Los objetos duplicados definidos por el usuario como una clave de Java LinkedHashMap se pueden eliminar y lograr mediante la implementación de métodos equals y hashcode en los objetos definidos por el usuario.
Ejemplo:
Input : LinkedHashMap = [{[Apple, 40], Kashmir}, {[Grapes, 80], Nashik}]
Duplicate key = {[Grapes, 80], Delhi}
Output: LinkedHashMap = [{[Apple, 40], Kashmir}, {[Grapes, 80], Delhi}]
Sintaxis:
igual() Método:
public boolean equals (Object obj) // This method checks if some other Object // passed to it as an argument is equal to // the Object on which it is invoked.
Método hashCode():
public int hashCode() // This method returns the hash code value // for the object on which this method is invoked.
A continuación se muestra la implementación del enunciado del problema:
Java
// Java Program to eliminate duplicate user defined
// objects as a key from Java LinkedHashMap
import java.util.*;
class Employee {
private String name;
private int id;
// Constructor
public Employee(String name, int id)
{
this.name = name;
this.id = id;
}
// HashCode Method
public int hashCode()
{
System.out.println("In hashcode method");
int hashcode = 0;
return hashcode;
}
// Equals Method
public boolean equals(Object obj)
{
System.out.println("In equals method");
if (obj instanceof Employee) {
Employee emp = (Employee)obj;
return (emp.name.equals(this.name)
&& emp.id == this.id);
}
else {
return false;
}
}
// Getters and Setters
public String getName() { return name; }
public void setName(String name) { this.name = name; }
public int getId() { return id; }
public void setId(int id) { this.id = id; }
public String toString()
{
return "Employee Id: " + id + " Name: " + name;
}
}
// Driver code
public class Duplicate_Value {
public static void main(String a[])
{
// LinkedHashMap initialization
LinkedHashMap<Employee, Integer> lhm
= new LinkedHashMap<Employee, Integer>();
// Adding entries in LinkedHashMap
lhm.put(new Employee("John", 1020), 1);
lhm.put(new Employee("Ravi", 1040), 2);
lhm.put(new Employee("Jaya", 1030), 3);
// Print LinkedHashMap
for (Map.Entry<Employee, Integer> entry :
lhm.entrySet()) {
System.out.println(entry.getKey() + "=>"
+ entry.getValue());
}
// Create duplicate entry
Employee duplicate = new Employee("John", 1020);
System.out.println("Inserting duplicate record...");
// Add duplicate entry
lhm.put(duplicate, 4);
System.out.println("After insertion:");
for (Map.Entry<Employee, Integer> entry :
lhm.entrySet()) {
System.out.println(entry.getKey() + "=>"
+ entry.getValue());
}
}
}
Producción
In hashcode method In hashcode method In equals method In hashcode method In equals method Employee Id: 1020 Name: John Inserting duplicate record... In hashcode method In equals method After insertion: Employee Id: 1020 Name: John
Complejidad de tiempo: O(1)