Neste tutorial, aprenderemos sobre a classe Java TreeMap e suas operações com a ajuda de exemplos.
A TreeMapclasse da estrutura de coleções Java fornece a implementação da estrutura de dados em árvore.
Ele implementa a interface NavigableMap.
Criando um TreeMap
Para criar um TreeMap, devemos java.util.TreeMapprimeiro importar o pacote. Depois de importar o pacote, aqui está como podemos criar um TreeMapem Java.
TreeMap numbers = new TreeMap();
No código acima, criamos um TreeMapnúmero nomeado sem nenhum argumento. Nesse caso, os elementos em TreeMapsão classificados naturalmente (ordem crescente).
No entanto, podemos personalizar a classificação dos elementos usando a Comparatorinterface. Aprenderemos sobre isso posteriormente neste tutorial.
Aqui,
- Chave - um identificador único usado para associar cada elemento (valor) em um mapa
- Valor - elementos associados por chaves em um mapa
Métodos de TreeMap
A TreeMapclasse fornece vários métodos que nos permitem realizar operações no mapa.
Inserir elementos no TreeMap
put()- insere o mapeamento de chave / valor especificado (entrada) no mapaputAll()- insere todas as entradas do mapa especificado neste mapaputIfAbsent()- insere o mapeamento de chave / valor especificado no mapa se a chave especificada não estiver presente no mapa
Por exemplo,
import java.util.TreeMap; class Main ( public static void main(String() args) ( // Creating TreeMap of even numbers TreeMap evenNumbers = new TreeMap(); // Using put() evenNumbers.put("Two", 2); evenNumbers.put("Four", 4); // Using putIfAbsent() evenNumbers.putIfAbsent("Six", 6); System.out.println("TreeMap of even numbers: " + evenNumbers); //Creating TreeMap of numbers TreeMap numbers = new TreeMap(); numbers.put("One", 1); // Using putAll() numbers.putAll(evenNumbers); System.out.println("TreeMap of numbers: " + numbers); ) )
Resultado
TreeMap de números pares: (Four = 4, Six = 6, Two = 2) TreeMap de números: (Four = 4, One = 1, Six = 6, Two = 2)
Acessar elementos de TreeMap
1. Usando entrySet (), keySet () e values ()
entrySet()- retorna um conjunto de todos os mapeamentos de chave / valores (entrada) de um mapa de árvorekeySet()- retorna um conjunto de todas as chaves de um mapa de árvorevalues()- retorna um conjunto de todos os mapas de um mapa de árvore
Por exemplo,
import java.util.TreeMap; class Main ( public static void main(String() args) ( TreeMap numbers = new TreeMap(); numbers.put("One", 1); numbers.put("Two", 2); numbers.put("Three", 3); System.out.println("TreeMap: " + numbers); // Using entrySet() System.out.println("Key/Value mappings: " + numbers.entrySet()); // Using keySet() System.out.println("Keys: " + numbers.keySet()); // Using values() System.out.println("Values: " + numbers.values()); ) )
Resultado
TreeMap: (One = 1, Three = 3, Two = 2) Mapeamentos de chave / valor: (One = 1, Three = 3, Two = 2) Chaves: (One, Three, Two) Valores: (1, 3, 2 )
2. Usando get () e getOrDefault ()
get()- Retorna o valor associado à chave especificada. Retorna nulo se a chave não for encontrada.getOrDefault()- Retorna o valor associado à chave especificada. Retorna o valor padrão especificado se a chave não for encontrada.
Por exemplo,
import java.util.TreeMap; class Main ( public static void main(String() args) ( TreeMap numbers = new TreeMap(); numbers.put("One", 1); numbers.put("Two", 2); numbers.put("Three", 3); System.out.println("TreeMap: " + numbers); // Using get() int value1 = numbers.get("Three"); System.out.println("Using get(): " + value1); // Using getOrDefault() int value2 = numbers.getOrDefault("Five", 5); System.out.println("Using getOrDefault(): " + value2); ) )
Resultado
TreeMap: (One = 1, Three = 3, Two = 2) Usando get (): 3 Usando getOrDefault (): 5
Aqui, o getOrDefault()método não encontra a chave Cinco. Portanto, ele retorna o valor padrão 5 especificado.
