diff --git a/src/ArrayPractice.java b/src/ArrayPractice.java index bc58c83..e570394 100644 --- a/src/ArrayPractice.java +++ b/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! diff --git a/src/ListPractice.java b/src/ListPractice.java index f4de8e7..5613f5b 100644 --- a/src/ListPractice.java +++ b/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 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! diff --git a/src/MapPractice.java b/src/MapPractice.java index 7ebfeac..76dcafe 100644 --- a/src/MapPractice.java +++ b/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 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! diff --git a/src/NumberPractice.java b/src/NumberPractice.java index bbec2fe..74acb75 100644 --- a/src/NumberPractice.java +++ b/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! diff --git a/src/Person.java b/src/Person.java index 8ab3f95..30045da 100644 --- a/src/Person.java +++ b/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! diff --git a/src/SetPractice.java b/src/SetPractice.java index d2fc1c9..c9c3270 100644 --- a/src/SetPractice.java +++ b/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 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! diff --git a/src/StringPractice.java b/src/StringPractice.java index 8d87617..c5d18c9 100644 --- a/src/StringPractice.java +++ b/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 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! diff --git a/toRefresh.md b/toRefresh.md index 163dcab..0761090 100644 --- a/toRefresh.md +++ b/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. -- \ No newline at end of file +- 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 \ No newline at end of file