Introduction to Java Collections
In Java, the collections framework provides a set of interfaces and classes that allow you to store, manipulate, and retrieve collections of objects. These collections can be used to efficiently manage and work with groups of related data.
One of the key benefits of using collections in Java is the ability to use pre-defined data structures that are optimized for specific use cases. This can greatly simplify and enhance the efficiency of your code.
The Java collections framework includes various interfaces and classes, such as:
ArrayList: A resizable array implementation of theListinterface.LinkedList: A doubly-linked list implementation of theListinterface.HashMap: A hash table implementation of theMapinterface.Stack: A stack implementation of theListinterface.Queue: An interface that specifies a simple queue (first-in, first-out) data structure.Set: An interface that represents an unordered collection of unique elements.TreeSet: A sorted set implementation of theSetinterface.
Let's take a look at an example that demonstrates the usage of some of these collection classes in Java:
1// Example of using various Java collection classes
2ArrayList<String> arrayList = new ArrayList<>();
3LinkedList<String> linkedList = new LinkedList<>();
4HashMap<String, Integer> hashMap = new HashMap<>();
5Stack<String> stack = new Stack<>();
6Queue<String> queue = new LinkedList<>();
7Set<String> set = new TreeSet<>();
8
9// Add elements to ArrayList
10arrayList.add("Element 1");
11arrayList.add("Element 2");
12arrayList.add("Element 3");
13
14// Add elements to LinkedList
15linkedList.add("Element A");
16linkedList.add("Element B");
17linkedList.add("Element C");
18
19// Add element to HashMap
20hashMap.put("Key 1", 1);
21hashMap.put("Key 2", 2);
22hashMap.put("Key 3", 3);
23
24// Push elements to Stack
25stack.push("Element X");
26stack.push("Element Y");
27stack.push("Element Z");
28
29// Add elements to Queue
30queue.add("Element I");
31queue.add("Element II");
32queue.add("Element III");
33
34// Add elements to Set
35set.add("Element Alpha");
36set.add("Element Bravo");
37set.add("Element Charlie");xxxxxxxxxx}import java.util.ArrayList;import java.util.LinkedList;import java.util.HashMap;import java.util.Stack;import java.util.Queue;import java.util.Set;import java.util.TreeSet;public class Main { public static void main(String[] args) { // Example of using various Java collection classes ArrayList<String> arrayList = new ArrayList<>(); LinkedList<String> linkedList = new LinkedList<>(); HashMap<String, Integer> hashMap = new HashMap<>(); Stack<String> stack = new Stack<>(); Queue<String> queue = new LinkedList<>(); Set<String> set = new TreeSet<>(); // Add elements to ArrayList arrayList.add("Element 1"); arrayList.add("Element 2"); arrayList.add("Element 3"); // Add elements to LinkedList linkedList.add("Element A"); linkedList.add("Element B"); linkedList.add("Element C");Let's test your knowledge. Fill in the missing part by typing it in.
In Java, an ArrayList is a ___ implementation of the List interface.
Write the missing line below.
ArrayList
The ArrayList class in Java is a resizable array implementation of the List interface. It provides various methods that allow you to add, remove, and access elements in the ArrayList.
To use the ArrayList class, you need to import the java.util.ArrayList package.
Here's an example that demonstrates the usage of the ArrayList class:
1import java.util.ArrayList;
2
3public class Main {
4
5 public static void main(String[] args) {
6 // Create an ArrayList
7 ArrayList<String> arrayList = new ArrayList<>();
8
9 // Add elements to the ArrayList
10 arrayList.add("Element 1");
11 arrayList.add("Element 2");
12 arrayList.add("Element 3");
13
14 // Access elements in the ArrayList
15 String element = arrayList.get(1);
16 System.out.println("Element at index 1: " + element);
17
18 // Update an element
19 arrayList.set(0, "Updated Element");
20
21 // Remove an element
22 arrayList.remove(2);
23
24 // Check if an element exists
25 boolean exists = arrayList.contains("Element 2");
26 System.out.println("Element 2 exists: " + exists);
27
28 // Get the size of the ArrayList
29 int size = arrayList.size();
30 System.out.println("Size of the ArrayList: " + size);
31 }
32
33}xxxxxxxxxx}import java.util.ArrayList;public class Main { public static void main(String[] args) { // Create an ArrayList ArrayList<String> arrayList = new ArrayList<>(); // Add elements to the ArrayList arrayList.add("Element 1"); arrayList.add("Element 2"); arrayList.add("Element 3"); // Access elements in the ArrayList String element = arrayList.get(1); System.out.println("Element at index 1: " + element); // Update an element arrayList.set(0, "Updated Element"); // Remove an element arrayList.remove(2); // Check if an element exists boolean exists = arrayList.contains("Element 2"); System.out.println("Element 2 exists: " + exists); // Get the size of the ArrayList int size = arrayList.size();Are you sure you're getting this? Fill in the missing part by typing it in.
