Derusting - Java Review

src/ArrayPractice.java

@@ -2,21 +2,40 @@ public class ArrayPractice {
   public static void main(String[] args) {
     // Create an array of Strings of size 4
 
+    String[] words = 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
 
+    words[0] = "Array"; 
+    words[1] = "Practice";
+    words[2] = "For";
+    words[3] = "Class";
+
     // Get the value of the array at index 2
 
+    String valueAtIndex2 = words[2];
+    System.out.println("Value at index 2: " + valueAtIndex2);
+
     // Get the length of the array
 
+    int length = words.length;
+    System.out.println("Length of the array: " + length);
+
     // Iterate over the array using a traditional for loop and print out each item
 
+    System.out.println("Using a for-each loop:");
+    for (String word : words) {
+      System.out.println(word);
+    }
     // Iterate over the array using a for-each loop and print out each item
 
     /*
      * Reminder!
      * 
      * Arrays start at index 0
      */
+
+
   }
 }

src/ListPractice.java

@@ -1,28 +1,42 @@
+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> items = new ArrayList<>();
     // Add 3 elements to the list (OK to do one-by-one)
-
+    items.add("Number 1");
+    items.add("Number 2");
+    items.add("Number 3");
     // Print the element at index 1
-
+    System.out.println("Element at index 1: " + items.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)
-
+    items.set(1, "Practice");
+    System.out.println("Updated element at index 1: " + items.get(1));
     // Insert a new element at index 0 (the length of the list will change)
-
+    items.add(0, "Start");
+    System.out.println("Index 0: " + items);
     // Check whether the list contains a certain string
-
+    boolean containsCode = items.contains("Code");
+    System.out.println("Does this lest contain 'Code'? " + containsCode);
     // Iterate over the list using a traditional for-loop.
     // Print each index and value on a separate line
-
+    System.out.println("Using a traditional for-loop:");
+    for (int i = 0; i < items.size(); i++) {
+      System.out.println("Index " + i + ": " + items.get(i));
+    }
     // Sort the list using the Collections library
-
+    Collections.sort(items);
+    System.out.println("Sorted list: " + items);
     // Iterate over the list using a for-each loop
     // Print each value on a second line
-
+    System.out.println("Using a for-each loop:");
+    for (String item : items) {
+      System.out.println(item);
+    }
     /*
      * Usage tip!
      * 

src/MapPractice.java

@@ -1,29 +1,41 @@
-
+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> pointsScored = new HashMap<>();
     // Put 3 different key/value pairs in the Map
     // (it's OK to do this one-by-one)
-
+    pointsScored.put("Alex", 28);
+    pointsScored.put("Samuel", 30);
+    pointsScored.put("Jimmy", 42);
     // Get the value associated with a given key in the Map
-
+    System.out.println("Score for Alex: " + pointsScored.get("Alex"));
     // Find the size (number of key/value pairs) of the Map
-
+    System.out.println("Number of entries in the map: " + pointsScored.size());
     // Replace the value associated with a given key (the size of the Map shoukld not change)
-
+    pointsScored.put("Alex", 31);
+    System.out.println("Updated score for Alex: " + pointsScored.get("Alex"));
     // Check whether the Map contains a given key
-
+    System.out.println("Does the map contain the key 'Jimmy'? " + pointsScored.containsKey("Jimmy"));
     // Check whether the Map contains a given value
-
+    System.out.println("Does the map contain the value 42? " + pointsScored.containsValue(42));
     // Iterate over the keys of the Map, printing each key
-
+    System.out.println("Keys in the map:");
+    for (String key : pointsScored.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 : pointsScored.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 : pointsScored.entrySet()) {
+      System.out.println("Key: " + entry.getKey() + ", Value: " + entry.getValue());
+    }
     /*
      * Usage tip!
      * 

src/NumberPractice.java

@@ -1,17 +1,26 @@
 public class NumberPractice {
   public static void main(String args[]) {
     // Create a float with a negative value and assign it to a variable
-
+    float negativeFloat = -15.5f;
+    System.out.println("Negative float: " + negativeFloat);
     // Create an int with a positive value and assign it to a variable
-
+    int positiveInt = 19;
+    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 when " + positiveInt + " is 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(positiveInt + " is Even");
+    } else {
+      System.out.println(positiveInt + " is Odd");
+    }
     // Divide the number by another number using integer division
+    int result = positiveInt / 4; // Divide by 4
+    System.out.println("Result of integer division of " + positiveInt + " by 4: " + result);
 
     /*
      * Reminder!

src/Person.java

@@ -6,14 +6,21 @@
 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
-
+  @Override
+  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.
@@ -28,26 +35,29 @@ 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("Jimmy", 23);
     // Create another instance of Person with a different name and age and
     // assign it to a different variable
-
+    Person person2 = new Person("John", 29);
     // 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("Birth year of " + firstName + ": " + birthYear);
+
     /**
      * Terminology!
      * 

src/SetPractice.java

@@ -1,18 +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> mySet = new HashSet<>();
     // Add 3 elements to the set
     // (It's OK to do it one-by-one)
-
+    mySet.add("Cookies");
+    mySet.add("Cupcakes");
+    mySet.add("Brownies");
     // Check whether the Set contains a given String
-
+    String searchElement = "Cupcakes";
+    if (mySet.contains(searchElement)) {
+      System.out.println(searchElement + " is in the set.");
+    } else {
+      System.out.println(searchElement + " is not in the set.");
+    }
     // Remove an element from the Set
-
+    mySet.remove("Brownies");
+    System.out.println("After removing 'Brownies': " + mySet);
     // Get the size of the Set
-
+    int setSize = mySet.size();
+    System.out.println("Size of the set: " + setSize);
     // Iterate over the elements of the Set, printing each one on a separate line
-
+    System.out.println("Elements in the set:");
+    for (String element : mySet) {
+      System.out.println(element);
+    }
     /*
      * Warning!
      * 

src/StringPractice.java

@@ -1,26 +1,41 @@
+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 myString = "Hello";
     // Find the length of the string
-
+    int length = myString.length();
+    System.out.println("Length of the string: " + length);
     // Concatenate (add) two strings together and reassign the result
-
+    String newString = myString + " World";
+    System.out.println("Concatenated string: " + newString);
     // Find the value of the character at index 3
-
+    char charAtIndex3 = myString.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 containsSubstring = myString.contains("abc");
+    System.out.println("Does the string contain 'abc'? " + containsSubstring);
     // 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 < myString.length(); i++) {
+      System.out.println(myString.charAt(i));
+    }
     // Create an ArrayList of Strings and assign it to a variable
-
+    List<String> stringList = new ArrayList<>();
     // Add multiple strings to the List (OK to do one-by-one)
-
+    stringList.add("Apples");
+    stringList.add("Carrots");
+    stringList.add("Pomegranites");
     // 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(", ", stringList);
+    System.out.println("Joined list into a single string: " + joinedString);
     // Check whether two strings are equal
-
+    String anotherString = "Hello";
+    boolean areStringsEqual = myString.equals(anotherString);
+    System.out.println("Are the two strings equal? " + areStringsEqual);
     /*
      * Reminder!
      * 

toRefresh.md

@@ -2,4 +2,8 @@
 
 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.
 
-- 
+- String Practice
+- Set Practice
+- List Practice
+- Overall, I do need to look over all of these a little more to get them down
+- Because I am a little shaky on them.