HashMap em Java
Na discussão de hoje, abordaremos o Java HashMap com exemplos , que se destinam a atender às necessidades de aprendizado de nossos alunos
Java HashMap
Você aprendeu no capítulo ArrayList que os arrays contêm itens em uma coleção ordenada que pode ser acessada por números de índice ( ints ).
No que diz respeito aos Java HashMaps , o Hashmap armazena os itens em grupos de pares “ chave/valor ” e você pode acessá-los por um tipo de dados de índice em vez de usar apenas int (por exemplo, String ).
A chave (índice) de um objeto é usada para acessar o valor de outro objeto.
Existem dois tipos de dados que ele pode armazenar: chaves de string e valores de caractere, ou o mesmo tipo, como chaves de string e valores de string.
Crie um objeto HashMap e nomeie-o como sports_players para armazenar chaves de String e valores de String :
import java.util.HashMap; // HashMap class is imported here
HashMap<String, String> sports_players = new HashMap<String, String>();
Crie um objeto HashMap e nomeie-o como rank_Id para armazenar chaves de String e valores de String:
import java.util.HashMap; // HashMap class is imported here
HashMap<Integer, Integer> rank_Id = new HashMap<Integer, Integer>();
Índice-
Java HashMap Put()
Existem muitos métodos úteis na classe HashMap . Você pode usar o método put() para adicionar itens a ele, por exemplo:
Declare um objeto HashMap e nomeie-o como sports_players para armazenar chaves de string como nome de esportes e valores de string como nome de jogador famoso.
Example:
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123456789101112131415161718192021import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<String, String> sports_players = new HashMap<String, String>(); // The object of Hashmap is created heere in which key and value both are of type String. sports_players.put("Football","Cristiano Ronaldo"); sports_players.put("Cricket","Sachin Tendulkar"); sports_players.put("Hockey","Wayne Gretzky"); sports_players.put("Baseball","Babe Ruth"); sports_players.put("Rugby","Jonah Lomu"); System.out.println(sports_players); }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Da mesma forma, inicializamos um objeto HashTree que armazena classificação como chaves e Id como valor:
Example:
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12345678910111213141516171819202122import java.util.HashMap; // HashMap class is imported here public class Main { public static void main(String[] args) { HashMap<Integer, Integer> rank_Id = new HashMap<Integer, Integer>();// Here, a HashMap object is created and named as rank_Id, whose key and value are both integers. rank_Id.put(1,10001); rank_Id.put(2,10002); rank_Id.put(3,10003); rank_Id.put(4,10004); rank_Id.put(5,10005); System.out.println(rank_Id); }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Java HashMap Get()
Quando discutimos Java HashMap , o método get() e a chave são usados para acessar valores em um HashMap.
Example:
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12345678910111213141516171819202122232425262728import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<String, String> it_Firms = new HashMap<String,String >(); it_Firms.put("1","Cognizant"); it_Firms.put("2","Vates-Software"); it_Firms.put("3","MantorMate"); it_Firms.put("4","Resultant"); it_Firms.put("5","Fortegrp"); // All Elements of HashMap System.out.println(it_Firms); // By accessing the value at key number 3 System.out.println("\nValue at key 3: "+it_Firms.get("3")); }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Outra Abordagem:
Example:
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12345678910111213141516171819202122232425262728import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<Integer,Integer> rank_Age = new HashMap<Integer,Integer>(); rank_Age.put(1,21); rank_Age.put(2,25); rank_Age.put(3,31); rank_Age.put(4,41); rank_Age.put(5,37); // All Elements of HashMap System.out.println(rank_Age); // By accessing the Age at key number 2 System.out.println("\nValue at key 2: "+rank_Age.get(2)); }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Java HashMap Remove()
Usando o método remove() , remova um item referenciando sua chave.
O exemplo abaixo mostra a remoção de Key (“ Team 4 ”) avaliado como Cleveland Cavaliers.
Hashmap remove Example: 1
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12345678910111213141516171819202122232425262728293031323334import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<String,String> nba_Teams = new HashMap<String,String>(); nba_Teams.put("Team 1"," Boston Celtics"); nba_Teams.put("Team 2"," Chicago Bulls"); nba_Teams.put("Team 3"," Atlanta Hawks"); nba_Teams.put("Team 4"," Cleveland Cavaliers"); nba_Teams.put("Team 5"," Detroit Pistons"); // Here we print all Elements of the HashMap Object named as nba_Teams before removing an item System.out.println("\nBefore Removing Value: "+nba_Teams); // Removing Cleveland Cavaliers by using its key (Team 4) String removed= nba_Teams.remove("Team 4"); System.out.println("\nRemoved Value is: "+removed); // Printing all elements of HashMap after an element was removed: System.out.println("\nAfter Removing value: "+nba_Teams); }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Example: 2
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1234567891011121314151617181920212223242526272829303132333435import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<Float,Float> person_Id_Height = new HashMap<Float,Float>(); person_Id_Height.put(10f,5.4f); person_Id_Height.put(20f,5.6f); person_Id_Height.put(30f,5.7f); person_Id_Height.put(40f,6.2f); person_Id_Height.put(50f,5.11f); // Here we print all Elements of the HashMap Object named as person_Id_Height before the item is element System.out.println("\nBefore Removing Value: "+person_Id_Height); // Removing from person_Id_Height HashMap by using its key (40f) float removed= person_Id_Height.remove(40f); System.out.println("\nRemoved Value is: "+removed); // Printing all elements of HashMap after an element was removed: System.out.println("\nAfter Removing value: "+person_Id_Height); }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Usando o método clear() , você pode remover todos os itens do objeto HashMap:
Example:
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123456789101112131415161718192021222324252627282930313233import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<String,String> product_code = new HashMap<String,String>(); product_code.put("Cookies","102313"); product_code.put("Biscuits","153532"); product_code.put("Snacks","632123"); product_code.put("PopCorns","361232"); product_code.put("Chocolates","734231"); // Here we print all Elements of the HashMap Object named as product_code System.out.println("HashMap: "+product_code); // After using .clear() method our HashMap becomes empty product_code.clear(); // Printing all elements of HashMap after all elements were removed: System.out.println("After clearing the HashMap we get: "+product_code); }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Aqui limpamos todo o HashMap usando o método clear() :
Example:
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1234567891011121314151617181920212223242526272829303132import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<Float,Float> results_division_ = new HashMap<Float,Float>(); results_division_.put(14f/5f,2.8f); results_division_.put(18f/7f,2.57f); results_division_.put(19f/4f,4.75f); results_division_.put(11f/3f,3.66f); // Here we print all Elements of the HashMap Object named as results_division_ System.out.println("HashMap: "+results_division_); // After using .clear() method our HashMap becomes empty results_division_.clear(); // Printing all elements of HashMap after all elements were removed: System.out.println("After clearing the HashMap we get: "+results_division_); }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Tamanho do HashMap
O método size() pode ser usado para descobrir quantos itens existem no HashMap:
Example:
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12345678910111213141516171819202122232425262728import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<String,String> rank_billionaires_name = new HashMap<String,String>(); rank_billionaires_name.put("Rank 1: "," Bernard Arnault & family"); rank_billionaires_name.put("Rank 2: "," Elon Musk"); rank_billionaires_name.put("Rank 3: "," Gautam Adani"); rank_billionaires_name.put("Rank 4: "," Jeff Bezos"); // Here we print all Elements of the HashMap Object named as rank_billionaires_name System.out.println("HashMap: "+rank_billionaires_name); // By using size() method we can determine the size of our HashMap System.out.println("\nSize of HashMap: "+rank_billionaires_name.size()); }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Example:
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12345678910111213141516171819202122232425262728import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<Character,Character> vowels_List = new HashMap<Character,Character>(); vowels_List.put('a','A'); vowels_List.put('e','E'); vowels_List.put('i','I'); vowels_List.put('o','O'); vowels_List.put('u','U'); // Here we print all Elements of the HashMap Object named as vowels_List System.out.println("Vowels HashMap: "+vowels_List); // By using size() method we can determine the size of our HashMap System.out.println("\nSize of HashMap: "+vowels_List.size()); }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Percorrer um HashMap
Um loop for-each percorre os itens de um HashMap.
Lembre-se: Se você quiser apenas as chaves, use o método keySet() e, se quiser apenas os valores, use o método values() .
