Daniel Grabowski - Java Derusting

src/ArrayPractice.java

@@ -1,18 +1,26 @@
 public class ArrayPractice {
   public static void main(String[] args) {
     // Create an array of Strings of size 4
-
+    String[] myArray = new String[3];
     // Set the value of the array at each index to be a different String
     // It's OK to do this one-by-one
-
+    myArray[0] = "one";
+    myArray[1] = "two";
+    myArray[2] = "three";
     // Get the value of the array at index 2
-
+    System.out.println("Value at index 2 - " + myArray[2]);
     // Get the length of the array
-
+    System.out.println("Length of myArray - " + myArray.length);
     // Iterate over the array using a traditional for loop and print out each item
-
+    System.out.println("--Printing values in myArray (for loop)--");
+    for (int i = 0; i < myArray.length; i++) {
+      System.out.println(myArray[i]);
+    }
     // Iterate over the array using a for-each loop and print out each item
-
+    System.out.println("--Printing values in myArray (for each loop)--");
+    for (String word : myArray) {
+      System.out.println(word);
+    }
     /*
      * Reminder!
      * 

src/ListPractice.java

@@ -1,28 +1,45 @@
+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> myList = new ArrayList<>();
     // Add 3 elements to the list (OK to do one-by-one)
-
+    myList.add("one");
+    myList.add("two");
+    myList.add("three");
     // Print the element at index 1
-
+    System.out.println(myList.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)
-
+    myList.set(1, "newTwo");
+    System.out.println(myList);
     // Insert a new element at index 0 (the length of the list will change)
-
+    myList.add(0, "zero");
+    System.out.println(myList);
     // Check whether the list contains a certain string
-
+    if (myList.contains("zero")) {
+      System.out.println("String 'zero' found");
+    }
+    else {
+      System.out.println("String 'zero' not found");
+    }
     // Iterate over the list using a traditional for-loop.
     // Print each index and value on a separate line
-
+    System.out.println("--Printing elements unsorted--");
+    for (int i = 0; i < myList.size(); i++) {
+      System.out.println(myList.get(i));
+    }
     // Sort the list using the Collections library
-
+    Collections.sort(myList);
     // Iterate over the list using a for-each loop
     // Print each value on a second line
-
+    System.out.println("--Printing elements sorted--");
+    for (String word : myList) {
+      System.out.println(word);
+    }
     /*
      * Usage tip!
      * 

src/MapPractice.java

@@ -1,29 +1,52 @@
-
+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> myMap = new HashMap<>();
     // Put 3 different key/value pairs in the Map
     // (it's OK to do this one-by-one)
-
+    myMap.put("one", 1);
+    myMap.put("two", 2);
+    myMap.put("three", 3);
+    System.out.println(myMap);
     // Get the value associated with a given key in the Map
-
+    System.out.println("The value for key 'one' is - " + myMap.get("one"));
     // Find the size (number of key/value pairs) of the Map
-
+    System.out.println("The size of myMap is - " + myMap.size());
     // Replace the value associated with a given key (the size of the Map shoukld not change)
-
+    myMap.put("three", 33);
+    System.out.println("New myMap values are - " + myMap);
     // Check whether the Map contains a given key
-
+    if (myMap.containsKey("one")) {
+      System.out.println("myMap does contain the key 'one'");
+    }
+    else {
+      System.out.println("myMap does not contain the key 'one'");
+    }
     // Check whether the Map contains a given value
-
+    if (myMap.containsValue(1)) {
+      System.out.println("myMap does contain the value 'one'");
+    }
+    else {
+      System.out.println("myMap does not contain the key 'one'");
+    }
     // Iterate over the keys of the Map, printing each key
-
+    System.out.println("--Printing all keys in myMap--");
+    for (String key : myMap.keySet()) {
+      System.out.println(key);
+    }
     // Iterate over the values of the map, printing each value
-
+    System.out.println("--Printing all values in myMap--");
+    for (int key : myMap.values()) {
+      System.out.println(key);
+    }
     // Iterate over the entries in the map, printing each key and value
-
+    System.out.println("--Printing all key/value pairs in myMap--");
+    for (Map.Entry<String, Integer> entry : myMap.entrySet()) {
+      System.out.println(entry.getKey() + ", " + entry.getValue());
+    }
     /*
      * Usage tip!
      * 

