Java Derusting assignment

src/ArrayPractice.java

@@ -1,17 +1,35 @@
+
 public class ArrayPractice {
   public static void main(String[] args) {
     // Create an array of Strings of size 4
+    String[] array = 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
+    array[0] = "Noodles";
+    array[1] = "Rice";
+    array[2] = "Pasta";
+    array[3] = "Bread";
+    // System.out.println(array[0]);
+    // System.out.println(array[1]);
+    // System.out.println(array[2]);
+    // System.out.println(array[3]);
 
     // Get the value of the array at index 2
+    System.out.println(array[2]);
 
     // Get the length of the array
+    System.out.println(array.length);
 
     // Iterate over the array using a traditional for loop and print out each item
+    for (int i = 0; i < array.length; i++){
+      System.out.println(array[i]);
+    }
 
     // Iterate over the array using a for-each loop and print out each item
+    for (String str : array) {
+      System.out.println(str);
+    }
 
     /*
      * Reminder!

src/ListPractice.java

@@ -1,27 +1,48 @@
-public class ListPractice {
+import java.util.*;
 
+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("Hi");
+    list.add("Hello");
+    list.add("Good morning");
+    System.out.println(list);
 
     // Print the element at index 1
+    System.out.println(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,"Hey");
+    System.out.println(list);
 
     // Insert a new element at index 0 (the length of the list will change)
+    list.add(0, "Good night");
+    System.out.println(list);
 
     // Check whether the list contains a certain string
+    System.out.println(list.contains("Hey"));
 
     // 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++){
+      String word = list.get(i);
+      System.out.println("Value at index " + i + ": " + word);
+    }
 
     // Sort the list using the Collections library
+    Collections.sort(list);
+    System.out.println(list);
 
     // Iterate over the list using a for-each loop
     // Print each value on a second line
+    for (String str : list){
+      System.out.println(str);
+    }
 
     /*
      * Usage tip!

src/MapPractice.java

@@ -1,28 +1,48 @@
-
+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> dict = new HashMap<>();
 
     // Put 3 different key/value pairs in the Map
     // (it's OK to do this one-by-one)
+    dict.put("Pooh", 1);
+    dict.put("Tigger", 3);
+    dict.put("Eeyore", 6);
+    System.out.println(dict);
 
     // Get the value associated with a given key in the Map
+    System.out.println(dict.get("Eeyore"));
 
     // Find the size (number of key/value pairs) of the Map
+    System.out.println(dict.size());
 
     // Replace the value associated with a given key (the size of the Map shoukld not change)
+    dict.replace("Pooh", 9);
+    System.out.println(dict);
 
     // Check whether the Map contains a given key
+    System.out.println(dict.containsKey("Tigger"));
 
     // Check whether the Map contains a given value
+    System.out.println(dict.containsValue(9));
 
     // Iterate over the keys of the Map, printing each key
+    for (String str : dict.keySet()){
+      System.out.println(str);
+    }
 
     // Iterate over the values of the map, printing each value
+    for (int v : dict.values()){
+      System.out.println(v);
+    }
 
     // Iterate over the entries in the map, printing each key and value
+    for (String s : dict.keySet()){
+      System.out.println("Key: " + s + ", Value: " + dict.get(s));
+    }
 
     /*
      * 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 num = -2.345f;
+    System.out.println(num);
 
     // Create an int with a positive value and assign it to a variable
+    int positiveNum = 5;
+    System.out.println(positiveNum);
 
     // Use the modulo % operator to find the remainder when the int is divided by 3
+    System.out.println(positiveNum % 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 (positiveNum % 2 == 0){
+      System.out.println("Even");
+    } else {
+      System.out.println("Odd");
+    }
 
     // Divide the number by another number using integer division
+    System.out.println(positiveNum / 5);
 
     /*
      * Reminder!

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 +34,38 @@ public class Person {
    * @return The year the person was born
    */
   // (create the instance method here)
+    public int birthYear(int currentYear) {
+      int birthYear = currentYear - age;
+      return birthYear;
+    }
 
 
   public static void main(String[] args) {
     // Create an instance of Person
+    Person p1 = new Person("Harry Potter", 27);
 
     // Create another instance of Person with a different name and age and
     // assign it to a different variable
+    Person p2 = new Person("Ron Weasley", 28);
 
     // Print the first person
+    System.out.println(p1);
 
     // Print the second person
+    System.out.println(p2);
 
     // Get the name of the first person and store it in a local variable
+    String name1 = p1.name;
+    System.out.println(name1);
 
     // 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 age1 = p1.age; - don't need this
+    int birthYear1 = p1.birthYear(2025);
 
     // In a separate statement, print the local variable holding the birth year.
+    System.out.println(birthYear1);
 
     /**
      * Terminology!

src/SetPractice.java

@@ -1,17 +1,31 @@
+import java.util.*;
+
 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("Pen");
+    set.add("Pencil");
+    set.add("Eraser");
+    System.out.println(set);
 
     // Check whether the Set contains a given String
+    System.out.println(set.contains("Pen"));
 
     // Remove an element from the Set
+    System.out.println(set.remove("Eraser"));
+    System.out.println(set);
 
     // 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 str : set) {
+      System.out.println(str);
+    }
 
     /*
      * Warning!

src/StringPractice.java

@@ -1,25 +1,56 @@
+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 word = "October";
+    System.out.println(word);
 
     // Find the length of the string
+    System.out.println(word.length());
 
     // Concatenate (add) two strings together and reassign the result
-
+    String word2 = "November";
+    String newWord = word + " " + word2;
+    System.out.println(newWord);
+
     // Find the value of the character at index 3
+    System.out.println(newWord.charAt(3));
 
     // Check whether the string contains a given substring (i.e. does the string have "abc" in it?)
+    // if (newWord.contains("Nov")){
+    //   System.out.println("True");
+    // } else {
+    //   System.out.println("False");
+    // }
+
+    System.out.println(newWord.contains("Nov"));
 
     // Iterate over the characters of the string, printing each one on a separate line
+    for (int i = 0; i < newWord.length(); i++){
+      char c = newWord.charAt(i);
+      System.out.println(c);
+    }
 
     // Create an ArrayList of Strings and assign it to a variable
+    ArrayList<String> list = new ArrayList<>();
 
     // Add multiple strings to the List (OK to do one-by-one)
+    list.add("Blue");
+    list.add("White");
+    list.add("Green");
+    list.add("Red");
+    System.out.println(list);
 
     // 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(", ", list);
+    System.out.println(joinedString);
 
     // Check whether two strings are equal
+    String s = list.get(1);
+    String s2 = list.get(2);
+    System.out.println(s.equals(s2));
 
     /*
      * Reminder!

toRefresh.md

@@ -2,4 +2,23 @@
 
 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.
 
-- 
+- float datatype
+- Syntax to create empty ArrayList/List
+- .get() to find element at index
+- .set() to replace an element at index
+- .size() to get number of elements in list
+- Collections.sort()
+- Arrays vs Lists
+- traditional for-loop for arrays
+- charAt() to return the character at index
+- .join() to join strings seperated by commas
+- .equals() syntax
+- iterate a HashSet
+- .put() for Maps
+- .get() access an item in HashMap
+- HashMap ordering
+- iterate a HashMap 
+- print both keys and values in Hashmap 
+- creating a constructor 
+- creating toString()
+- review Java OOP