How we implement hashCode and equals method in Java?

How we implement hashCode and equals method in Java?

The implementation of equals() and hashCode() should follow these rules.

  1. If o1. equals(o2) , then o1. hashCode() == o2. hashCode() should always be true .
  2. If o1. hashCode() == o2. hashCode is true, it doesn’t mean that o1. equals(o2) will be true .

Why do we implement hashCode and equals?

You must override hashCode() in every class that overrides equals(). Failure to do so will result in a violation of the general contract for Object. hashCode(), which will prevent your class from functioning properly in conjunction with all hash-based collections, including HashMap, HashSet, and Hashtable.

What is the default implementation of hashCode and equals?

Uses of hashCode() and equals() Methods Its default implementation simply checks the object references of two objects to verify their equality. By default, two objects are equal if and only if they are refer to the same memory location.

What is the default implementation of hashCode in Java?

In Java, hashCode() by default is a native method, which means that the method has a modifier ‘native’, when it is implemented directly in the native code in the JVM. Used to digest all the data stored in an instance of the class into a single hash value i.e., a 32-bit signed integer.

What is the contract between equals and hashCode in Java?

The Contract Between equals() and hashcode() If two objects are equal according to the equals(Object) method, then calling the hashcode() method on each of the two objects must produce the same integer result.

What is hashCode implementation?

“As much as is reasonably practical, the hashCode() method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)”

How do you implement equals in Java?


  1. Make sure to override equals(Object) so our method is always called.
  2. Include a self and null check for an early return in simple edge cases.
  3. Use getClass to allow subtypes their own implementation (but no comparison across subtypes) or use instanceof and make equals final (and subtypes can equal).

How do you create an equals method in Java?

Java String equals() Method Example 2

  1. public class EqualsExample2 {
  2. public static void main(String[] args) {
  3. String s1 = “javatpoint”;
  4. String s2 = “javatpoint”;
  5. String s3 = “Javatpoint”;
  6. System.out.println(s1.equals(s2)); // True because content is same.
  7. if (s1.equals(s3)) {
  8. System.out.println(“both strings are equal”);

What is the need for overriding equals () method in Java?

Why we override equals() method? It needs to be overridden if we want to check the objects based on the property. For example, we want to check the equality of employee object by the id. Then, we need to override the equals() method.

What is an equals method in Java?

Java String equals() Method The equals() method compares two strings, and returns true if the strings are equal, and false if not.

What is == and equals 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. If a class does not override the equals method, then by default, it uses the equals(Object o) method of the closest parent class that has overridden this method.