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The hash function in Java, used by HashMap and HashSet, is provided by the Object.hashCode() method. Since every class in Java inherits from Object, every object has a hash function. A class can override the default implementation of hashCode() to provide a custom hash function more in accordance with the properties of the object.
Now if the equals method is called for a Button object and there is no such method in the Button class but there is an overridden equals method in Rectangle or Clickable (or both), which method should be eventually called? It is called the "diamond problem" because of the shape of the class inheritance diagram in this situation.
In C#, a class is a reference type while a struct (concept derived from the struct in C language) is a value type. [5] Hence an instance derived from a class definition is an object while an instance derived from a struct definition is said to be a value object (to be precise a struct can be made immutable to represent a value object declaring attributes as readonly [6]).
In object-oriented programming, a covariant return type of a method is one that can be replaced by a "narrower" (derived) type when the method is overridden in a subclass. A notable language in which this is a fairly common paradigm is C++. C# supports return type covariance as of version 9.0. [1]
In Java, this will mean that the method in the derived class will implicitly override the method in the base class, even though that may not be the intent of the designers of either class. To mitigate this, C# requires that if a method is intended to override an inherited method, the override keyword must be specified. Otherwise, the method ...
Primitive wrapper classes are not the same thing as primitive types. Whereas variables, for example, can be declared in Java as data types double, short, int, etc., the primitive wrapper classes create instantiated objects and methods that inherit but hide the primitive data types, not like variables that are assigned the data type values.
a.Equals(b) The == operator defaults to ReferenceEquals, but can be overloaded to perform Equals instead. Common Lisp (eq a b) (equal a b) Erlang: a =:= b: a == b: when a and b are numbers Go: a == b: reflect.DeepEqual(*a, *b) when a and b are pointers Java: a == b: a.equals(b) JavaScript: a === b: a == b
clone() is a method in the Java programming language for object duplication. In Java, objects are manipulated through reference variables, and there is no operator for copying an object—the assignment operator duplicates the reference, not the object. The clone() method provides this missing functionality.