Remover elementos TeeMap
remove(key)- retorna e remove a entrada associada à chave especificada de um TreeMapremove(key, value)- remove a entrada do mapa apenas se a chave especificada está associada ao valor especificado e retorna um valor booleano
Por exemplo,
import java.util.TreeMap; class Main ( public static void main(String() args) ( TreeMap numbers = new TreeMap(); numbers.put("One", 1); numbers.put("Two", 2); numbers.put("Three", 3); System.out.println("TreeMap: " + numbers); // remove method with single parameter int value = numbers.remove("Two"); System.out.println("Removed value: " + value); // remove method with two parameters boolean result = numbers.remove("Three", 3); System.out.println("Is the entry (Three=3) removed? " + result); System.out.println("Updated TreeMap: " + numbers); ) )
Resultado
TreeMap: (Um = 1, Três = 3, Dois = 2) Valor removido = 2 A entrada (Três = 3) foi removida? Mapa de árvore atualizado verdadeiro: (um = 1)
Substituir Elementos TreeMap
replace(key, value)- substitui o valor mapeado pela chave especificada pelo novo valorreplace(key, old, new)- substitui o valor antigo pelo novo valor apenas se o valor antigo já estiver associado à chave especificadareplaceAll(function)- substitui cada valor do mapa pelo resultado da função especificada
Por exemplo,
import java.util.TreeMap; class Main ( public static void main(String() args) ( TreeMap numbers = new TreeMap(); numbers.put("First", 1); numbers.put("Second", 2); numbers.put("Third", 3); System.out.println("Original TreeMap: " + numbers); // Using replace() numbers.replace("Second", 22); numbers.replace("Third", 3, 33); System.out.println("TreeMap using replace: " + numbers); // Using replaceAll() numbers.replaceAll((key, oldValue) -> oldValue + 2); System.out.println("TreeMap using replaceAll: " + numbers); ) )
Resultado
Original TreeMap: (First=1, Second=2, Third=3) TreeMap using replace(): (First=1, Second=22, Third=33) TreeMap using replaceAll(): (First=3, Second=24, Third=35)
In the above program notice the statement
numbers.replaceAll((key, oldValue) -> oldValue + 2);
Here, we have passed a lambda expression as an argument.
The replaceAll() method accesses all the entries of the map. It then replaces all the elements with the new values (returned from the lambda expression).
Methods for Navigation
Since the TreeMap class implements NavigableMap, it provides various methods to navigate over the elements of the treemap.
1. First and Last Methods
firstKey()- returns the first key of the mapfirstEntry()- returns the key/value mapping of the first key of the maplastKey()- returns the last key of the maplastEntry()- returns the key/value mapping of the last key of the map
For example,
import java.util.TreeMap; class Main ( public static void main(String() args) ( TreeMap numbers = new TreeMap(); numbers.put("First", 1); numbers.put("Second", 2); numbers.put("Third", 3); System.out.println("TreeMap: " + numbers); // Using the firstKey() method String firstKey = numbers.firstKey(); System.out.println("First Key: " + firstKey); // Using the lastKey() method String lastKey = numbers.lastKey(); System.out.println("Last Key: " + lastKey); // Using firstEntry() method System.out.println("First Entry: " + numbers.firstEntry()); // Using the lastEntry() method System.out.println("Last Entry: " + numbers.lastEntry()); ) )
Output
TreeMap: (First=1, Second=2, Third=3) First Key: First Last Key: Third First Entry: First=1 Last Entry: Third=3
2. Ceiling, Floor, Higher and Lower Methods
- higherKey() - Returns the lowest key among those keys that are greater than the specified key.
- higherEntry() - Returns an entry associated with a key that is lowest among all those keys greater than the specified key.
