Why do we need to override hashCode and equals method C#?

Why do we need to override hashCode and equals method C#?

It is because the framework requires that two objects that are the same must have the same hashcode. If you override the equals method to do a special comparison of two objects and the two objects are considered the same by the method, then the hash code of the two objects must also be the same.

Why GetHashCode is used in C#?

A hash code is a numeric value which is used to insert and identify an object in a hash-based collection. The GetHashCode method provides this hash code for algorithms that need quick checks of object equality.

What happens if we override equals and not hashCode?

Overriding only equals() method without overriding hashCode() causes the two equal instances to have unequal hash codes, which violates the hashCode contract (mentioned in Javadoc) that clearly says, if two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two …

When should we override GetHashCode?

If you’re implementing a reference type, you should consider overriding the Equals method if your type looks like a base type, such as Point, String, BigNumber, and so on. Override the GetHashCode method to allow a type to work correctly in a hash table.

Can you use == to compare strings in C#?

You can check the equality of strings using two ways: Using == operator. Using Equals() method….== vs Equals.

== Equals()
Compares the content of strings. Compares the content of strings.

Can constructor be overridden?

Constructor looks like method but it is not. It does not have a return type and its name is same as the class name. But, a constructor cannot be overridden. If you try to write a super class’s constructor in the sub class compiler treats it as a method and expects a return type and generates a compile time error.

Can hashCode return negative value?

Negative hashcode is perfectly valid! It is perfectly legal to have negative hash codes, and if you are looking for hash values as used in hash-based collections you can use Math. abs(hash) . This can also give you negative numbers when hash is bigger than 2^31, and the best way would be to use a shift mask (key.

Is string equals null safe C#?

Compare Case-Sensitive Strings What happens if a string is null? As you can see above, there is no problem with == operator if a string is null. But, calling the Equals() method on null will throw the NullReferenceException .

Which class is not thread safe?

When designing a class that may be used for concurrent programming—that is, a class whose instances may be used by more than one thread at a time—it is imperative that you make sure the class is ” thread-safe.” Consider the IntList class of Example 2-7. This class is not thread safe.

Why did I override equals with hashCode?

The same applies to hashcode – the default implmentation is typically based on a memory address of the reference. Because you did override Equals it means the correct behavior is to compare whatever you implemented on Equals and not the references, so you should do the same for the hashcode.

What is the preferred method of overriding gethashcode?

As of .NET 4.7 the preferred method of overriding GetHashCode () is shown below. If targeting older .NET versions, include the System.ValueTuple nuget package. In terms of performance, this method will outperform most composite hash code implementations.

What happens if the gethashcode () method is equal to equals?

The GetHashCode() method should reflect the Equals logic; the rules are: if the GetHashCode() is equal, it is not necessary for them to be the same; this is a collision, and Equals will be called to see if it is a real equality or not.

What happens when hashCode returns the same integer?

(-Joshua Bloch) Whenever it (hashcode) 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.