Para implementar una tabla hash, debemos usar la clase de tabla hash, que asignará claves a los valores. La clave o los valores de la tabla hash deben ser un objeto no nulo. Para almacenar y recuperar datos de la tabla hash, los objetos no nulos que se usan como claves deben implementar el método hashCode() y el método equals() . Hashtable produce resultados en forma desordenada y desordenada.
Ejemplo 1:
En el siguiente ejemplo, usamos Integer como claves y Student object como valores. Para evitar claves duplicadas, ha implementado los métodos hashCode() y equals(). En caso de que ingresemos una clave duplicada, la tabla hash elimina las claves duplicadas automáticamente.
Java
// Java Programs to implement hashtable with
// equals() and hashcode() method
// Importing hashtable and Scanner classes
// from java.util package
import java.util.Hashtable;
import java.util.Scanner;
// Class 1
// Helper class
class Student {
// Initializing the instance variables
// of this class
private int sid;
private String name;
private String mobno;
// Constructor of student class
// to initialize the variable values
public Student(int sid, String name, String mobno)
{
// Super keyword refers to parent object
super();
// This keyword refers to current object
// in a constructor
this.sid = sid;
this.name = name;
this.mobno = mobno;
}
// Method 1
// getter for Sid
public int getSid() { return sid; }
// Method 2
// setter for Sid
public void setSid(int sid) { this.sid = sid; }
// Method 3
// getter for name
public String getName() { return name; }
// Method 4
// setter for name
public void setName(String name) { this.name = name; }
// Method 5
// getter for mobno
public String getMobno() { return mobno; }
// Method 6
// setter for mobno
public void setMobno(String mobno)
{
this.mobno = mobno;
}
// Now, overriding methods
// Overriding of hashCode
// @Override
public int hashCode() { return this.getSid(); }
// Overriding of equals
// @Override
public boolean equals(Object o)
{
if (o instanceof Student) {
return (this.sid) == (((Student)o).sid);
}
return false;
}
// Overriding of toString() method
// @Override
public String toString()
{
return "id=" + sid + ", name=" + name
+ ", mobno=" + mobno;
}
}
// Class 2
// Main class for hashtableExample
public class GFG {
// Main driver method
public static void main(String a[])
{
// Initializing the hashtable with
// key as integer and value as Student object
// Creating an Hashtable object
// Declaring object of Integer and String type
Hashtable<Integer, Student> list
= new Hashtable<Integer, Student>();
// Adding elements to the hashtable
// Custom inputs
list.put(101,
new Student(101, "Ram", "9876543201"));
list.put(102,
new Student(102, "Shyam", "8907685432"));
list.put(103,
new Student(103, "Mohan", "8907896785"));
list.put(104, new Student(104, "Lakshman",
"8909006524"));
list.put(105,
new Student(105, "Raman", "6789054321"));
// Display message
System.out.println("Traversing the hash table");
// Traversing hashtable using for-each loop
for (Student i : list.values()) {
System.out.println(i);
}
// New line
System.out.println();
// Display message
System.out.println(
"Search the student by student id");
// New line
System.out.println();
// Display message
System.out.println("Enter the student id : ");
// Custom value in a variable is assigned
int temp = 104;
// Display message
System.out.println("104");
// Traversing hashtable using for-each loop
for (Student s : list.values()) {
if (s.getSid() == temp) {
// If student found, simply print the
// student details
System.out.println("Student is : " + s);
// Exit the program
System.exit(0);
}
}
// If student not found execute the command
// Print the display message
System.out.println("Student not found..");
}
}
Producción
Traversing the hash table id=105, name=Raman, mobno=6789054321 id=104, name=Lakshman, mobno=8909006524 id=103, name=Mohan, mobno=8907896785 id=102, name=Shyam, mobno=8907685432 id=101, name=Ram, mobno=9876543201 Search the student by student id Enter the student id : 104 Student is : id=104, name=Lakshman, mobno=8909006524
Ejemplo 2
Aquí, en esta tabla hash, la string como claves y el objeto Student como valores. Para evitar claves duplicadas, ha implementado los métodos hashCode() y equals() . En caso de que ingresemos la clave duplicada, la tabla hash elimina las claves duplicadas automáticamente
Java
// Main class
import java.util.Hashtable;
import java.util.Scanner;
public class HashtableExample2 {
public static void main(String a[])
{
// Initializing the hashtable with
// key as String and values as Student object
Hashtable<String, Student> list
= new Hashtable<String, Student>();
list.put("Ram",
new Student(1, "Ram", "8907654321"));
list.put("Sita",
new Student(2, "Sita", "9809876543"));
list.put("Mohan",
new Student(3, "Mohan", "9098765421"));
list.put("Soham",
new Student(4, "Soham", "7898790678"));
list.put("Lakhan",
new Student(5, "Lakhan", "7890567845"));
// Traversing the hashtable using for-each loop
System.out.println("Traversing the hash table");
for (Student i : list.values()) {
System.out.println(i);
}
System.out.println();
// Search the student using their names
System.out.println(
"Search the student by student id");
System.out.println();
System.out.println("Enter the student id : ");
int temp = 3;
System.out.println("3");
for (Student s : list.values()) {
if (s.getRollno() == temp) {
// If found, then print the student details
System.out.println("Student is : " + s);
// Terminate the program
System.exit(0);
}
}
// If student not found, print that there is no
// student
System.out.println("Student not found..");
}
}
// Student class
class Student {
// Initializing the instance variables
private int rollno;
private String name;
private String mobno;
// Constructor to initialize the values of variables
public Student(int rollno, String name, String mobno)
{
super();
this.rollno = rollno;
this.name = name;
this.mobno = mobno;
}
// getter for roll no
public int getRollno() { return rollno; }
// setter for roll no
public void setRollno(int rollno)
{
this.rollno = rollno;
}
// getter for name
public String getName() { return name; }
// setter for name
public void setName(String name) { this.name = name; }
// getter for mobno
public String getMobno() { return mobno; }
// setter for mobno
public void setMobno(String mobno)
{
this.mobno = mobno;
}
// Overriding of hashCode
@Override public int hashCode()
{
return this.getRollno();
}
// Overriding of equals
// @Override
public boolean equals(Object o)
{
if (o instanceof Student) {
return (this.rollno) == (((Student)o).rollno);
}
return false;
}
// Overriding of toString
@Override public String toString()
{
return "Rollno=" + rollno + ", name=" + name
+ ", mobno=" + mobno;
}
}
Producción
Traversing the hash table Rollno=2, name=Sita, mobno=9809876543 Rollno=3, name=Mohan, mobno=9098765421 Rollno=5, name=Lakhan, mobno=7890567845 Rollno=4, name=Soham, mobno=7898790678 Rollno=1, name=Ram, mobno=8907654321 Search the student by student id Enter the student id : 3 Student is : Rollno=3, name=Mohan, mobno=9098765421
Publicación traducida automáticamente
Artículo escrito por snigdha_yambadwar y traducido por Barcelona Geeks. The original can be accessed here. Licence: CCBY-SA