A. eliminar (tecla de objeto)
El método remove (clave de objeto) de la clase ConcurrentHashmap en Java se usa para eliminar la asignación del mapa. Si la clave no existe en el mapa, entonces esta función no hace nada.
Sintaxis:
public V remove(Object key)
Parámetros:
This method accepts a mandatory parameter key which is the key that needs to be removed
Valor devuelto:
This method returns the previous value associated with key, or null if there was no mapping for key.
Excepciones:
This method throws NullPointerException if the specified key is null.
A continuación se muestran los programas para ilustrar el método remove():
Programa 1:
Java
// Java program to demonstrate remove() method
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
public class ConcurrentHashMapExample {
public static void main(String[] args)
{
// Creating ConcurrentHashMap
Map<String, String> my_cmmap
= new ConcurrentHashMap<String, String>();
// Adding elements to the map
// using put() method
my_cmmap.put("1", "1");
my_cmmap.put("2", "1");
my_cmmap.put("3", "1");
my_cmmap.put("4", "1");
my_cmmap.put("5", "1");
my_cmmap.put("6", "1");
// Printing the map
System.out.println("Map: " + my_cmmap);
System.out.println();
// Removing the mapping
// with existing key 6
// using remove() method
String valueRemoved = my_cmmap.remove("6");
// Printing the map after remove()
System.out.println(
"After removing mapping with key 6:");
System.out.println("Map: " + my_cmmap);
System.out.println("Value removed: "
+ valueRemoved);
System.out.println();
// Removing the mapping
// with non-existing key 10
// using remove() method
valueRemoved = my_cmmap.remove("10");
// Printing the map after remove()
System.out.println(
"After removing mapping with key 10:");
System.out.println("Map: " + my_cmmap);
System.out.println("Value removed: "
+ valueRemoved);
}
}
Producción
Map: {1=1, 2=1, 3=1, 4=1, 5=1, 6=1}
After removing mapping with key 6:
Map: {1=1, 2=1, 3=1, 4=1, 5=1}
Value removed: 1
After removing mapping with key 10:
Map: {1=1, 2=1, 3=1, 4=1, 5=1}
Value removed: null
Programa 2: Para demostrar NullPointerException con clave nula
Java
// Java program to demonstrate remove() method
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
public class ConcurrentHashMapExample {
public static void main(String[] args)
{
// Creating ConcurrentHashMap
Map<String, String> my_cmmap
= new ConcurrentHashMap<String, String>();
// Adding elements to the map
// using put() method
my_cmmap.put("1", "1");
my_cmmap.put("2", "1");
my_cmmap.put("3", "1");
my_cmmap.put("4", "1");
my_cmmap.put("5", "1");
my_cmmap.put("6", "1");
// Printing the map
System.out.println("Map: " + my_cmmap);
System.out.println();
try {
// Removing the mapping with null key
// using remove() method
my_cmmap.remove(null);
}
catch (Exception e) {
System.out.println("Exception: " + e);
}
}
}
Producción
Map: {1=1, 2=1, 3=1, 4=1, 5=1, 6=1}
Exception: java.lang.NullPointerException
B. eliminar (clave de objeto, valor de objeto)
El método remove (clave de objeto, valor de objeto) de la clase ConcurrentHashmap en Java se usa para eliminar la asignación del mapa. La asignación con el par especificado (clave, valor) se busca en el mapa y se elimina si se encuentra, y devuelve verdadero. Si la clave no existe en el mapa, entonces esta función no hace nada y devuelve falso.
Sintaxis:
public boolean remove(Object key, Object value)
Parámetros:
This method accepts two parameters key - key with which the specified value is associated. value - value expected to be associated with the specified key.
Valor devuelto:
This method returns true if the value was removed. Else it returns false.
Excepciones:
This method throws NullPointerException if the specified key is null.
A continuación se muestran los programas para ilustrar el método remove():
Programa 1:
Java
// Java program to demonstrate remove() method
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
public class ConcurrentHashMapExample {
public static void main(String[] args)
{
// Creating ConcurrentHashMap
Map<String, String> my_cmmap
= new ConcurrentHashMap<String, String>();
// Adding elements to the map
// using put() method
my_cmmap.put("1", "1");
my_cmmap.put("2", "1");
my_cmmap.put("3", "1");
my_cmmap.put("4", "1");
my_cmmap.put("5", "1");
my_cmmap.put("6", "1");
// Printing the map
System.out.println("Map: " + my_cmmap);
System.out.println();
// Removing the mapping
// with existing pair 6, 1
// using remove() method
boolean valueRemoved = my_cmmap.remove("6", "1");
// Printing the map after remove()
System.out.println(
"After removing mapping with pair (6, 1):");
System.out.println("Map: " + my_cmmap);
System.out.println("Was value removed: "
+ valueRemoved);
System.out.println();
// Removing the mapping
// with non-existing pair 1, 2
// using remove() method
valueRemoved = my_cmmap.remove("1", "2");
// Printing the map after remove()
System.out.println(
"After removing mapping with pair (1, 2):");
System.out.println("Map: " + my_cmmap);
System.out.println("Was value removed: "
+ valueRemoved);
}
}
Producción
Map: {1=1, 2=1, 3=1, 4=1, 5=1, 6=1}
After removing mapping with pair (6, 1):
Map: {1=1, 2=1, 3=1, 4=1, 5=1}
Was value removed: true
After removing mapping with pair (1, 2):
Map: {1=1, 2=1, 3=1, 4=1, 5=1}
Was value removed: false
Programa 2: Para demostrar NullPointerException con clave nula
Java
// Java program to demonstrate
// remove(key, value) null key
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
public class ConcurrentHashMapExample {
public static void main(String[] args)
{
// Creating ConcurrentHashMap
Map<String, String> my_cmmap
= new ConcurrentHashMap<String, String>();
// Adding elements to the map
// using put() method
my_cmmap.put("1", "1");
my_cmmap.put("2", "1");
my_cmmap.put("3", "1");
my_cmmap.put("4", "1");
my_cmmap.put("5", "1");
my_cmmap.put("6", "1");
// Printing the map
System.out.println("Map: " + my_cmmap);
System.out.println();
try {
// Removing the mapping
// with null key
// using remove() method
my_cmmap.remove(null, "1");
}
catch (Exception e) {
System.out.println("Exception: " + e);
}
}
}
Producción
Map: {1=1, 2=1, 3=1, 4=1, 5=1, 6=1}
Exception: java.lang.NullPointerException
Programa 3 : Para demostrar NullPointerException con el valor nulo
Java
// Java program to demonstrate
// remove(key, value) null value
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
public class ConcurrentHashMapExample {
public static void main(String[] args)
{
// Creating ConcurrentHashMap
Map<String, String> my_cmmap
= new ConcurrentHashMap<String, String>();
// Adding elements to the map
// using put() method
my_cmmap.put("1", "1");
my_cmmap.put("2", "1");
my_cmmap.put("3", "1");
my_cmmap.put("4", "1");
my_cmmap.put("5", "1");
my_cmmap.put("6", "1");
// Printing the map
System.out.println("Map: " + my_cmmap);
try {
// Removing the mapping with correct key and
// null value using remove() method
my_cmmap.remove("1", null);
my_cmmap.remove("7", null);
}
catch (Exception e) {
System.out.println("Exception: " + e);
}
}
}
Producción
Map: {1=1, 2=1, 3=1, 4=1, 5=1, 6=1}