Java Derusting Assignment

src/ArrayPractice.java

@@ -1,17 +1,27 @@
 public class ArrayPractice {
   public static void main(String[] args) {
     // Create an array of Strings of size 4
+    String[] words;
 
     // Set the value of the array at each index to be a different String
+    words={"word1","word2","word3","word4"};
     // It's OK to do this one-by-one
 
     // Get the value of the array at index 2
+    System.out.println(words[2]);
 
     // Get the length of the array
+    System.out.println(words.length);
 
     // Iterate over the array using a traditional for loop and print out each item
+    for (int i = 0; i < words.length; i++) {
+      System.out.println(words[i]);
+    }
 
     // Iterate over the array using a for-each loop and print out each item
+    for (String word : words) {
+      System.out.println(word);
+    }
 
     /*
      * Reminder!

src/ListPractice.java

@@ -1,35 +1,64 @@
-public class ListPractice {
+import java.util.ArrayList;
+import java.util.Collection;
+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> daysOfTheWeek = new ArrayList<String>();
+
     // Add 3 elements to the list (OK to do one-by-one)
+    daysOfTheWeek.add("Sunday");
+    daysOfTheWeek.add("Monday");
+    daysOfTheWeek.add("Tusday");
 
     // Print the element at index 1
 
+    System.out.println(daysOfTheWeek.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)
+    daysOfTheWeek.set(1, "Saturday");
 
     // Insert a new element at index 0 (the length of the list will change)
-
+    daysOfTheWeek.add(0, "Fryday");
     // Check whether the list contains a certain string
-
+      boolean found = false;
+     if daysOfTheWeek.contains("Monday"){
+      found = true;
+
+     }else{
+      found = false
+     }
+     System.out.println(found);
     // Iterate over the list using a traditional for-loop.
+    for(int i = 0; i < daysOfTheWeek.size(); i++){
+
     // Print each index and value on a separate line
+    System.out.println(daysOfTheWeek.get(i));
+    }
 
     // Sort the list using the Collections library
+    Collections.sort(daysOfTheWeek);
 
     // Iterate over the list using a for-each loop
-    // Print each value on a second line
+    for(String i : daysOfTheWeek){
+          // Print each value on a second line
+      System.out.println(i);
+    }
+
 
     /*
      * Usage tip!
      * 
-     * Use a traditional for-loop when you need to use the index or you need to iterate in an
+     * Use a traditional for-loop when you need to use the index or you need to
+     * iterate in an
      * unconventional order (e.g. backwards)
      * 
-     * Otherwise, if you're iterating the in the conventional order and don't need the
+     * Otherwise, if you're iterating the in the conventional order and don't need
+     * the
      * index values a for-each loop is cleaner.
      */
   }

src/MapPractice.java

@@ -1,40 +1,65 @@
-
+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
 
+    HashMap<String, Integer> studentRecord = new HashMap<>();
+    // assign it to a variable of type Map
+    Map<String, Integer> studentRecordMap = studentRecord;
     // Put 3 different key/value pairs in the Map
+
+    studentRecordMap.put("Saron", 112233);
+    studentRecordMap.put("Goitom", 123456);
+    studentRecordMap.put("Babi", 2345);
+
     // (it's OK to do this one-by-one)
 
     // Get the value associated with a given key in the Map
-
+    studentRecordMap.get("Saron");
     // Find the size (number of key/value pairs) of the Map
-
-    // Replace the value associated with a given key (the size of the Map shoukld not change)
+    studentRecordMap.size();
+    // Replace the value associated with a given key (the size of the Map shoukld
+    studentRecordMap.replace("Babi", 24567);
+    // not change)
 
     // Check whether the Map contains a given key
-
+    String key_search = "Azeb";
+    int value_search_search = 909;
+    boolean containsKey = studentRecordMap.containsKey(key_search);
+    System.out.println(containsKey);
     // Check whether the Map contains a given value
-
+    boolean containesValue = studentRecordMap.containsValue(value_search_search);
+    System.out.println(containesValue);
     // Iterate over the keys of the Map, printing each key
+    for (String i : studentRecordMap.keySet()) {
+      System.out.println(i);
+    }
 
     // Iterate over the values of the map, printing each value
+    for (Integer i : studentRecordMap.values()) {
+      System.out.println(i);
+    }
 
     // Iterate over the entries in the map, printing each key and value
+    for (String i : studentRecordMap.keySet()) {
+      System.out.println(i + ": " + studentRecordMap.get(i));
+    }
 