The ArrayList class in Java is a ___ array implementation of the List interface.
Write the missing line below.
LinkedList
The LinkedList class in Java is a doubly linked list implementation of the List interface. It provides various methods that allow you to add, remove, and access elements in the LinkedList.
To use the LinkedList class, you need to import the java.util.LinkedList package.
Here's an example that demonstrates the usage of the LinkedList class:
1class Main {
2
3 public static void main(String[] args) {
4 // Create a LinkedList
5 LinkedList<String> linkedList = new LinkedList<>();
6
7 // Add elements to the LinkedList
8 linkedList.add("Element 1");
9 linkedList.add("Element 2");
10 linkedList.add("Element 3");
11
12 // Access elements in the LinkedList
13 String element = linkedList.get(1);
14 System.out.println("Element at index 1: " + element);
15
16 // Update an element
17 linkedList.set(0, "Updated Element");
18
19 // Remove an element
20 linkedList.remove(2);
21
22 // Check if an element exists
23 boolean exists = linkedList.contains("Element 2");
24 System.out.println("Element 2 exists: " + exists);
25
26 // Get the size of the LinkedList
27 int size = linkedList.size();
28 System.out.println("Size of the LinkedList: " + size);
29 }
30
31}xxxxxxxxxx}class Main { public static void main(String[] args) { // Create a LinkedList LinkedList<String> linkedList = new LinkedList<>(); // Add elements to the LinkedList linkedList.add("Element 1"); linkedList.add("Element 2"); linkedList.add("Element 3"); // Access elements in the LinkedList String element = linkedList.get(1); System.out.println("Element at index 1: " + element); // Update an element linkedList.set(0, "Updated Element"); // Remove an element linkedList.remove(2); // Check if an element exists boolean exists = linkedList.contains("Element 2"); System.out.println("Element 2 exists: " + exists); // Get the size of the LinkedList int size = linkedList.size(); System.out.println("Size of the LinkedList: " + size); }Let's test your knowledge. Fill in the missing part by typing it in.
The LinkedList class in Java is a ____ linked list implementation of the List interface.
Write the missing line below.
HashMap
The HashMap class in Java is an implementation of the Map interface that stores key-value pairs. It provides fast access and retrieval of elements based on their keys.
To use the HashMap class, you need to import the java.util.HashMap package.
Here's an example that demonstrates the usage of the HashMap class:
1class Main {
2
3 public static void main(String[] args) {
4 // Create a HashMap
5 HashMap<String, Integer> hashMap = new HashMap<>();
6
7 // Add key-value pairs to the HashMap
8 hashMap.put("John", 25);
9 hashMap.put("Sarah", 30);
10 hashMap.put("Emily", 28);
11
12 // Access values from the HashMap
13 int johnAge = hashMap.get("John");
14 System.out.println("John's age: " + johnAge);
15
16 // Check if a key exists in the HashMap
17 boolean exists = hashMap.containsKey("Sarah");
18 System.out.println("Sarah exists: " + exists);
19
20 // Remove a key-value pair from the HashMap
21 hashMap.remove("Emily");
22
23 // Update the value for a key in the HashMap
24 hashMap.put("John", 26);
25
26 // Get the size of the HashMap
27 int size = hashMap.size();
28 System.out.println("Size of the HashMap: " + size);
29 }
30
31}xxxxxxxxxx}import java.util.HashMap;public class Main { public static void main(String[] args) { // Create a HashMap HashMap<String, Integer> hashMap = new HashMap<>(); // Add key-value pairs to the HashMap hashMap.put("John", 25); hashMap.put("Sarah", 30); hashMap.put("Emily", 28); // Access values from the HashMap int johnAge = hashMap.get("John"); System.out.println("John's age: " + johnAge); // Check if a key exists in the HashMap boolean exists = hashMap.containsKey("Sarah"); System.out.println("Sarah exists: " + exists); // Remove a key-value pair from the HashMap hashMap.remove("Emily"); // Update the value for a key in the HashMap hashMap.put("John", 26); // Get the size of the HashMap int size = hashMap.size();Let's test your knowledge. Fill in the missing part by typing it in.
The ______ class in Java is an implementation of the Map interface that stores key-value pairs. It provides fast access and retrieval of elements based on their keys.
Write the missing line below.
Stack
The Stack class in Java represents a Last-In-First-Out (LIFO) data structure, where the last element added to the stack is the first one to be removed. It provides methods to push elements onto the stack, pop elements from the stack, get the top element without removing it, check if the stack is empty, and get the size of the stack.
To use the Stack class, you need to import the java.util.Stack package.
Here's an example that demonstrates the usage of the Stack class:
1import java.util.Stack;
2
3public class Main {
4
5 public static void main(String[] args) {
6 // Create a stack
7 Stack<Integer> stack = new Stack<>();
8
9 // Push elements onto the stack
10 stack.push(5);
11 stack.push(10);
12 stack.push(15);
13
14 // Pop an element from the stack
15 int element = stack.pop();
16 System.out.println("Popped element: " + element);
17
18 // Get the top element of the stack without removing
19 int top = stack.peek();
20 System.out.println("Top element: " + top);
21
22 // Check if the stack is empty
23 boolean isEmpty = stack.isEmpty();
24 System.out.println("Is stack empty: " + isEmpty);
25
26 // Get the size of the stack
27 int size = stack.size();
28 System.out.println("Size of the stack: " + size);
29 }
30
31}xxxxxxxxxx}import java.util.Stack;public class Main { public static void main(String[] args) { // Create a stack Stack<Integer> stack = new Stack<>(); // Push elements onto the stack stack.push(5); stack.push(10); stack.push(15); // Pop an element from the stack int element = stack.pop(); System.out.println("Popped element: " + element); // Get the top element of the stack without removing int top = stack.peek(); System.out.println("Top element: " + top); // Check if the stack is empty boolean isEmpty = stack.isEmpty(); System.out.println("Is stack empty: " + isEmpty); // Get the size of the stack int size = stack.size(); System.out.println("Size of the stack: " + size); }Try this exercise. Fill in the missing part by typing it in.
In Java, the Stack class is a ____ data structure.
Write the missing line below.
Queue
The Queue interface in Java represents a collection of elements that supports insertion, removal, and retrieval operations. It follows the First-In-First-Out (FIFO) order, where the element that is inserted first is the first one to be removed.
To use the Queue interface, you need to import the java.util.Queue package.
Here's an example that demonstrates the usage of the Queue interface:
1import java.util.LinkedList;
2import java.util.Queue;
3
4public class Main {
5
6 public static void main(String[] args) {
7 // Create a queue
8 Queue<String> queue = new LinkedList<>();
9
10 // Adding elements to the queue
11 queue.add("Alice");
12 queue.add("Bob");
13 queue.add("Charlie");
14
15 // Printing the queue
16 System.out.println("Queue: " + queue);
17
18 // Accessing the front element of the queue
19 String frontElement = queue.peek();
20 System.out.println("Front element: " + frontElement);
21
22 // Removing elements from the queue
23 String removedElement = queue.poll();
24 System.out.println("Removed element: " + removedElement);
25
26 // Printing the updated queue
27 System.out.println("Updated Queue: " + queue);
28
29 // Checking if the queue is empty
30 boolean isEmpty = queue.isEmpty();
31 System.out.println("Is Queue empty: " + isEmpty);
32
33 // Checking the size of the queue
34 int size = queue.size();
35 System.out.println("Size of the queue: " + size);
36 }
37
38}xxxxxxxxxx}import java.util.LinkedList;import java.util.Queue;public class Main { public static void main(String[] args) { // Create a queue Queue<String> queue = new LinkedList<>(); // Adding elements to the queue queue.add("Alice"); queue.add("Bob"); queue.add("Charlie"); // Printing the queue System.out.println("Queue: " + queue); // Accessing the front element of the queue String frontElement = queue.peek(); System.out.println("Front element: " + frontElement); // Removing elements from the queue String removedElement = queue.poll(); System.out.println("Removed element: " + removedElement); // Printing the updated queue System.out.println("Updated Queue: " + queue); // Checking if the queue is emptyTry this exercise. Click the correct answer from the options.
Which of the following is an essential property of a Queue?
Click the option that best answers the question.
- First-In-First-Out (FIFO)
- Last-In-First-Out (LIFO)
- Random access
- Unordered
Set
The Set interface in Java represents a collection of unique elements. It does not allow duplicate elements in the collection. The Set interface is a part of the Java Collections Framework and provides several useful methods for working with sets.