- lowerKey() - Returns the greatest key among all those keys that are less than the specified key.
- lowerEntry() - Returns an entry associated with a key that is greatest among all those keys that are less than the specified key.
- ceilingKey() - Returns the lowest key among those keys that are greater than the specified key. If the key passed as an argument is present in the map, it returns that key.
- ceilingEntry() - Returns an entry associated with a key that is lowest among those keys that are greater than the specified key. It an entry associated with the key passed an argument is present in the map, it returns the entry associated with that key.
- floorKey() - Returns the greatest key among those keys that are less than the specified key. If the key passed as an argument is present, it returns that key.
- floorEntry() - Returns an entry associated with a key that is greatest among those keys that are less than the specified key. If the key passed as argument is present, it returns that key.
For example,
import java.util.TreeMap; class Main ( public static void main(String() args) ( TreeMap numbers = new TreeMap(); numbers.put("First", 1); numbers.put("Second", 5); numbers.put("Third", 4); numbers.put("Fourth", 6); System.out.println("TreeMap: " + numbers); // Using higher() System.out.println("Using higherKey(): " + numbers.higherKey("Fourth")); System.out.println("Using higherEntry(): " + numbers.higherEntry("Fourth")); // Using lower() System.out.println("Using lowerKey(): " + numbers.lowerKey("Fourth")); System.out.println("Using lowerEntry(): " + numbers.lowerEntry("Fourth")); // Using ceiling() System.out.println("Using ceilingKey(): " + numbers.ceilingKey("Fourth")); System.out.println("Using ceilingEntry(): " + numbers.ceilingEntry("Fourth")); // Using floor() System.out.println("Using floorKey(): " + numbers.floorKey("Fourth")); System.out.println("Using floorEntry(): " + numbers.floorEntry("Fourth")); ) )
Output
TreeMap: (First=1, Fourth=6, Second=5, Third=4) Using higherKey(): Second Using higherEntry(): Second=5 Using lowerKey(): First Using lowerEntry(): First=1 Using ceilingKey(): Fourth Using ceilingEntry(): Fourth=6 Using floorkey(): Fourth Using floorEntry(): Fourth=6
3. pollFirstEntry() and pollLastEntry() Methods
pollFirstEntry()- returns and removes the entry associated with the first key of the mappollLastEntry()- returns and removes the entry associated with the last key of the map
For example,
import java.util.TreeMap; class Main ( public static void main(String() args) ( TreeMap numbers = new TreeMap(); numbers.put("First", 1); numbers.put("Second", 2); numbers.put("Third", 3); System.out.println("TreeMap: " + numbers); //Using the pollFirstEntry() method System.out.println("Using pollFirstEntry(): " + numbers.pollFirstEntry()); // Using the pollLastEntry() method System.out.println("Using pollLastEntry(): " + numbers.pollLastEntry()); System.out.println("Updated TreeMap: " + numbers); ) )
Output
TreeMap: (First=1, Second=2, Third=3) Using pollFirstEntry(): First=1 Using pollLastEntry(): Third=3 Updated TreeMap: (Second=2)
4. headMap(), tailMap() and subMap() Methods
headMap(key, booleanValue)
The headMap() method returns all the key/value pairs of a treemap before the specified key (which is passed as an argument).
The booleanValue parameter is optional. Its default value is false.
If true is passed as a booleanValue, the method also includes the key/value pair of the key which is passed as an argument.
For example,
import java.util.TreeMap; class Main ( public static void main(String() args) ( TreeMap numbers = new TreeMap(); numbers.put("First", 1); numbers.put("Second", 2); numbers.put("Third", 3); numbers.put("Fourth", 4); System.out.println("TreeMap: " + numbers); System.out.println("Using headMap() Method:"); // Using headMap() with default booleanValue System.out.println("Without boolean value: " + numbers.headMap("Fourth")); // Using headMap() with specified booleanValue System.out.println("With boolean value: " + numbers.headMap("Fourth", true)); ) )
Output
TreeMap: (First=1, Fourth=4, Second=2, Third=3) Using headMap() Method: Without boolean value: (First=1) With boolean value: (First=1, Fourth=4)
tailMap(key, booleanValue)
The tailMap() method returns all the key/value pairs of a treemap starting from the specified key (which is passed as an argument).
