A Complete Guide - Java Programming ArrayList, LinkedList, HashSet, TreeSet, HashMap, TreeMap

1. ArrayList

Step-by-Step Example:

Step 1: Import the ArrayList class

First, you need to import the ArrayList class from the java.util package.

import java.util.ArrayList;

Step 2: Create an ArrayList object

Create an instance of the ArrayList class. Typically, you specify the type of elements it will hold using generics.

public class ArrayListExample {
    public static void main(String[] args) {
        // Create an ArrayList to store Strings
        ArrayList<String> arrayList = new ArrayList<>();

        // Adding elements to the ArrayList
        arrayList.add("Apple");
        arrayList.add("Banana");
        arrayList.add("Cherry");

        // Displaying elements of the ArrayList
        System.out.println("ArrayList: " + arrayList);
    }
}

Step 3: Access, modify, and remove elements

You can access, modify, and remove elements in an ArrayList.

// Accessing elements by index
String fruit = arrayList.get(1);  // Get the fruit at index 1 (Banana)
System.out.println("Fruit at index 1: " + fruit);

// Modifying elements by index
arrayList.set(1, "Blueberry");  // Change the fruit at index 1 to Blueberry
System.out.println("ArrayList after modification: " + arrayList);

// Removing elements by index or value
arrayList.remove(0);  // Remove the element at index 0 (Apple)
arrayList.remove("Cherry");  // Remove Cherry directly
System.out.println("ArrayList after removal: " + arrayList);

2. LinkedList

Step-by-Step Example:

Step 1: Import the LinkedList class

import java.util.LinkedList;

Step 2: Create a LinkedList object

public class LinkedListExample {
    public static void main(String[] args) {
        // Create a LinkedList to store Strings
        LinkedList<String> linkedList = new LinkedList<>();

        // Adding elements to the LinkedList
        linkedList.add("Dog");
        linkedList.add("Cat");
        linkedList.add("Bird");

        // Displaying elements of the LinkedList
        System.out.println("LinkedList: " + linkedList);
    }
}

Step 3: Access, modify, and remove elements

// Accessing elements by index
String animal = linkedList.get(1);  // Get the animal at index 1 (Cat)
System.out.println("Animal at index 1: " + animal);

// Modifying elements by index
linkedList.set(1, "Fox");  // Change the animal at index 1 to Fox
System.out.println("LinkedList after modification: " + linkedList);

// Removing elements by index or value
linkedList.remove(0);  // Remove the element at index 0 (Dog)
linkedList.remove("Bird");  // Remove Bird directly
System.out.println("LinkedList after removal: " + linkedList);

3. HashSet

Step-by-Step Example:

Step 1: Import the HashSet class

import java.util.HashSet;

Step 2: Create a HashSet object

public class HashSetExample {
    public static void main(String[] args) {
        // Create a HashSet to store Strings
        HashSet<String> hashSet = new HashSet<>();

        // Adding elements to the HashSet
        hashSet.add("Red");
        hashSet.add("Green");
        hashSet.add("Blue");

        // Displaying elements of the HashSet
        System.out.println("HashSet: " + hashSet);
    }
}

Note: Elements are stored in no particular order. Also, HashSet does not allow duplicate elements.

Step 3: Check for existence and remove elements

// Checking if an element exists in the HashSet
boolean containsGreen = hashSet.contains("Green");
System.out.println("Contains Green: " + containsGreen);

// Removing elements from the HashSet
hashSet.remove("Blue");  // Remove Blue directly
System.out.println("HashSet after removal: " + hashSet);

4. TreeSet

Step-by-Step Example:

Step 1: Import the TreeSet class

import java.util.TreeSet;

Step 2: Create a TreeSet object

public class TreeSetExample {
    public static void main(String[] args) {
        // Create a TreeSet to store Integers
        TreeSet<Integer> treeSet = new TreeSet<>();

        // Adding elements to the TreeSet
        treeSet.add(5);
        treeSet.add(3);
        treeSet.add(8);

        // Displaying elements of the TreeSet
        System.out.println("TreeSet: " + treeSet);
    }
}

Note: Elements in TreeSet are stored in sorted order, and no duplicates.

Step 3: Perform operations like navigation to first and last element

// Accessing the first and last element in the TreeSet
int first = treeSet.first();  // Get the smallest element (3)
int last = treeSet.last();  // Get the largest element (8)

System.out.println("First element: " + first);
System.out.println("Last element: " + last);

// Removing elements from the TreeSet
treeSet.remove(5);  // Remove 5 directly
System.out.println("TreeSet after removal: " + treeSet);

// Additional: Navigating elements
Integer lower = treeSet.lower(8);  // Get the largest element less than 8 (3)
Integer higher = treeSet.higher(3);  // Get the smallest element greater than 3 (8)

System.out.println("Lower element of 8: " + lower);
System.out.println("Higher element of 3: " + higher);

5. HashMap

Step-by-Step Example:

Step 1: Import the HashMap class

import java.util.HashMap;

Step 2: Create a HashMap object

public class HashMapExample {
    public static void main(String[] args) {
        // Create a HashMap to store (String, Integer) key-value pairs
        HashMap<String, Integer> hashMap = new HashMap<>();

        // Adding key-value pairs to the HashMap
        hashMap.put("Alice", 25);
        hashMap.put("Bob", 30);
        hashMap.put("Charlie", 35);

        // Displaying key-value pairs of the HashMap
        System.out.println("HashMap: " + hashMap);
    }
}

Step 3: Access, modify, and remove key-values

// Accessing the value of a key in the HashMap
int aliceAge = hashMap.get("Alice");
System.out.println("Alice's Age: " + aliceAge);

// Modifying the value of a key in the HashMap
hashMap.put("Alice", 26);  // Change Alice's age to 26
System.out.println("HashMap after modification: " + hashMap);

// Removing a key-value pair from the HashMap
hashMap.remove("Bob");  // Remove Bob's entry directly
System.out.println("HashMap after removal: " + hashMap);

6. TreeMap

Step-by-Step Example:

Step 1: Import the TreeMap class

import java.util.TreeMap;

Step 2: Create a TreeMap object

public class TreeMapExample {
    public static void main(String[] args) {
        // Create a TreeMap to store (Integer, String) key-value pairs
        TreeMap<Integer, String> treeMap = new TreeMap<>();

        // Adding key-value pairs to the TreeMap
        treeMap.put(10, "Ten");
        treeMap.put(5, "Five");
        treeMap.put(20, "Twenty");

        // Displaying key-value pairs of the TreeMap
        System.out.println("TreeMap: " + treeMap);
    }
}

Note: Keys in TreeMap are stored in sorted order, and no duplicate keys are allowed. The values can be duplicate though.

Step 3: Access, modify, and remove key-values