Table of Contents
- 1 What is the relation between equals and hashCode?
- 2 What is the difference between hashCode and equals?
- 3 Why do we override hashCode and equals method?
- 4 Can two equal Object have the different hashCode?
- 5 How is hash code calculated?
- 6 What is the difference between the equals method and the == operator in Java?
- 7 Can two objects have the same hash code?
- 8 When does hashCode return the same integer?
What is the relation between equals and hashCode?
The contract between equals() and hashCode() is: 1) If two objects are equal, then they must have the same hash code. 2) If two objects have the same hash code, they may or may not be equal. The idea behind a Map is to be able to find an object faster than a linear search.
What is the difference between hashCode and equals?
hashCode is a method by which a class implicitly or explicitly break down the data stored in an instance of the class into a single hash value. The method equals is used to compare two objects. The method is used in hashing to decide which group an object should be placed into.
What is the hashCode () and equal () function?
Java hashCode() Java Object hashCode() is a native method and returns the integer hash code value of the object. If two objects are equal according to equals() method, then their hash code must be same. If two objects are unequal according to equals() method, their hash code are not required to be different.
What is difference between hashCode () and equals in Java?
hashCode() does not return the object’s reference, but a hash of the object, computed in some way. equals(obj2) is true then obj1. hasCode() must be true to be a valid implementation. Reason: hashCode just returns int value for an Object, even two different objects can have same hashCode integer.
Why do we override hashCode and equals method?
In order to use our own class objects as keys in collections like HashMap, Hashtable etc.. , we should override both methods ( hashCode() and equals() ) by having an awareness on internal working of collection. Otherwise, it leads to wrong results which we are not expected.
Can two equal Object have the different hashCode?
An object’s hashCode method must take the same fields into account as its equals method. So you will have equal objects with different hash codes. For example, calling contains() on a HashMap will return false, even though the object has been added.
When you are writing equals () method which other method or methods you need to override?
“If two objects are equal using Object class equals method, then the hashcode method should give the same value for these two objects.” So, if in our class we override equals() we should override hashcode() method also to follow this rule.
Can two equal objects have the different hash code?
But yes, you can have two different objects with the same hashcode. But that should not be the general case, a real implementation should give different hashcodes for different values most of the time.
How is hash code calculated?
Java String hashCode() method example
- String hashCode() method. The hash code for a String object is computed as: s[0]*31^(n-1) + s[1]*31^(n-2) + … + s[n-1] where :
- Java String hashCode() example. Java program for how to calculate hashcode of string. StringExample.java. public class StringExample.
What is the difference between the equals method and the == operator in Java?
In simple words, == checks if both objects point to the same memory location whereas . equals() evaluates to the comparison of values in the objects.
Can we override only hashCode without equals?
Only Override HashCode, Use the default Equals: Only the references to the same object will return true. In other words, those objects you expected to be equal will not be equal by calling the equals method.
What is the difference between equals() and hashCode() method?
If two Objects are equal, according to the equals (Object) method, then hashCode () method must produce the same Integer on each of the two Objects. If two Objects are unequal, according to the equals (Object) method, It is not necessary the Integer value produced by hashCode () method on each of the two Objects will be distinct.
Can two objects have the same hash code?
A contract is: If two objects are equal then they should have the same hashcode and if two objects are not equal then they may or may not have same hash code. Try using your object as key in HashMap (edited after comment from joachim-sauer), and you will start facing trouble.
When does hashCode return the same integer?
Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified.
What is hashCode in Java?
hashcode(): Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified.