usage tip!

src/MapPractice.java

@@ -1,28 +1,50 @@
 
+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> myMap = new HashMap<>();
+
 
     // Put 3 different key/value pairs in the Map
     // (it's OK to do this one-by-one)
+    myMap.put("First", 1);
+    myMap.put("Second", 2);
+    myMap.put("Third", 3);
 
     // Get the value associated with a given key in the Map
+    int valueForKey = myMap.get("Second"); // Getting the value for the key "Second"
 
     // Find the size (number of key/value pairs) of the Map
+    int mapSize = myMap.size(); // Size of the map
 
     // Replace the value associated with a given key (the size of the Map shoukld not change)
+    myMap.put("Second", 22); // Replacing the value for the key "Second"
 
     // Check whether the Map contains a given key
+    boolean containsKey = myMap.containsKey("First");
+    System.out.println("Map contains key: " + containsKey);
 
     // Check whether the Map contains a given value
+    boolean containsValue = myMap.containsValue(3);
+    System.out.println("Map contains value: " + containsValue);
 
     // Iterate over the keys of the Map, printing each key
-
+    for(String key : myMap.keySet()){ // using keySet() to grab all keys
+      System.out.println(key);
+    }
     // Iterate over the values of the map, printing each value
+    for(Integer value : myMap.values()) { // using values() to grab all values, with Integer type
+      System.out.println(value);
+    }
 
     // Iterate over the entries in the map, printing each key and value
+    for(Map.Entry<String, Integer> entry : myMap.entrySet()) { // using entrySet() to grab all entries with Entry type.
+      System.out.println("Key: " + entry.getKey() + "\n" + "Value: " + entry.getValue());
+    }
 
     /*
      * Usage tip!

src/NumberPractice.java

@@ -1,17 +1,28 @@
 public class NumberPractice {
   public static void main(String args[]) {
     // Create a float with a negative value and assign it to a variable
+    float negativeFloat = -3.14f; // Creating a float with a negative value
 
     // Create an int with a positive value and assign it to a variable
+    int posInt = 42; // Creating an int with a positive value
 
     // Use the modulo % operator to find the remainder when the int is divided by 3
+    int remainder = posInt % 3; // Remainder given 3 as the divisor
+    System.out.println(remainder); // printing 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(posInt % 2 == 0){
+      System.out.println("Even");
+    } else {
+      System.out.println("Odd");
+    }
 
     // Divide the number by another number using integer division
+    int divisionResult = posInt / 5; // Integer division
+    System.out.println(divisionResult); // printing result of integer division
 
     /*
      * Reminder!

src/Person.java

@@ -6,13 +6,22 @@
 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
+  public String toString(){
+    return "Name: " + name + "\n" + "Age: " + age;
+  }
 
 
   // Implement the below public instance method "birthYear"
@@ -28,25 +37,36 @@ public class Person {
    * @return The year the person was born
    */
   // (create the instance method here)
+  public int birthYear(int year){
+    int birthYear = year - age;
+    return birthYear;
+  }
 
 
   public static void main(String[] args) {
     // Create an instance of Person
+    Person person1 = new Person("Jaron", 19); // creating new instance of Person object
 
     // Create another instance of Person with a different name and age and
     // assign it to a different variable
+    Person person2 = new Person("Maxwell", 10); // creating another instance of Person object
 
     // 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 name1 = 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("Birth year of " + name1 + ": " + birthYear);
 
     /**
      * Terminology!

src/SetPractice.java

@@ -1,17 +1,31 @@
+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> mySet = new HashSet<>();
+
 
     // Add 3 elements to the set
     // (It's OK to do it one-by-one)
+    mySet.add("First");
+    mySet.add("Second");
+    mySet.add("Third");
 
     // Check whether the Set contains a given String
+    boolean containsString = mySet.contains("Second"); // checking if a given string exists in set
+    System.out.println("Set contains string: " + containsString);
 
     // Remove an element from the Set
+    mySet.remove("Second");
 
     // Get the size of the Set
+    int setSize = mySet.size(); // size of the set
 
     // Iterate over the elements of the Set, printing each one on a separate line
+    for(String item : mySet){ // using for-each loop to iterate over the set
+      System.out.println(item);
+    }
 
     /*
      * Warning!

src/StringPractice.java

@@ -1,25 +1,46 @@
-public class StringPractice {
+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 fiveLetterString = "Hello";
 
     // Find the length of the string
+    fiveLetterString.length();
+
 
     // Concatenate (add) two strings together and reassign the result
+    String newString = fiveLetterString + "World"; // Concatenating two strings together
 
     // Find the value of the character at index 3
+    char charAtIndex3 = fiveLetterString.charAt(3); // Getting the character at index 3
 
     // Check whether the string contains a given substring (i.e. does the string have "abc" in it?)
+    boolean checkSubstring = fiveLetterString.contains("llo");
 
     // Iterate over the characters of the string, printing each one on a separate line
+    for(int i = 0; i < fiveLetterString.length(); i++){
+      System.out.println(fiveLetterString.charAt(i)); // using charAt to print each index
+    }
 
     // Create an ArrayList of Strings and assign it to a variable
+    ArrayList<String> myArrayList = new ArrayList<>();
 
     // Add multiple strings to the List (OK to do one-by-one)
+    myArrayList.add("First");
+    myArrayList.add("Second");
+    myArrayList.add("Third");
 
     // 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 joinedString = String.join(",", myArrayList); // Joining the strings in the list together with commas using .join();
 
     // Check whether two strings are equal
+    String string1 = "Hello";
+    String string2 = "world";
+
+    boolean stringsEqual = string1.equals(string2); // Checking if two strings are equal with .equals()
 
     /*
      * Reminder!