Java Derusting

src/ArrayPractice.java

@@ -1,22 +1,37 @@
 public class ArrayPractice {
   public static void main(String[] args) {
     // Create an array of Strings of size 4
+    String[] arrayFour = 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
+    arrayFour[0] = "ZERO";
+    arrayFour[1] = "ONE";
+    arrayFour[2] = "TWO";
+    arrayFour[3] = "THREE";
 
     // Get the value of the array at index 2
+    System.out.println(arrayFour[2]); //output: TWO
 
     // Get the length of the array
+    System.out.println(arrayFour.length);
 
     // Iterate over the array using a traditional for loop and print out each item
+    for (int i = 0; i < arrayFour.length; i++) {
+      System.out.println(arrayFour[i]);
+    }
 
     // Iterate over the array using a for-each loop and print out each item
+    for (String string : arrayFour) {
+      System.out.println(string);
+    }
 
     /*
      * Reminder!
      * 
      * Arrays start at index 0
      */
+
+     //DONE
   }
 }

src/ListPractice.java

@@ -1,27 +1,49 @@
+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> stringList = new ArrayList<>();
 
     // Add 3 elements to the list (OK to do one-by-one)
+      stringList.add("APPLE");
+      stringList.add("BANANA");
+      stringList.add("KIWI");
 
     // Print the element at index 1
-
+      System.out.println(stringList.get(1)); //output: BANANA
+
     // Replace the element at index 1 with a new value
     // (Do not insert a new value. The length of the list should not change)
+      stringList.set(1, "STRAWBERRY");
 
     // Insert a new element at index 0 (the length of the list will change)
+      stringList.add(0, "ORANGE");
 
     // Check whether the list contains a certain string
+      if (stringList.contains("AVOCADO")) {
+        System.out.println("We have avocado :)");
+      } else {
+        System.out.println("There is no avocado :(");
+      }
 
     // Iterate over the list using a traditional for-loop.
     // Print each index and value on a separate line
+      for (int i = 0; i < stringList.size(); i++) {
+        System.out.println(i + ": " + stringList.get(i));
+      }
 
     // Sort the list using the Collections library
+      Collections.sort(stringList);
 
     // Iterate over the list using a for-each loop
     // Print each value on a second line
+      for (String fruit : stringList) {
+        System.out.println(fruit);
+      }
 
     /*
      * Usage tip!
@@ -32,5 +54,7 @@ public static void main(String[] args) {
      * Otherwise, if you're iterating the in the conventional order and don't need the
      * index values a for-each loop is cleaner.
      */
+
+     //DONE
   }
 }

src/MapPractice.java

@@ -1,28 +1,55 @@
-
+import java.util.HashMap;
 
 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> mappy = new HashMap<>();
     // Put 3 different key/value pairs in the Map
     // (it's OK to do this one-by-one)
+      mappy.put("a", 1);
+      mappy.put("b", 2);
+      mappy.put("c", 3);
 
     // Get the value associated with a given key in the Map
+    mappy.get("a");
 
     // Find the size (number of key/value pairs) of the Map
+    mappy.size();
 
     // Replace the value associated with a given key (the size of the Map shoukld not change)
+    mappy.replace("a", 0);
 
     // Check whether the Map contains a given key
+    if (mappy.containsKey("d")) {
+      System.out.println("Letter d, is present within list MAPPY");
+    } else {
+      System.out.println("There is no key present");
+    }
 
     // Check whether the Map contains a given value
+    if (mappy.containsValue(2)) {
+      System.out.println("Value 2, is present within list MAPPY");
+    } else {
+      System.out.println("There is no value present");
+    }
 
     // Iterate over the keys of the Map, printing each key
+    for (String key : mappy.keySet()) {
+      System.out.println(key);
+    }
 
     // Iterate over the values of the map, printing each value
+    for (Integer value : mappy.values()) {
+      System.out.println(value);
+    }
 
     // Iterate over the entries in the map, printing each key and value
+    for (HashMap.Entry<String, Integer> entries : mappy.entrySet()) {
+      System.out.println("KEY " + entries.getKey());
+      System.out.println("VALUE " + entries.getValue());
+    }
 
     /*
      * Usage tip!
@@ -39,5 +66,7 @@ public static void main(String[] args) {
      * Example: If you want to hold the student ID numbers of everyone in a course,
      * and you don't care about any ordering.
      */
+
+    //DONE
   }
 }

src/NumberPractice.java

@@ -1,17 +1,27 @@
 public class NumberPractice {
   public static void main(String args[]) {
     // Create a float with a negative value and assign it to a variable
+    float negativeVal = -123f;
 