Os exemplos a seguir mostram como podemos imprimir todas as chaves do HashMap usando o método keySet() :
Example: 1
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123456789101112131415161718192021222324252627import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<String, String> it_Firms = new HashMap<String,String >(); it_Firms.put("1","Cognizant"); it_Firms.put("2","Vates-Software"); it_Firms.put("3","MantorMate"); it_Firms.put("4","Resultant"); it_Firms.put("5","Fortegrp"); // Using for-each loop to traverse through the keys of HashMap object named it_Firms for(String mrx:it_Firms.keySet()){ System.out.println(mrx); } }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Example:2
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1234567891011121314151617181920212223242526import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<Integer,Integer> odd_Even = new HashMap<Integer,Integer>(); odd_Even.put(1,2); odd_Even.put(3,4); odd_Even.put(5,6); odd_Even.put(7,8); odd_Even.put(9,10); // Using for-each loop to print through the keys of HashMap object named odd_Even for(Integer ample:odd_Even.keySet()){ System.out.println(ample); } }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Da mesma forma, também podemos percorrer e imprimir os valores do HashMap usando o método values() :
Example:3
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123456789101112131415161718192021222324252627import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<String, String> it_Firms = new HashMap<String,String >(); it_Firms.put("1","Cognizant"); it_Firms.put("2","Vates-Software"); it_Firms.put("3","MantorMate"); it_Firms.put("4","Resultant"); it_Firms.put("5","Fortegrp"); // Using for-each loop to print the values of HashMap object named it_Firms using the values() method for(String ample:it_Firms.values()){ System.out.println(ample); } }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Imprimimos as chaves e valores do objeto nomeado como odd_Even do HashMap:
Example:4
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1234567891011121314151617181920212223242526import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<Integer,Integer> odd_Even = new HashMap<Integer,Integer>(); odd_Even.put(1,2); odd_Even.put(3,4); odd_Even.put(5,6); odd_Even.put(7,8); odd_Even.put(9,10); // Using for-each loop to print all the values of HashMap object named odd_Even using the values() method for(Integer ample:odd_Even.values()){ System.out.println(ample); } }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Da mesma forma, também podemos imprimir ambos ( Chaves e valores ) de uma vez usando o método keySet() e o método get() :
Example:5
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12345678910111213141516171819202122232425262728import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<String, String> it_Firms = new HashMap<String,String >(); it_Firms.put("1","Cognizant"); it_Firms.put("2","Vates-Software"); it_Firms.put("3","MantorMate"); it_Firms.put("4","Resultant"); it_Firms.put("5","Fortegrp"); // We can also access the keys and values at a time for(String ample:it_Firms.keySet()){ System.out.println("Key: "+ample+" Value: "+it_Firms.get(ample)); } }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Example:6
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1234567891011121314151617181920212223242526import java.util.HashMap; // HashMap class is imported herepublic class Main { public static void main(String[] args) { HashMap<Integer,Integer> odd_Even = new HashMap<Integer,Integer>(); odd_Even.put(1,2); odd_Even.put(3,4); odd_Even.put(5,6); odd_Even.put(7,8); odd_Even.put(9,10); // As we did in the example above, we can print the keys and the values at a same time using th for-each loop for(Integer mrx:odd_Even.keySet()){ System.out.println("Key Number: "+mrx+" Value: "+odd_Even.get(mrx)); } }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Outros tipos
Na verdade, existem objetos que compõem as chaves e os valores de um HashMap. Objetos do tipo “ String ” e “Integer” foram usados nos exemplos acima. Strings são objetos em Java (não tipos primitivos).
Se quiser acessar outros tipos , como int , você precisará especificar uma classe wrapper equivalente: Integer.
Quando se trata de outros tipos primitivos , use Boolean para boolean, caractere para caractere, double para double, etc.
Para armazenar chaves Integer e valores String , criamos um objeto HashMap chamado silent_letter_words:
Example:
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12345678910111213141516171819202122232425import java.util.HashMap;public class Main { public static void main(String[] args) { HashMap <Integer,String> silent_letter_words=new HashMap<Integer,String>(); silent_letter_words.put(1,"Bomb"); silent_letter_words.put(2,"Knife"); silent_letter_words.put(3,"Kitchen"); silent_letter_words.put(4,"Wrap"); silent_letter_words.put(5,"Cupboard"); for(int mrx:silent_letter_words.keySet()){ System.out.println("Number "+mrx+" ="+" Word: "+silent_letter_words.get(mrx)); } }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Além disso, também podemos imprimir o nome das pessoas como chaves e seus pesos corporais como valor , conforme mostrado abaixo:
Example:
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12345678910111213141516171819202122232425import java.util.HashMap;public class Main { public static void main(String[] args) { HashMap <String,Double> person_Weight=new HashMap<String,Double>(); person_Weight.put("Joseph",56.8d); person_Weight.put("Diana",64.2d); person_Weight.put("Emma",44.1d); person_Weight.put("Sophia",77.4d); person_Weight.put("Noah",58.9d); for(String ample:person_Weight.keySet()){ System.out.println(ample+" have "+"Weight= "+person_Weight.get(ample)+" kgs"); } }}XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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