diff --git a/src/ArrayPractice.java b/src/ArrayPractice.java index bc58c83..250df15 100644 --- a/src/ArrayPractice.java +++ b/src/ArrayPractice.java @@ -1,18 +1,32 @@ + import java.util.Arrays; public class ArrayPractice { + public static void main(String[] args) { // Create an array of Strings of size 4 + String[] arr = 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 + arr[0] = "This"; + arr[1] = "is"; + arr[2] = "an"; + arr[3] = "array"; // Get the value of the array at index 2 + String valueAtIndex2 = arr[2]; // Receiving the value at index 2 // Get the length of the array + int lengthOfArray = arr.length; // Length of array // Iterate over the array using a traditional for loop and print out each item + for(int i = 0; i < arr.length; i++){ + System.out.println(arr[i]); + } // Iterate over the array using a for-each loop and print out each item - + for(String item : arr){ + System.out.println(item); + } /* * Reminder! * diff --git a/src/ListPractice.java b/src/ListPractice.java index f4de8e7..4a509e6 100644 --- a/src/ListPractice.java +++ b/src/ListPractice.java @@ -1,27 +1,46 @@ +import java.util.ArrayList; +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 myList = new ArrayList<>(); // Add 3 elements to the list (OK to do one-by-one) + myList.add("First"); + myList.add("Second"); + myList.add("Third"); // Print the element at index 1 + System.out.println(myList.get(1)); // Getting the element at index 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, "replaced value"); // Replacing the element at index 1 with .set() // Insert a new element at index 0 (the length of the list will change) + myList.add(0, "new value here"); // Inserting a new element // Check whether the list contains a certain string + boolean containsString = myList.contains("First"); // Checking if the list contains "First" + System.out.println("List contains a string: " + containsString); // Iterate over the list using a traditional for-loop. // Print each index and value on a separate line + for(int i = 0; i < myList.size(); i++){ + System.out.println("Index: " + i + "\n" + "Value: " + myList.get(i)); + } // Sort the list using the Collections library + Collections.sort(myList); // Sorting the list // Iterate over the list using a for-each loop // Print each value on a second line + for(String item : myList){ + System.out.println(item); + } /* * Usage tip! diff --git a/src/MapPractice.java b/src/MapPractice.java index 7ebfeac..00fa62c 100644 --- a/src/MapPractice.java +++ b/src/MapPractice.java @@ -1,28 +1,50 @@ +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 + Map myMap = new HashMap<>(); + // Put 3 different key/value pairs in the Map // (it's OK to do this one-by-one) + myMap.put("First", 1); + myMap.put("Second", 2); + myMap.put("Third", 3); // Get the value associated with a given key in the Map + int valueForKey = myMap.get("Second"); // Getting the value for the key "Second" // Find the size (number of key/value pairs) of the Map + int mapSize = myMap.size(); // Size of the map // Replace the value associated with a given key (the size of the Map shoukld not change) + myMap.put("Second", 22); // Replacing the value for the key "Second" // Check whether the Map contains a given key + boolean containsKey = myMap.containsKey("First"); + System.out.println("Map contains key: " + containsKey); // Check whether the Map contains a given value + boolean containsValue = myMap.containsValue(3); + System.out.println("Map contains value: " + containsValue); // Iterate over the keys of the Map, printing each key - + for(String key : myMap.keySet()){ // using keySet() to grab all keys + System.out.println(key); + } // Iterate over the values of the map, printing each value + for(Integer value : myMap.values()) { // using values() to grab all values, with Integer type + System.out.println(value); + } // Iterate over the entries in the map, printing each key and value + for(Map.Entry entry : myMap.entrySet()) { // using entrySet() to grab all entries with Entry type. + System.out.println("Key: " + entry.getKey() + "\n" + "Value: " + entry.getValue()); + } /* * Usage tip! diff --git a/src/NumberPractice.java b/src/NumberPractice.java index bbec2fe..de86dfe 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 negativeFloat = -3.14f; // Creating a float with a negative value // Create an int with a positive value and assign it to a variable + int posInt = 42; // Creating an int with a positive value // Use the modulo % operator to find the remainder when the int is divided by 3 + int remainder = posInt % 3; // Remainder given 3 as the divisor + System.out.println(remainder); // printing 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 divisionResult = posInt / 5; // Integer division + System.out.println(divisionResult); // printing result of integer division /* * Reminder! diff --git a/src/Person.java b/src/Person.java index 8ab3f95..52d1856 100644 --- a/src/Person.java +++ b/src/Person.java @@ -6,13 +6,22 @@ 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 + "\n" + "Age: " + age; + } // Implement the below public instance method "birthYear" @@ -28,25 +37,36 @@ public class Person { * @return The year the person was born */ // (create the instance method here) + public int birthYear(int year){ + int birthYear = year - age; + return birthYear; + } public static void main(String[] args) { // Create an instance of Person + Person person1 = new Person("Jaron", 19); // creating new instance of Person object // Create another instance of Person with a different name and age and // assign it to a different variable + Person person2 = new Person("Maxwell", 10); // creating another instance of Person object // 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 name1 = 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 " + name1 + ": " + birthYear); /** * Terminology! diff --git a/src/SetPractice.java b/src/SetPractice.java index d2fc1c9..46bb5c2 100644 --- a/src/SetPractice.java +++ b/src/SetPractice.java @@ -1,17 +1,31 @@ +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 mySet = new HashSet<>(); + // Add 3 elements to the set // (It's OK to do it one-by-one) + mySet.add("First"); + mySet.add("Second"); + mySet.add("Third"); // Check whether the Set contains a given String + boolean containsString = mySet.contains("Second"); // checking if a given string exists in set + System.out.println("Set contains string: " + containsString); // Remove an element from the Set + mySet.remove("Second"); // Get the size of the Set + int setSize = mySet.size(); // size of the set // Iterate over the elements of the Set, printing each one on a separate line + for(String item : mySet){ // using for-each loop to iterate over the set + System.out.println(item); + } /* * Warning! diff --git a/src/StringPractice.java b/src/StringPractice.java index 8d87617..c2098df 100644 --- a/src/StringPractice.java +++ b/src/StringPractice.java @@ -1,25 +1,46 @@ -public class StringPractice { +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 fiveLetterString = "Hello"; // Find the length of the string + fiveLetterString.length(); + // Concatenate (add) two strings together and reassign the result + String newString = fiveLetterString + "World"; // Concatenating two strings together // Find the value of the character at index 3 + char charAtIndex3 = fiveLetterString.charAt(3); // Getting the character at index 3 // Check whether the string contains a given substring (i.e. does the string have "abc" in it?) + boolean checkSubstring = fiveLetterString.contains("llo"); // Iterate over the characters of the string, printing each one on a separate line + for(int i = 0; i < fiveLetterString.length(); i++){ + System.out.println(fiveLetterString.charAt(i)); // using charAt to print each index + } // Create an ArrayList of Strings and assign it to a variable + ArrayList myArrayList = new ArrayList<>(); // Add multiple strings to the List (OK to do one-by-one) + myArrayList.add("First"); + myArrayList.add("Second"); + myArrayList.add("Third"); // 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(",", myArrayList); // Joining the strings in the list together with commas using .join(); // Check whether two strings are equal + String string1 = "Hello"; + String string2 = "world"; + + boolean stringsEqual = string1.equals(string2); // Checking if two strings are equal with .equals() /* * Reminder!