What is difference between hash code and equals
Both hashCode and equals method is derived from Object class which is superclass of all and it belongs to java.lang package
Answer: Below are differences:
| HashCode | Equals |
| It return hash code value of the object | It returns true if other object is “equal to” this one otherwise returns false |
| Both have general contract between them which says that equal objects should have same hash code | It follows the same general contract which says that equal objects should have same hash code |
| For any non-null values if “a” and “b” are equals, it means they are same object then it will return same hash code value. | For any non-null values “a” and “b” this method return true if both a and b refer to the same object ( a == b is true then both have same reference) |
| Hash code method defined in class Object and it returns distinct integers value for distinct objects | Equals provide no information about it |
| Whenever hash code method invokes multiple time on the same object then it consistently returns same integer value | It compares object reference and don’t provide its integer value |
| Method details: public int hashCode() – It returns hashcode of the object | Method detail: public boolean equals(Object obj) – compare object and returns value |
| You cannot call hashcode method on null object it will throw nullpointerexception | You can compare using equals for reference with for example “a”, a.equals(null) should return false |
| If two objects are equals then it will return same hash code | But if two object has same hash code they may or may not be equal |
Please see example below:
package com.javahonk.setTest; public class HashCodeEqualsTest { public static void main(String[] args) { Employee e1 = new Employee("Java", "1000"); Employee e2 = new Employee("Honk", "1000"); Employee e3 = new Employee("Bob", "3000"); System.out.println("e1 and e2 are equal: " + e1.equals(e2)); System.out.println("e1 and e3 not equal: " + e1.equals(e3)); System.out.println(); System.out.println("e1 hash code: " + e1.hashCode()); System.out.println("e2 hash code: " + e2.hashCode()); System.out.println("e3 hash code: " + e3.hashCode()); } } class Employee { String name; String salary; public Employee(String name, String salary) { super(); this.name = name; this.salary = salary; } /* * (non-Javadoc) * * @see java.lang.Object#equals(java.lang.Object) */ @Override public boolean equals(Object obj) { boolean result = false; if (obj instanceof Employee) { Employee employee = (Employee) obj; if (this.salary == employee.salary) { result = true; } } return result; } /* (non-Javadoc) * @see java.lang.Object#hashCode() */ @Override public int hashCode() { int hashcodeValue = 10; hashcodeValue = this.name.hashCode(); hashcodeValue = this.salary.hashCode(); return hashcodeValue; } }
Output:
