Map, Stacks & Collections

#Java

Coleções, Map, Stack: Resumo

List ↔ Lista

Nome: Lista
Descrição: É uma coleção ordenada de elementos (índices começam em zero). Permitem duplicata.
Implementações incluem ArrayList, LinkedList, Vector e outras.
Operações típicas incluem adicionar, remover e acessar itens por índice.

Set ↔ Conjunto

Nome: Conjunto
Descrição: É uma coleção de elementos únicos (sem duplicatas). Sem ordem específica.
Implementações incluem HashSet, TreeSet (ordenado por chave) e LinkedHashSet (manter a ordem adicionada ou percorrida).
Operações típicas incluem adicionar, remover e verificar se um elemento está presente.

Queue ↔ Fila

Nome: Fila
Descrição: É uma coleção que segue o princípio First-In-First-Out (FIFO). Permitem duplicata.
Implementações incluem LinkedList (implementação padrão) e ArrayDeque.
Operações típicas incluem adicionar elementos, remover um elemento (poll), verificar se a fila está vazia, e olhar para o início da fila.

Deque

Nome: Deque
Descrição: É uma coleção duplamente encadeada com métodos para adicionar ou remover itens de ambos os lados (à frente e atrás). Permitem duplicata.
Implementações incluem ArrayDeque e LinkedList.
Operações típicas incluem adicionar elementos, remover um elemento do front (pollFirst), remover um elemento do final (pollLast), verificar se a fila está vazia ou se o tamanho é zero.

Stack ↔ Pilha

Nome: Pilha
Descrição: É uma coleção de último em primeiro (LIFO) com métodos para adicionar e remover itens apenas do final (topo). Permitem duplicata.
Implementações incluem Stack (implementação padrão usando Vector) e ArrayDeque.
Operações típicas incluem adicionar um elemento, remover o topo mais recente (pop), verificar se a pilha está vazia, e olhar para o topo da pilha.

Map ↔ Mapa

Nome: Mapa
Descrição: É uma associação de chaves com valores. As chaves são únicas, mas vários valores podem ser associados a uma mesma chave.
Implementações incluem HashMap, TreeMap (ordenado por chave) e LinkedHashMap (mantém a ordem adicionada ou percorrida).
Operações típicas incluem adicionar pares de chaves-valores, remover pares de chaves-valores, recuperar valores por chave, verificar se uma chave está presente e iterar sobre as chaves ou valores.

Exemplos:

1) Lista:

// Java program to Demonstrate List Interface

// Importing all utility classes

import java.util.*;

// Main class

// ListDemo class

class GFG {

// Main driver method

public static void main(String[] args)

{

// Creating an object of List interface

// implemented by the ArrayList class

List<Integer> l1 = new ArrayList<Integer>();

// Adding elements to object of List interface

// Custom inputs

l1.add(0, 1);

l1.add(1, 2);

// Print the elements inside the object

System.out.println(l1);

// Now creating another object of the List

// interface implemented ArrayList class

// Declaring object of integer type

List<Integer> l2 = new ArrayList<Integer>();

// Again adding elements to object of List interface

// Custom inputs

l2.add(1);

l2.add(2);

l2.add(3);

// Will add list l2 from 1 index

l1.addAll(1, l2);

System.out.println(l1);

// Removes element from index 1

l1.remove(1);

// Printing the updated List 1

System.out.println(l1);

// Prints element at index 3 in list 1

// using get() method

System.out.println(l1.get(3));

// Replace 0th element with 5

// in List 1

l1.set(0, 5);

// Again printing the updated List 1

System.out.println(l1);

}

// Java Program to Add Elements to a List

// Importing all utility classes

import java.util.*;

// Main class

class GFG {

// Main driver method

public static void main(String args[])

{

// Creating an object of List interface,

// implemented by ArrayList class

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

// Adding elements to object of List interface

// Custom elements

al.add("Geeks");

al.add(1, "For");