     /*
      * Usage tip!
      * 
      * Maps are great when you want a specific key to value mapping.
-     * Example: The key could be a person's name, and the value could be their phone number
+     * Example: The key could be a person's name, and the value could be their phone
+     * number
      * 
      * However if your keys are simple ascending 0-indexed integers with no gaps
      * (0, 1, 2, 3, 4...) then an array or List is likely a better choice.
      * Example: If you want to store the order of songs in a playlist.
      * 
-     * If you're finding that you're just wanting to store unordered values and the keys
+     * If you're finding that you're just wanting to store unordered values and the
+     * keys
      * are unimportant, a Set may be a better choice.
      * Example: If you want to hold the student ID numbers of everyone in a course,
      * and you don't care about any ordering.

src/NumberPractice.java

@@ -1,23 +1,34 @@
 public class NumberPractice {
   public static void main(String args[]) {
     // Create a float with a negative value and assign it to a variable
+    float negativeFloat = -1.4F;
 
     // Create an int with a positive value and assign it to a variable
+    int positiveInt = 9;
 
     // Use the modulo % operator to find the remainder when the int is divided by 3
+    int remainder = positiveInt % 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 (positiveInt % 2 == 0) {
+      System.out.println("Number is even");
+
+    }
+    if (positiveInt % 2 != 0) {
+      System.out.println("Number is Odd");
+    }
 
     // Divide the number by another number using integer division
+    int intdivision = positiveInt / 7;
 
     /*
      * Reminder!
      * 
      * When dividing ints, the result is rounded down.
-     * Example: 
+     * Example:
      * 7 / 3 = 2 when performing int division
      */
 

src/Person.java

@@ -3,17 +3,34 @@
  * the Person class.
  */
 
+import java.time.LocalDate;
+
 public class Person {
   // Declare a public String instance variable for the name of the person
+  public String name;
   // Declare a private int instance variable for the age of the person
-
-
+  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;
+  }
+
+  public String getName() {
+    return name;
+  }
 
+  public int getAge() {
+    return age;
+  }
 
   // Create a toString method that gives the name and age of the person
+  public String toString() {
+    return name + ":" + age;
 
+  }
 
   // Implement the below public instance method "birthYear"
   // There should NOT be any print statement in this method.
@@ -28,39 +45,52 @@ public class Person {
    * @return The year the person was born
    */
   // (create the instance method here)
-
+  public int birthYear(int age) {
+    int currentYear = LocalDate.now().getYear();
+    int yearBorn = currentYear - age;
+    return yearBorn;
+  }
 
   public static void main(String[] args) {
     // Create an instance of Person
+    Person person1 = new Person("Saron", 21);
 
     // Create another instance of Person with a different name and age and
     // assign it to a different variable
+    Person person2 = new Person("Babi", 28);
 
     // 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
+    person1.getName();
 
     // 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 = person1.birthYear(25);
 
     // In a separate statement, print the local variable holding the birth year.
-
+    System.out.println(currentyear);
     /**
      * Terminology!
      * 
      * A class is the overall definition, like a blueprint.
      * An instance is a specific object made according to that definition.
      * We use "instance" and "object" to mean the same thing.
      * 
-     * For example, if there is a Person class, we can make an instance of a specific person: Auberon.
+     * For example, if there is a Person class, we can make an instance of a
+     * specific person: Auberon.
      * 
-     * There can be many instances for the same class. For example: Auberon, Xinting, Baya are all
+     * There can be many instances for the same class. For example: Auberon,
+     * Xinting, Baya are all
      * different instances of the Person class.
      * 
-     * Each instance has its own instance variables: Auberon's age can be different from Baya's age.
+     * Each instance has its own instance variables: Auberon's age can be different
+     * from Baya's age.
      */
   }
 }

src/SetPractice.java

@@ -1,26 +1,41 @@
+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> books = new HashSet<>();
 
     // Add 3 elements to the set
+    books.add("To Kill a Mockingbird");
+    books.add("The Lord of the Flies");
+    books.add("The Lord of the Rings");
     // (It's OK to do it one-by-one)
 
     // Check whether the Set contains a given String
+    books.contains("The Lord of the Flies");
 
     // Remove an element from the Set
+    books.remove("To Kill a Mockingbird");
 
     // Get the size of the Set
+    books.size();
 
     // Iterate over the elements of the Set, printing each one on a separate line
+    for (String i : books) {
+      System.out.println(i);
+
+    }
 
     /*
      * Warning!
      * 
      * The iteration order over the items in a HashSet is NOT GUARANTEED.
      * 
-     * Even running the exact same program multiple times may give different results.
+     * Even running the exact same program multiple times may give different
+     * results.
      * Do not use a HashSet if order is important! You can use a TreeSet if you
-     * want items in sorted order, or an array or List if you want them in a specified
+     * want items in sorted order, or an array or List if you want them in a
+     * specified
      * order.
      * 
      * Also remember that sets do NOT have duplicates.