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hash table implementation with equals and hashcode example


Hashtable:

Hashtable extends Dictionary class and implements Map interface. It contains elements in key-value pair. It not allowed duplicate key. It is synchronized. It can’t contain null key or value. It uses hashcode() method for finding the position of the elements.

Example:

package com.codesjava;
 
import java.util.Hashtable;
 
class Employee{    
    private String name;
    private int salary;
    private int id;
 
    public Employee(int id, String name, int salary){
    	this.id = id;
        this.name = name;
        this.salary = salary;
    }
 
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getSalary() {
        return salary;
    }
    public void setSalary(int salary) {
        this.salary = salary;
    }
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String toString(){
        return "Id: "+this.id+", Name: "+this.name+", Salary: "+this.salary;
    }
 
	@Override
	public int hashCode() {
	    System.out.println("In hashcode");
	    return this.getId();
	}
 
	@Override
	public boolean equals(Object obj) {
		Employee e = null;
	    if(obj instanceof Employee){
	        e = (Employee) obj;
	    }
	    System.out.println("In equals");
	    if(this.getId() == e.getId()){
	        return true;
	    } else {
	        return false;
	    }  
	}
}
 
public class Test {
  public static void main(String args[]){
	Hashtable<Employee,String> hashtable = new Hashtable<Employee, String>();
	hashtable.put(new Employee(1,"Jai",50000), "JAI");
	hashtable.put(new Employee(2,"Mahesh",80000), "MAHESH");
	hashtable.put(new Employee(3,"Vishal",60000), "VISHAL");
	hashtable.put(new Employee(4,"Hemant",64000), "HEMANT");
	System.out.println("Fecthing value by creating new key:");
        Employee e = new Employee(3,"Vikas",54000);
        System.out.println("Newly created element: " + e);
        System.out.println("Element with new key - "+hashtable.get(e));
  }
}

Output

In hashcode
In hashcode
In hashcode
In hashcode
Fecthing value by creating new key:
Newly created element: Id: 3, Name: Vikas, Salary: 54000
In hashcode
In equals
Element with new key - VISHAL
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