// Print all the elements inside the

// List interface object

System.out.println(al);

}

################################################################################

2) Set

// Java program Illustrating Set Interface

// Importing utility classes

import java.util.*;

// Main class

public class GFG {

// Main driver method

public static void main(String[] args)

{

// Demonstrating Set using HashSet

// Declaring object of type String

Set<String> hash_Set = new HashSet<String>();

// Adding elements to the Set

// using add() method

hash_Set.add("Geeks");

hash_Set.add("For");

hash_Set.add("Geeks");

hash_Set.add("Example");

hash_Set.add("Set");

// Printing elements of HashSet object

System.out.println(hash_Set);

}

// Java Program Demonstrating Operations on the Set

// such as Union, Intersection and Difference operations

// Importing all utility classes

import java.util.*;

// Main class

public class SetExample {

// Main driver method

public static void main(String args[])

{

// Creating an object of Set class

// Declaring object of Integer type

Set<Integer> a = new HashSet<Integer>();

// Adding all elements to List

a.addAll(Arrays.asList(

new Integer[] { 1, 3, 2, 4, 8, 9, 0 }));

// Again declaring object of Set class

// with reference to HashSet

Set<Integer> b = new HashSet<Integer>();

b.addAll(Arrays.asList(

new Integer[] { 1, 3, 7, 5, 4, 0, 7, 5 }));

// To find union

Set<Integer> union = new HashSet<Integer>(a);

union.addAll(b);

System.out.print("Union of the two Set");

System.out.println(union);

// To find intersection

Set<Integer> intersection = new HashSet<Integer>(a);

intersection.retainAll(b);

System.out.print("Intersection of the two Set");

System.out.println(intersection);

// To find the symmetric difference

Set<Integer> difference = new HashSet<Integer>(a);

difference.removeAll(b);

System.out.print("Difference of the two Set");

System.out.println(difference);

}

################################################################################

3) Queue:

import java.util.LinkedList;

import java.util.Queue;

public class QueueExample {

public static void main(String[] args) {

Queue<String> queue = new LinkedList<>();

// add elements to the queue

queue.add("apple");

queue.add("banana");

queue.add("cherry");

// print the queue

System.out.println("Queue: " + queue);

// remove the element at the front of the queue

String front = queue.remove();

System.out.println("Removed element: " + front);

// print the updated queue

System.out.println("Queue after removal: " + queue);

// add another element to the queue

queue.add("date");

// peek at the element at the front of the queue

String peeked = queue.peek();

System.out.println("Peeked element: " + peeked);

// print the updated queue

System.out.println("Queue after peek: " + queue);

}

// Java program to demonstrate a Queue

import java.util.LinkedList;

import java.util.Queue;

public class QueueExample {

public static void main(String[] args)

{

Queue<Integer> q

= new LinkedList<>();

// Adds elements {0, 1, 2, 3, 4} to

// the queue

for (int i = 0; i < 5; i++)

q.add(i);

// Display contents of the queue.

System.out.println("Elements of queue "

+ q);

// To remove the head of queue.

int removedele = q.remove();

System.out.println("removed element-"

+ removedele);

System.out.println(q);

// To view the head of queue

int head = q.peek();

System.out.println("head of queue-"

+ head);

// Rest all methods of collection

// interface like size and contains

// can be used with this

// implementation.

int size = q.size();

System.out.println("Size of queue-"

+ size);

}

################################################################################

4) Deque

import java.util.ArrayDeque;

import java.util.Deque;

public class Example {

public static void main(String[] args) {

Deque<Integer> deque = new ArrayDeque<>();

deque.addFirst(1);

deque.addLast(2);

int first = deque.removeFirst();

int last = deque.removeLast();

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

}

// Java program to demonstrate the working

// of a Deque in Java

import java.util.*;

public class DequeExample {

public static void main(String[] args)

