Interview Questions and Answers for 'Hc' | Search Interview Question

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Q181. What is the use of defining equals , compareTo and hashcode methods in a class ? Where are they used ?

Ans. equals, compareTo and hashcode are of use when the objects are used within collections.

Equals helps with collections that helps maintaining only unique objects ( like Set )

compare and compareTo helps with collections that helps maintaining objects in order ( TreeSet, TreeMap etc )

hascode helps with collections that facilitates hash searching ( like hashSet, hashMap etc )

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Q182. Write a program to make an array act as a set.

Core Java

Ans. public Set convertArrayToList(T array[]) {
Set set = new HashSet<>(Arrays.asList(array));
return set;
}

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Q183. Write a unit test case using java 8.

JUnit

Ans. public List convertAllToUpperCase(List words) {
return words.stream().map(String::toUpperCase).collect(Collectors.toList());
}

@Test
public void testAllToUpperCase() {
List expected = Arrays.asList("JAVA8", "STREAMS");
List result = convertAllToUpperCase(Arrays.asList("java8", "streams"));
assertEquals(expected, result);
}

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Q184. How would you design the database schema for an event?

Database

Ans. Broad question, but if the company need velocity, think about use a NO SQL instead of regular SQL databases.

Also prefers materialized views instead of joins to fetch data quickly.

Regarding the database design, there are very good design tools for professional database (to develop proper indexes and good database design) one of the best is QuickDBD

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Q185. Which of the following is false ?

Core Java

a. A Class cannot override both hashcode and equals method.

b. A class can override both hashcode and equals method.

c. A Class must override hashCode method if its overridding equal method.

d. A Class can override hashCode even if its not overridding equals method.

Ans.a. A Class cannot override both hashcode and equals method.

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