     // Create an int with a positive value and assign it to a variable
+    int positiveVal = 123;
 
     // Use the modulo % operator to find the remainder when the int is divided by 3
+    int remainder = positiveVal % 3;
 
     // 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 (positiveVal % 2 == 0) {
+      System.out.println("EVEN");
+    } else {
+      System.out.println("ODD");
+    }
 
     // Divide the number by another number using integer division
+    int division = positiveVal / 3;
+    System.out.println(division);
 
     /*
      * Reminder!
@@ -20,6 +30,6 @@ public static void main(String args[]) {
      * Example: 
      * 7 / 3 = 2 when performing int division
      */
-
+    //DONE
   }
 }

src/Person.java

@@ -6,14 +6,20 @@
 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 + ", Age: " + age;
+  }
 
   // Implement the below public instance method "birthYear"
   // There should NOT be any print statement in this method.
@@ -28,25 +34,35 @@ 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 personOne = new Person("Caitlyn Kiramman", 24);
 
     // Create another instance of Person with a different name and age and
     // assign it to a different variable
-
+    Person personTwo = new Person("Mel Medarda", 33);
+
     // Print the first person
+    System.out.println(personOne);
 
     // Print the second person
+    System.out.println(personTwo);
 
     // Get the name of the first person and store it in a local variable
+    String ArcaneChara1 = personOne.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 currentYear = 2025;
+    int birthYear1 = personOne.birthYear(currentYear);
 
     // In a separate statement, print the local variable holding the birth year.
+    System.out.println(personOne.name + "Birth Year: " + birthYear1); 
 
     /**
      * Terminology!
@@ -62,5 +78,7 @@ public static void main(String[] args) {
      * 
      * Each instance has its own instance variables: Auberon's age can be different from Baya's age.
      */
+
+     //DONE
   }
 }

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> StringSet = new HashSet<>();
 
     // Add 3 elements to the set
     // (It's OK to do it one-by-one)
+      StringSet.add("TOMATO");
+      StringSet.add("POTATO");
+      StringSet.add("YAM");
 
     // Check whether the Set contains a given String
+      StringSet.contains("CABBAGE");
 
     // Remove an element from the Set
+      StringSet.remove("TOMATO");
 
     // Get the size of the Set
+      StringSet.size();
 
     // Iterate over the elements of the Set, printing each one on a separate line
+    for (String veggie : StringSet) {
+        System.out.println(veggie);
+    }
 
     /*
      * Warning!
@@ -25,5 +37,7 @@ public static void main(String[] args) {
      * 
      * Also remember that sets do NOT have duplicates.
      */
+
+     //DONE
   }
 }

src/StringPractice.java

@@ -1,25 +1,52 @@
+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 name = "Luigi";
+    System.out.println(name);
 
     // Find the length of the string
+    System.out.println(name.length());
+    System.out.println();
 
     // Concatenate (add) two strings together and reassign the result
+    String nameTwo = "Mario ";
+    String result = nameTwo + name;
+    System.out.println(result);
 
     // 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?)
+    boolean substring = name.contains("abc");
+    System.out.println(substring);
 
     // Iterate over the characters of the string, printing each one on a separate line
+    for (char letter : name.toCharArray()) {
+      System.out.println(letter);
+    }
 
     // Create an ArrayList of Strings and assign it to a variable
-
+    ArrayList<String> Spiders = new ArrayList<>();
     // Add multiple strings to the List (OK to do one-by-one)
+        Spiders.add("Peter Parker");
+        Spiders.add("Miguel O'Hara");
+        Spiders.add("Miles Morales");
+        Spiders.add("Gwen Stacy");
+        Spiders.add("Peni Parker");
 
     // 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 SpiderPeople = String.join(", ", Spiders);
+    System.out.println(SpiderPeople);
+
     // Check whether two strings are equal
+    if (Spiders.get(3).equals(4)) {
+      System.out.println("Their names are equal!");
+    } else {
+      System.out.println("Their names are not equal");
+    }
 
     /*
      * Reminder!
@@ -28,5 +55,7 @@ public static void main(String[] args) {
      * 
      * We use == when comparing primitives (e.g. int or char).
      */
+
+     //DONE 
   }
 }

toRefresh.md

@@ -2,4 +2,13 @@
 
 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.
 
-- 
+- ArrayList 
+- Map Entries
+- Set vs. Map
+- Float
+- .toCharArray()
+
+- Public Private
+- Constructor
+- toString
+- Instance