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What is the contract of hashCode() and equals() methods in Java?

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Pragya Keshap answered on February 4, 2023 Popularity 5/10 Helpfulness 2/10

answer What is the contract of hashCode() and equals() methods in Java?

related equals() and hashcode() methods in java

What is the contract of hashCode() and equals() methods in Java?

Comment

Contract of hashCode() and equals() methods is as follows in Java:

If object1.equals(object2), then object1.hashCode() ==

object2.hashCode() should always be true. It means if two objects

are equal then their hashCode should be same.

If object1.hashCode() == object2.hashCode() is true, it does not

guarantee that object1.equals(object2). It means if two objects have

same hashCode, then can still have different values so that may not

be equal objects

public class MainClass {
   public static void main(String[] args) {
      MainClass mainClass = new MainClass();
      TestClass obj1 = new TestClass(1);
      TestClass obj2 = new TestClass(1);
      mainClass.test1(obj1, obj2);
      TestClass obj3 = new TestClass(1);
      TestClass obj4 = new TestClass(2);
      mainClass.test2(obj3, obj4);
   }
   public void test1(TestClass obj1, TestClass obj2) {
      if (obj1.equals(obj2)) {
         System.out.println("Object One and Object Two are equal");
      }
      else {
         System.out.println("Object One and Object Two are not equal");
      }
   }
   public void test2(TestClass obj3, TestClass obj4) {
      if (obj3.equals(obj4)) {
         System.out.println("Object Three and Object Four are equal");
      }
      else {
         System.out.println("Object Three and Object Four are not equal");
      }
   }
}
class TestClass {
   private int val;
   TestClass(int val) {
      this.val = val;
   }
   public int getValue() {
      return val;
   }
   @Override
   public boolean equals(Object o) {
      // null check
      if (o == null) {
         return false;
      }
      // this instance check
      if (this == o) {
         return true;
      }
      // instanceof Check and actual value check
      if ((o instanceof TestClass) && (((TestClass) o).getValue() == this.val)) {
         return true;
      }
       else {
         return false;
      }
   }
   @Override
   public int hashCode() {
      int result = 0;
      result = (int) (val / 11);
      return result;
   }
}

https://www.tutorialspoint.com/what-is-the-contract-between-equals-and-hashcode-methods-in-java#:~:text=General%20contract%20associated%20with%20hashCode()%20method&text=If%20two%20objects%20are%20equal,value%20for%20both%20the%20objects.

Popularity 5/10 Helpfulness 2/10 Language java

Source: Grepper

Tags: contract java methods

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Contributed on Feb 04 2023

Pragya Keshap

0 Answers Avg Quality 2/10

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equals() and hashcode() methods in java

Comment

a & b are equal variables, and their respective hash values are: 1965574029 & 1965574029

c & d are Un-equal variables, and their respective hash values are: 74113750 & 71933245

Popularity 5/10 Helpfulness 1/10 Language java

Source: www.javatpoint.com

Tags: java methods

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Contributed on Feb 28 2024

Aswin Sundar

0 Answers Avg Quality 2/10

What is the contract of hashCode() and equals() methods in Java?

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