Java Collection Exercise

The Java Collection framework is a fundamental part of the Java programming language, It covers a major part of Java and acts as a prerequisite for many Advanced Java Topics.

What is Collection in Java?

Collection Framework in Java contains a Set of Interfaces and Classes to represent groups of objects as a Single Unit. In Java, the Collection interface (java.util.Collection) and Map interface (java.util.Map) are the two main “root” interfaces of Java collection classes.

Basic Programs

Want to solidify your Java collection skills? Here's your chance! Get hands-on with these basic practice programs in Java Collection. Work with common collections like ArrayLists and HashSets, all while strengthening your Java coding abilities.

1. How to Print a Collection in Java?

import java.util.*;

class GFG {
    public static void main(String[] args)
    {
        String[] geeks = { "Rahul", "Utkarsh", "Shubham", "Neelam" };

        List<String> al = new ArrayList<String>();

        // adding elements of array to arrayList.
        Collections.addAll(al, geeks);
        System.out.println(al);
    }
}

[Rahul, Utkarsh, Shubham, Neelam]

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2. How to Make a Collection Read-Only in Java?

import java.util.Set;
import java.util.HashSet;
import java.util.Collections;

class GFG {
    public static void main(String[] args)
    {
        // Set of Integer
        Set<Integer> numbers = new HashSet<Integer>();

        // Set have 1 to 10 numbers
        for (int i = 1; i <= 5; i++) {
            numbers.add(i);
        }

        // print the integers
        numbers.stream().forEach(System.out::print);
        // Removing element from the list
        numbers.remove(5);

        System.out.println("\nAfter Performing Operation");
        numbers.stream().forEach(System.out::print);
        System.out.println("\nSet is also By Default Readable and Writable");

        // Now making Read-Only Set using unmodifiableSet() method.
        try {
            numbers = Collections.unmodifiableSet(numbers);

            // This line will generate an Exception
            numbers.remove(4);
        }
        catch (UnsupportedOperationException unsupportedOperationException) {
            System.out.println("Exceptions is " + unsupportedOperationException);
        }
        finally {
            System.out.println(numbers.contains(3));
            System.out.println("Now Set is Read-Only");
        }
    }
}

12345
After Performing Operation
1234
Set is also By Default Readable and Writable
Exceptions is java.lang.UnsupportedOperationException
true
Now Set is Read-Only

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3. Java Program to Compare Elements in a Collection.

Input : List = [3, 5, 18, 4, 6]
Output: Min value of our list : 3
Max value of our list : 18
Explanation: Comparison lead to result that the min of the list is 3 and max of list is 18. Similarly we can test for other Collections too.

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4. Java Program to Remove a Specific Element From a Collection

Input: ArrayList : [10, 20, 30, 1, 2]
Index: 1
Output: ArrayList : [10, 30, 1, 2]
Explanation: Removed element from index 1.

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5. How to Get a Size of Collection in Java?

Input: Linked_List: [geeks, for, geeks]
Output: 3
Explanation: As there are only 3 elements in the Collection So the value returned is 3.

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ArrayList Problems

ArrayList is a Collection which is the implementation of Dynamic Array Data Structure.

1. How to Add an Element in Java ArrayList?

Input: Number of Elements to be Added: 3
Elements to be Added : "A" , "B" , "C"
Output: list=[ A, B, C ]

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2. How to remove an element from ArrayList in Java?

Input: ArrayList = [10, 20, 30, 1, 2] index=1
Output: [10, 30, 1, 2]

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3. How to Replace an Element in Java ArrayList?

Input: ArrayList = [A, B, C, D]
index = 2
element =' E '
Output: [ A, B, E, D ]

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4. Java Program to Convert Array to ArrayList.

Input: arr = [ 2, 3, 4, 5, 8]
Output: ArrayList = [ 2, 3, 4, 5, 8]

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5. Comparing two ArrayList In Java

Input : ArrayList1 = [1, 2, 3, 4],
ArrayList2 = [4, 2, 3, 1]
Output: Array List are not equal

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LinkedList Problems

LinkedList Class is an implementation of the LinkedList data structure which is a linear data structure where the elements are not stored in contiguous locations and every element is a separate object with a data part and address part.

1. How to Iterate LinkedList in Java?

import java.util.Iterator; 
import java.util.LinkedList; 

public class GFG { 
    public static void main(String[] args) { 

        // Creating a LinkedList of Integer Type 
        LinkedList<Integer> linkedList = new LinkedList<>(); 

        // Inserting some Integer values to our LinkedList 
        linkedList.add(15); 
        linkedList.add(10); 
        linkedList.add(1); 
        linkedList.add(40); 
        linkedList.add(71); 

        // Calling the function to iterate our LinkedList 
        iterateUsingIterator(linkedList); 
    } 

    // Function to iterate the Linked List using Iterator 
    public static void iterateUsingIterator(LinkedList<Integer> linkedList){ 

        System.out.print("Iterating the LinkedList using Iterator : "); 

        // Creating an Iterator to our current LinkedList 
        Iterator it = linkedList.iterator(); 
        while(it.hasNext()){ 

            // next() return the next element in the iteration 
            System.out.print(it.next() + " "); 
        } 

    } 
} 

Iterating the LinkedList using Iterator : 15 10 1 40 71 

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2. How to Perform List to Set Conversion in Java?

Input: List : {1,2,3,4}
Output: Set : {1,2,3,4}

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3. Java Program to Convert ArrayList to LinkedList.

Input: ArrayList : {1,2,3,4}
Output: LinkedList : {1,2,3,4}

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4. Java Program to Convert Array to LinkedList in Java.

Input: Array : {1,2,3,4}
Output: LinkedList : {1,2,3,4}

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HashMap Problems

HashMap is the Class in Java Collection which is implemented based on Map Data Structure. It works on Key value pairs where we can store data in pairs , and can access based on Key values in Java.
 

1. How to Iterate HashMap in Java?

Input: { "A" = "Angular" , "P": "Python" , "J" = "Java" , "H" = "Hibernate" }
Output: P = Python
A = Angular
H = Hibernate
J = Java

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2. How to Check if a Key exists in a HashMap in Java?

Input: HashMap: { 1=Geeks, 2=ForGeeks, 3=GeeksForGeeks }, key = 2
Output: True
Input: HashMap: { 1=G, 2=e, 3=e, 4=k, 5=s }, key = 10
Output: False

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3. Java Program to Find the Occurrence of Words in a String using HashMap.

Input: "Alice is girl and Bob is boy"
Output: { Bob=1 , Alice=1 , and=1 , is=2 , girl=1 , boy=1 }

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4. How to Copy One HashMap to Another HashMap in Java?

Input: HashMap1 = { A=1 , B=2 , C=3 }
Output: HashMap2 = { A=1 , B=2 , C=3 }

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5. Java Program to Print all Duplicate characters in a String.

Input: str = "geeksforgeeks"
Output: s : 2
e : 4
g : 2
k : 2

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6. Java Program to Convert HashMap to TreeMap.

Input: HashMap: {1=Geeks, 2=forGeeks, 3=A computer Portal} 
Output: TreeMap: {1=Geeks, 2=forGeeks, 3=A computer Portal}

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HashSet Problems

Challenge your understanding of Java HashSets! This section dives into practical problems that test your ability to leverage the unique properties of HashSets. Solve these problems and solidify your grasp of this essential Java collection!

1. Initializing HashSet in Java

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2. How to Sort HashSet in Java.

Input: HashSet: [Geeks, For, ForGeeks, GeeksforGeeks]
Output: [For, ForGeeks, Geeks, GeeksforGeeks]

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3. Convert Array to HashSet in Java.

Input : Array: [1, 2, 3, 4, 5, 6]
Output: Set: [1, 2, 3, 4, 5, 6]

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4. How to Print HashSet Elements in Java?

Input: Set: { 5 , 2 , 3 , 6 , null };
Output: null
2
3
5
6
Explanation: Elements of Set are not stored in the order they are inserted.

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Stack Problems

Stack is part of Collection in Java, it is a class which extends Vector class. It follows the principle of LIFO that is Last in First Out.

1. How to Add Elements in Stack Collection in Java?

Input: stack = [10, 20, 30, 40, 50]
ele = 100
Output: [10 , 20 , 30 , 40 , 50, 100]
Explanation: Add element (ele) in the stack.

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2. Calculate weight of parenthesis based on the given conditions.

Input: S = “(()(()))” 
Output: 6 
Explanation: 
() = 1 , then (()) =2
()(()) = 1+2 = 3
(()(())) = 2*3 = 6

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3. Check If it is Possible to Convert Binary String into Unary String

Choose two adjacent characters, such that both are 1’s or 0’s. Then invert them, Formally, if both are 0’s then into 1’s or vice-versa. 
If we are able to convert every element either to all 1 or all 0 then the answer will be Yes else No.
Input: N = 6, S = “110110”
Output: YES
Explanation: The operations are performed as:
Invert 0,1 -> S = 000110
Invert 4,5 -> S = 000000

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Queue Problems

Queue is the part of Java Collection, it is an Interface based on Queue Data Structure. It follows the Principle of FIFO that is First In First Out. 
 

1. How to Iterate over a Queue in Java?

Below is the Solution of the question:

import java.util.Iterator; 
import java.util.LinkedList; 
import java.util.Queue; 

public class Gfg { 
    public static void main(String[] args) { 
        
        // Iterating Queue 
        Queue<Integer> studentQueue = new LinkedList<>(); 

        // Inserting element in Queue 
        studentQueue.add(1); 
        studentQueue.add(3); 
        studentQueue.add(8); 
        studentQueue.add(14);         
        studentQueue.add(9);         
        studentQueue.add(3);         
        
        // Initialising Iterator 
        Iterator<Integer> studentQueueIterator = studentQueue.iterator(); 
        
        // Iterating Queue 
        while (studentQueueIterator.hasNext()) { 
            Integer name = studentQueueIterator.next(); 
            System.out.print(name+" "); 
        } 
    } 
} 

1 3 8 14 9 3 

2. How to Add Elements in Queue Collection in Java?

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3. How to Implement a Circular Queue in Java?

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4. How to Convert a List to a Queue in Java?

Input: List = { A, B, C}
Output: Queue = { A, B, C }

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Priority Queue Problems

Got the hang of Java collections? Time to test your skills! This section throws some priority queue problems your way. Practice putting elements in order, taking them out strategically, and mastering this awesome data structure in a fun way.
 

1. How to implement Min Heap in Java?

Input: 5 , 1 , 10 , 30 , 20
Output: 1 , 5, 10 , 20 , 30
Explanation: Min Heap is a type of Data Structure in which internal node is smaller than or equal to its children.

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2. How to Configure Java Priority Queue to Handle Duplicate Elements?

PriorityQueue doesn't handle duplicate elements in a specific way. But we can configure PriorityQueue to add add duplicate elements in it.

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3. How to Check if a PriorityQueue is Empty or Contains Elements in Java?

Input: { 6 , 4 , 1 , 55 }
Output: Not Empty

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4. How to Implement PriorityQueue through Comparator in Java?

Implementation of a PriorityQueue Using a Custom Comparator to Define the Priority of Elements in the Queue.

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5. Java Program to Sort Items By Weight

Input: items = [“Laptop”, “TV”, “Phone”, “Watch”]
weights = [500, 1000,250, 50]
Output: [“TV”, “Laptop”, “Phone”, “Watch”]
Explanation: Here the items are sorted based on their weight in decreasing order

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