diff --git a/src/ArrayPractice.java b/src/ArrayPractice.java index bc58c83..de50fde 100644 --- a/src/ArrayPractice.java +++ b/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! * diff --git a/src/ListPractice.java b/src/ListPractice.java index f4de8e7..3c52687 100644 --- a/src/ListPractice.java +++ b/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 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! * diff --git a/src/MapPractice.java b/src/MapPractice.java index 7ebfeac..70a04a1 100644 --- a/src/MapPractice.java +++ b/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 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 entry : myMap.entrySet()) { + System.out.println(entry.getKey() + ", " + entry.getValue()); + } /* * Usage tip! * diff --git a/src/NumberPractice.java b/src/NumberPractice.java index bbec2fe..c963aab 100644 --- a/src/NumberPractice.java +++ b/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! * diff --git a/src/Person.java b/src/Person.java index 8ab3f95..27b7c0c 100644 --- a/src/Person.java +++ b/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! * diff --git a/src/SetPractice.java b/src/SetPractice.java index d2fc1c9..e56bb9a 100644 --- a/src/SetPractice.java +++ b/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 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! * diff --git a/src/StringPractice.java b/src/StringPractice.java index 8d87617..7932719 100644 --- a/src/StringPractice.java +++ b/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 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! * diff --git a/toRefresh.md b/toRefresh.md index 163dcab..9066db3 100644 --- a/toRefresh.md +++ b/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 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 + + '}'; + } + - \ No newline at end of file