diff --git a/src/ArrayPractice.java b/src/ArrayPractice.java index bc58c83..a71bb00 100644 --- a/src/ArrayPractice.java +++ b/src/ArrayPractice.java @@ -1,18 +1,27 @@ 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] = "a"; + array[1] = "b"; + array[2] = "c"; + array[3] = "d"; // 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.print(array[i]); + } + System.out.println(); // Iterate over the array using a for-each loop and print out each item - + for(String str : array) { + System.out.print(str); + } /* * Reminder! * diff --git a/src/ListPractice.java b/src/ListPractice.java index f4de8e7..189f0cd 100644 --- a/src/ListPractice.java +++ b/src/ListPractice.java @@ -1,28 +1,47 @@ +import java.util.List; +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 - + List strList = new ArrayList<>(); // Add 3 elements to the list (OK to do one-by-one) - + strList.add("John"); + strList.add("Doe"); + strList.add("Happy"); // Print the element at index 1 - + System.out.println(strList.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) - + strList.set(1, "Sad"); // Insert a new element at index 0 (the length of the list will change) - + strList.add(0, "Angry"); + for(String s : strList) { + System.out.print(s + " "); + } + System.out.println(); // Check whether the list contains a certain string - + if(strList.contains("Sad")) { + System.out.println("True"); + } // Iterate over the list using a traditional for-loop. // Print each index and value on a separate line - + for(int i = 0; i < strList.size(); i++) { + System.out.println("Index: " + i); + System.out.println(strList.get(i)); + } // Sort the list using the Collections library - + Collections.sort(strList); // Iterate over the list using a for-each loop + for(String s : strList) { + System.out.print(s + " "); + } + System.out.println(); // Print each value on a second line - + for(String s : strList) { + System.out.println(s); + } /* * Usage tip! * diff --git a/src/MapPractice.java b/src/MapPractice.java index 7ebfeac..8ae8f0e 100644 --- a/src/MapPractice.java +++ b/src/MapPractice.java @@ -1,29 +1,47 @@ - +import java.util.Map; +import java.util.Collection; +import java.util.HashMap; +import java.util.Set; 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 hashMap = new HashMap<>(); // Put 3 different key/value pairs in the Map // (it's OK to do this one-by-one) - + hashMap.put("John", 18); + hashMap.put("Joseph", 40); + hashMap.put("David", 50); // Get the value associated with a given key in the Map - + System.out.println(hashMap.get("John")); // Find the size (number of key/value pairs) of the Map - + System.out.println(hashMap.size()); // Replace the value associated with a given key (the size of the Map shoukld not change) - + hashMap.replace("David", 50, 20); + System.out.println(hashMap.size()); // Check whether the Map contains a given key - + System.out.println(hashMap.containsKey("David")); // Check whether the Map contains a given value - + System.out.println(hashMap.containsValue(20)); // Iterate over the keys of the Map, printing each key - + Set keys = hashMap.keySet(); + for(String key : keys) { + System.out.print(key); + } // Iterate over the values of the map, printing each value - + Collection values = hashMap.values(); + for(int value : values) { + System.out.print(value); + } + System.out.println(); // Iterate over the entries in the map, printing each key and value - + for(Map.Entry entry : hashMap.entrySet()) { + String key = entry.getKey(); + int value = entry.getValue(); + System.out.println("Key: " + key + "Value: "+ value); + } /* * Usage tip! * diff --git a/src/NumberPractice.java b/src/NumberPractice.java index bbec2fe..a96c921 100644 --- a/src/NumberPractice.java +++ b/src/NumberPractice.java @@ -1,18 +1,24 @@ public class NumberPractice { public static void main(String args[]) { // Create a float with a negative value and assign it to a variable - + double negValue = -1.0; // Create an int with a positive value and assign it to a variable - + int posValue = 9; // Use the modulo % operator to find the remainder when the int is divided by 3 - + int remainder = posValue % 3; + System.out.println("Remainder: " + 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(posValue % 2 == 0) { + System.out.println("Number is even."); + } else { + System.out.println("Number is odd."); + } // Divide the number by another number using integer division - + int result = posValue / 3; + System.out.println(result); /* * Reminder! * diff --git a/src/Person.java b/src/Person.java index 8ab3f95..a438654 100644 --- a/src/Person.java +++ b/src/Person.java @@ -5,15 +5,22 @@ 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.age = age; + this.name = name; + } // Create a toString method that gives the name and age of the person - + @Override + public String toString() { + return "Name: " + name + "\nAge: " + age; + } // Implement the below public instance method "birthYear" // There should NOT be any print statement in this method. @@ -28,26 +35,28 @@ 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 person = new Person("Allen", 99); // Create another instance of Person with a different name and age and // assign it to a different variable - + Person person2 = new Person("Dude", 23); // Print the first person - + System.out.println(person.toString()); // Print the second person - + System.out.println(person2.toString()); // Get the name of the first person and store it in a local variable - + String firstPersonName = person.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 = person.birthYear(2025); // In a separate statement, print the local variable holding the birth year. - + System.out.println(birthYear); /** * Terminology! * diff --git a/src/SetPractice.java b/src/SetPractice.java index d2fc1c9..090e931 100644 --- a/src/SetPractice.java +++ b/src/SetPractice.java @@ -1,18 +1,24 @@ +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 hashSet = new HashSet<>(); // Add 3 elements to the set + hashSet.add("John"); + hashSet.add("Doe"); + hashSet.add("Vase"); // (It's OK to do it one-by-one) // Check whether the Set contains a given String - + System.out.println(hashSet.contains("Doe")); // Remove an element from the Set - + hashSet.remove("Doe"); // Get the size of the Set - + System.out.println(hashSet.size()); // Iterate over the elements of the Set, printing each one on a separate line - + for(String str : hashSet) { + System.out.println(str); + } /* * Warning! * diff --git a/src/StringPractice.java b/src/StringPractice.java index 8d87617..adb0f99 100644 --- a/src/StringPractice.java +++ b/src/StringPractice.java @@ -1,26 +1,33 @@ -public class StringPractice { +import java.util.List; +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 string = "Joseph"; // Find the length of the string - + System.out.println(string.length()); // Concatenate (add) two strings together and reassign the result - + string += " John"; + System.out.println(string); // Find the value of the character at index 3 - + System.out.println(string.charAt(3)); // Check whether the string contains a given substring (i.e. does the string have "abc" in it?) - + System.out.println(string.contains("ohn")); // Iterate over the characters of the string, printing each one on a separate line - + for(char c : string.toCharArray()) { + System.out.println(c); + } // Create an ArrayList of Strings and assign it to a variable - + List list = new ArrayList<>(); // Add multiple strings to the List (OK to do one-by-one) - + list.add("Doe"); + list.add("Flower"); + list.add("Allen"); // 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(list.toString()); // Check whether two strings are equal - + System.out.println(string.equals(list.get(0))); /* * Reminder! * diff --git a/toRefresh.md b/toRefresh.md index 163dcab..131e033 100644 --- a/toRefresh.md +++ b/toRefresh.md @@ -2,4 +2,4 @@ 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 +- Maps & OOP \ No newline at end of file