Core Java - Interview Questions and Answers for 'Hash code' | Search Interview Question

Core Java - Interview Questions and Answers for 'Hash code' - 6 question(s) found - Order By Rating

Q1. How are hash codes generated ?

Data Structure

Ans. Use hashCode() which returns an integer value, generated by a hashing algorithm

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Q2. Why String is popular HashMap key in Java?

Core Java

Ans. Since String is immutable, its hashcode is cached at the time of creation and it doesnt need to be calculated again. This makes it a great candidate for key in a Map and its processing is fast than other HashMap key objects. This is why String is mostly used Object as HashMap keys.

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Q3. public class a {
   public static void main(String args[]){
      final String s1=""job"";
      final String s2=""seeker"";
      String s3=s1.concat(s2);
      String s4=""jobseeker"";
      System.out.println(s3==s4); // Output 1
      System.out.println(s3.hashCode()==s4.hashCode()); Output 2
   }
}

What will be the Output 1 and Output 2 ?

Core Java

Ans. S3 and S4 are pointing to different memory location and hence Output 1 will be false.

Hash code is generated to be used as hash key in some of the collections in Java and is calculated using string characters and its length. As they both are same string literals, and hence their hashcode is same.Output 2 will be true.

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Q4. What is the use of HashCode in objects ?

Core Java

Ans. Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc.

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Very Frequently asked. Favorite question in walkins and telephonic interviews. Usually among first few questions. Asked in different variants. Must know for intermediate and expert professionals.Among Top 10 frequently asked questions.

Q5. What is rule regarding overriding equals and hashCode method ?

Core Java

Ans. A Class must override the hashCode method if its overriding the equals method.

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Q6. What is collision in hash collections ?

Core Java

Ans. Collision is the situation when two different elements have the same Hash Code.

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