{

Deque<String> deque

= new LinkedList<String>();

// We can add elements to the queue

// in various ways

// Add at the last

deque.add("Element 1 (Tail)");

// Add at the first

deque.addFirst("Element 2 (Head)");

// Add at the last

deque.addLast("Element 3 (Tail)");

// Add at the first

deque.push("Element 4 (Head)");

// Add at the last

deque.offer("Element 5 (Tail)");

// Add at the first

deque.offerFirst("Element 6 (Head)");

System.out.println(deque + "\n");

// We can remove the first element

// or the last element.

deque.removeFirst();

deque.removeLast();

System.out.println("Deque after removing "

+ "first and last: "

+ deque);

}

################################################################################

5) Stack:

// Java code for stack implementation

import java.io.*;

import java.util.*;

class Test

{

// Pushing element on the top of the stack

static void stack_push(Stack<Integer> stack)

{

for(int i = 0; i < 5; i++)

{

stack.push(i);

}

// Popping element from the top of the stack

static void stack_pop(Stack<Integer> stack)

{

System.out.println("Pop Operation:");

for(int i = 0; i < 5; i++)

{

Integer y = (Integer) stack.pop();

System.out.println(y);

}

// Displaying element on the top of the stack

static void stack_peek(Stack<Integer> stack)

{

Integer element = (Integer) stack.peek();

System.out.println("Element on stack top: " + element);

}

// Searching element in the stack

static void stack_search(Stack<Integer> stack, int element)

{

Integer pos = (Integer) stack.search(element);

if(pos == -1)

System.out.println("Element not found");

else

System.out.println("Element is found at position: " + pos);

}

public static void main (String[] args)

{

Stack<Integer> stack = new Stack<Integer>();

stack_push(stack);

stack_pop(stack);

stack_push(stack);

stack_peek(stack);

stack_search(stack, 2);

stack_search(stack, 6);

}

// Java program to add the

// elements in the stack

import java.io.*;

import java.util.*;

class StackDemo {

// Main Method

public static void main(String[] args)

{

// Default initialization of Stack

Stack stack1 = new Stack();

// Initialization of Stack

// using Generics

Stack<String> stack2 = new Stack<String>();

// pushing the elements

stack1.push("4");

stack1.push("All");

stack1.push("Geeks");

stack2.push("Geeks");

stack2.push("For");

stack2.push("Geeks");

// Printing the Stack Elements

System.out.println(stack1);

System.out.println(stack2);

}

################################################################################

6) Map:

// Java Program to Demonstrate

// Working of Map interface

// Importing required classes

import java.util.*;

// Main class

class GFG {

// Main driver method

public static void main(String args[])

{

// Creating an empty HashMap

Map<String, Integer> hm

= new HashMap<String, Integer>();

// Inserting pairs in above Map

// using put() method

hm.put("a", new Integer(100));

hm.put("b", new Integer(200));

hm.put("c", new Integer(300));

hm.put("d", new Integer(400));

// Traversing through Map using for-each loop

for (Map.Entry<String, Integer> me :

hm.entrySet()) {

// Printing keys

System.out.print(me.getKey() + ":");

System.out.println(me.getValue());

}

// Java Program to illustrate the Hashmap Class

// Importing required classes

import java.util.*;

// Main class

public class GFG {

// Main driver method

public static void main(String[] args)

{

// Creating an empty HashMap

Map<String, Integer> map = new HashMap<>();

// Inserting entries in the Map

// using put() method

map.put("vishal", 10);

map.put("sachin", 30);

map.put("vaibhav", 20);

// Iterating over Map

for (Map.Entry<String, Integer> e : map.entrySet())

// Printing key-value pairs

System.out.println(e.getKey() + " "

+ e.getValue());

}

Exemplos de referência:

https://www.geeksforgeeks.org/collections-in-java-2/

Mais exemplos:

https://github.com/claudio-es-andrade/Artigos/Collections