src/NumberPractice.java

@@ -1,18 +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 negFloat = -1.5F;
+    System.out.println(negFloat);
     // Create an int with a positive value and assign it to a variable
-
+    int posInt = 7;
+    System.out.println(posInt);
     // Use the modulo % operator to find the remainder when the int is divided by 3
-
+    int remainder = 1 % 3;
+    System.out.println(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 dividedInt = posInt / 2;
+    System.out.println(dividedInt);
     /*
      * 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: " + this.name + " - Age: " + this.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 - this.age;
+  }
 
   public static void main(String[] args) {
     // Create an instance of Person
-
+    Person personOne = new Person("Daniel", 27);
     // Create another instance of Person with a different name and age and
     // assign it to a different variable
-
+    Person personTwo = new Person("Gator", 30);
     // Print the first person
-
+    System.out.println("personOne - " + personOne);
     // Print the second person
-
+    System.out.println("personTwo - " + personTwo);
     // Get the name of the first person and store it in a local variable
-
+    String personOneName = personOne.name;
+    System.out.println("The name of personOne is - " + personOneName);
     // 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 personOneBirthYear = personOne.birthYear(2025);
     // In a separate statement, print the local variable holding the birth year.
-
+    System.out.println("The birth year of personOne is - " + personOneBirthYear);
     /**
      * Terminology!
      * 

src/SetPractice.java

@@ -1,18 +1,32 @@
+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("one");
+    mySet.add("two");
+    mySet.add("three");
+    System.out.println(mySet);
     // Check whether the Set contains a given String
-
+    if (mySet.contains("one")) {
+      System.out.println("mySet does contain string 'one'");
+    }
+    else {
+      System.out.println("mySet does not contain string 'one'");
+    }
     // Remove an element from the Set
-
+    mySet.remove("three");
+    System.out.println(mySet);
     // Get the size of the Set
-
+    System.out.println("The size of the set is - " + mySet.size());
     // Iterate over the elements of the Set, printing each one on a separate line
-
+    System.out.println("--Printing all elements in mySet--");
+    for (String word : mySet) {
+      System.out.println(word);
+    }
     /*
      * Warning!
      * 

src/StringPractice.java

@@ -1,26 +1,46 @@
+import java.util.*;
+
 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 = "daniel";
+    System.out.println("myString is - " + myString);
     // Find the length of the string
-
+    System.out.println("The length of myString is - " + myString.length());
     // Concatenate (add) two strings together and reassign the result
-
+    String myStringTwo = "grabowski";
+    String fullname = myString + myStringTwo;
+    System.out.println("The concatenated string is - " + fullname);
     // Find the value of the character at index 3
-
+    System.out.println("The value of the character at index 3 is - " + myString.charAt(3));
     // Check whether the string contains a given substring (i.e. does the string have "abc" in it?)
-
+    if (myString.contains("dan")) {
+      System.out.println("myString does contain substring 'dan'");
+    }
+    else {
+      System.out.println("myString does not contain substring 'dan'");
+    }
     // Iterate over the characters of the string, printing each one on a separate line
-
+    System.out.println("--Printing all characters in myString");
+    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> myList = new ArrayList<>();
     // Add multiple strings to the List (OK to do one-by-one)
-
+    myList.add("one");
+    myList.add("two");
+    myList.add("three");
     // 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
-
+    System.out.println("All words in myList concatenated - " + myList.get(0) + ", ".concat(myList.get(1)) + ", ".concat(myList.get(2)));
     // Check whether two strings are equal
-
+    if (myString.equals(myStringTwo)) {
+      System.out.println("myString is equal to myStringTwo");
+    }
+    else {
+      System.out.println("myString is not equal to myStringTwo");
+    }
     /*
      * Reminder!
      * 

toRefresh.md

@@ -2,4 +2,52 @@
 
 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.
 
+
+Lists
+----------
+ArrayList replace - myList.set(int index, E element)
+Adding at index - myList.add(int index, E element)
+Collections.sort(myList)
+
+
+Arrays
+----------
+Creating an array {
+    String[] myArray = new String[5]; // Where 5 is the length of the array
+}
+
+
+Strings
+----------
+Concatenation method - myString.concat(myStringTwo)
+
+
+Maps
+----------
+For itteration {
+    map.keySet() // To itterate keys
+    map.values() // To itterate values
+    map.entrySet() // To itterate both
+}
+
+entrySet() example {
+    for (Map.Entry<String, Integer> entry : map.entrySet()) {
+    String key = entry.getKey();
+    Integer value = entry.getValue();
+    // do something with key and value
+}
+}
+
+
+Classes and objects/instances
+----------
+Overriding the toString method:
+@Override
+public String toString() {
+    return "Person{" +
+                "name='" + name + '\'' +
+                ", age=" + age +
+                '}';
+    }
+
 -