The booleanValue is an optional parameter. Its default value is true.
If false is passed as a booleanValue, the method doesn't include the key/value pair of the specified key.
For example,
import java.util.TreeMap; class Main ( public static void main(String() args) ( TreeMap numbers = new TreeMap(); numbers.put("First", 1); numbers.put("Second", 2); numbers.put("Third", 3); numbers.put("Fourth", 4); System.out.println("TreeMap: " + numbers); System.out.println("Using tailMap() Method:"); // Using tailMap() with default booleanValue System.out.println("Without boolean value: " + numbers.tailMap("Second")); // Using tailMap() with specified booleanValue System.out.println("With boolean value: " + numbers.tailMap("Second", false)); ) )
Output
TreeMap: (First=1, Fourth=4, Second=2, Third=3) Using tailMap() Method: Without boolean value: (Second=2, Third=3) With boolean value: (Third=3)
subMap(k1, bV1, k2, bV2)
The subMap() method returns all the entries associated with keys between k1 and k2 including the entry of k1.
The bV1 and bV2 are optional boolean parameters. The default value of bV1 is true and the default value of bV2 is false.
If false is passed as bV1, the method returns all the entries associated with keys between k1 and k2 without including the entry of k1.
If true is passed as bV2, the method returns all the entries associated with keys between k1 and k2 including the entry of k2.
For example,
import java.util.TreeMap; class Main ( public static void main(String() args) ( TreeMap numbers = new TreeMap(); numbers.put("First", 1); numbers.put("Second", 2); numbers.put("Third", 3); numbers.put("Fourth", 4); System.out.println("TreeMap: " + numbers); System.out.println("Using subMap() Method:"); // Using subMap() with default booleanValue System.out.println("Without boolean value: " + numbers.subMap("Fourth", "Third")); // Using subMap() with specified booleanValue System.out.println("With boolean value: " + numbers.subMap("Fourth", false, "Third", true)); ) )
Output
TreeMap: (First=1, Fourth=2, Second=2, Third=3) Using subMap() Method: Without boolean value: (Fourth=4, Second=2) With boolean value: (Second=2, Third=3)
Other Methods of TreeMap
| Method | Description |
|---|---|
clone() | Creates a copy of the TreeMap |
containsKey() | Searches the TreeMap for the specified key and returns a boolean result |
containsValue() | Searches the TreeMap for the specified value and returns a boolean result |
size() | Returns the size of the TreeMap |
clear() | Removes all the entries from the TreeMap |
TreeMap Comparator
In all the examples above, treemap elements are sorted naturally (in ascending order). However, we can also customize the ordering of keys.
For this, we need to create our own comparator class based on which keys in a treemap are sorted. For example,
import java.util.TreeMap; import java.util.Comparator; class Main ( public static void main(String() args) ( // Creating a treemap with a customized comparator TreeMap numbers = new TreeMap(new CustomComparator()); numbers.put("First", 1); numbers.put("Second", 2); numbers.put("Third", 3); numbers.put("Fourth", 4); System.out.println("TreeMap: " + numbers); ) // Creating a comparator class public static class CustomComparator implements Comparator ( @Override public int compare(String number1, String number2) ( int value = number1.compareTo(number2); // elements are sorted in reverse order if (value> 0) ( return -1; ) else if (value < 0) ( return 1; ) else ( return 0; ) ) ) )
Output
TreeMap: (Third=3, Second=2, Fourth=4, First=1)
No exemplo acima, criamos um mapa de árvore passando a classe CustomComparator como um argumento.
A classe CustomComparator implementa a Comparatorinterface.
Em seguida, substituímos o compare()método para classificar os elementos na ordem inversa.
Para saber mais, visite Java Comparator (documentação oficial do Java).