To use the Set interface, you need to import the java.util.Set package.
Here's an example that demonstrates the usage of the Set interface:
1import java.util.HashSet;
2import java.util.Set;
3
4public class Main {
5
6 public static void main(String[] args) {
7 // Create a set
8 Set<String> set = new HashSet<>();
9
10 // Adding elements to the set
11 set.add("Apple");
12 set.add("Banana");
13 set.add("Orange");
14 set.add("Apple");
15
16 // Printing the set
17 System.out.println("Set: " + set);
18
19 // Checking if an element exists in the set
20 boolean contains = set.contains("Banana");
21 System.out.println("Contains 'Banana' in set: " + contains);
22
23 // Removing an element from the set
24 boolean removed = set.remove("Orange");
25 System.out.println("Removed 'Orange' from set: " + removed);
26
27 // Printing the updated set
28 System.out.println("Updated Set: " + set);
29
30 // Checking the size of the set
31 int size = set.size();
32 System.out.println("Size of the set: " + size);
33 }
34
35}xxxxxxxxxx}import java.util.HashSet;import java.util.Set;public class Main { public static void main(String[] args) { // Create a set Set<String> set = new HashSet<>(); // Adding elements to the set set.add("Apple"); set.add("Banana"); set.add("Orange"); set.add("Apple"); // Printing the set System.out.println("Set: " + set); // Checking if an element exists in the set boolean contains = set.contains("Banana"); System.out.println("Contains 'Banana' in set: " + contains); // Removing an element from the set boolean removed = set.remove("Orange"); System.out.println("Removed 'Orange' from set: " + removed); // Printing the updated set System.out.println("Updated Set: " + set);Let's test your knowledge. Is this statement true or false?
The Set interface in Java allows duplicate elements to be stored.
Press true if you believe the statement is correct, or false otherwise.
TreeSet
The TreeSet class in Java is an implementation of the Set interface that stores elements in a sorted order. Elements in a TreeSet are arranged according to their natural ordering or a specified comparator.
To use the TreeSet class, you need to import the java.util.TreeSet package.
Here's an example that demonstrates the usage of the TreeSet class:
1import java.util.TreeSet;
2
3public class Main {
4
5 public static void main(String[] args) {
6 // Create a TreeSet
7 TreeSet<Integer> treeSet = new TreeSet<>();
8
9 // Adding elements to the TreeSet
10 treeSet.add(5);
11 treeSet.add(2);
12 treeSet.add(7);
13 treeSet.add(9);
14 treeSet.add(1);
15
16 // Printing the TreeSet
17 System.out.println("TreeSet: " + treeSet);
18
19 // Getting the first element
20 int firstElement = treeSet.first();
21 System.out.println("First Element: " + firstElement);
22
23 // Getting the last element
24 int lastElement = treeSet.last();
25 System.out.println("Last Element: " + lastElement);
26
27 // Checking if an element exists in the TreeSet
28 boolean contains = treeSet.contains(7);
29 System.out.println("Contains 7 in TreeSet: " + contains);
30
31 // Removing an element from the TreeSet
32 boolean removed = treeSet.remove(2);
33 System.out.println("Removed 2 from TreeSet: " + removed);
34
35 // Printing the updated TreeSet
36 System.out.println("Updated TreeSet: " + treeSet);
37
38 // Checking the size of the TreeSet
39 int size = treeSet.size();
40 System.out.println("Size of the TreeSet: " + size);
41 }
42
43}xxxxxxxxxx}import java.util.TreeSet;public class Main { public static void main(String[] args) { // Create a TreeSet TreeSet<Integer> treeSet = new TreeSet<>(); // Adding elements to the TreeSet treeSet.add(5); treeSet.add(2); treeSet.add(7); treeSet.add(9); treeSet.add(1); // Printing the TreeSet System.out.println("TreeSet: " + treeSet); // Getting the first element int firstElement = treeSet.first(); System.out.println("First Element: " + firstElement); // Getting the last element int lastElement = treeSet.last(); System.out.println("Last Element: " + lastElement); // Checking if an element exists in the TreeSet boolean contains = treeSet.contains(7); System.out.println("Contains 7 in TreeSet: " + contains);Are you sure you're getting this? Is this statement true or false?
The TreeSet class in Java is an implementation of the Tree data structure.
Press true if you believe the statement is correct, or false otherwise.
Generating complete for this lesson!
