This is typically accomplished by writing the Equals Object method in terms of the overloaded equality operator, as in the following example. Because Complex is a value type, it cannot be derived from. Therefore, the override to Equals Object method need not call GetType to determine the precise run-time type of each object, but can instead use the is operator in C or the TypeOf operator in Visual Basic to check the type of the obj parameter.
The type of comparison between the current instance and the obj parameter depends on whether the current instance is a reference type or a value type. If the current instance is a reference type, the Equals Object method tests for reference equality, and a call to the Equals Object method is equivalent to a call to the ReferenceEquals method.
Reference equality means that the object variables that are compared refer to the same object. The following example illustrates the result of such a comparison. It defines a Person class, which is a reference type, and calls the Person class constructor to instantiate two new Person objects, person1a and person2 , which have the same value. It also assigns person1a to another object variable, person1b.
As the output from the example shows, person1a and person1b are equal because they reference the same object. However, person1a and person2 are not equal, although they have the same value. If the current instance is a value type, the Equals Object method tests for value equality.
Value equality means the following:. The two objects are of the same type. As the following example shows, a Byte object that has a value of 12 does not equal an Int32 object that has a value of 12, because the two objects have different run-time types.
The values of the public and private fields of the two objects are equal. The following example tests for value equality. It defines a Person structure, which is a value type, and calls the Person class constructor to instantiate two new Person objects, person1 and person2 , which have the same value. As the output from the example shows, although the two object variables refer to different objects, person1 and person2 are equal because they have the same value for the private personName field.
Because the Object class is the base class for all types in the. NET Framework, the Object. Equals Object method provides the default equality comparison for all other types. However, types often override the Equals method to implement value equality. For more information, see the Notes for Callers and Notes for Inheritors sections.
When you call the Equals Object method overload on a class in the Windows Runtime, it provides the default behavior for classes that don't override Equals Object. This is part of the support that the. Classes in the Windows Runtime don't inherit Object , and currently don't implement an Equals Object method.
NET Framework provides the default behavior for these methods. Derived classes frequently override the Object. Equals Object method to implement value equality. When you call the Equals method to test for equality, you should know whether the current instance overrides Object.
Equals and understand how a particular call to an Equals method is resolved. Otherwise, you may be performing a test for equality that is different from what you intended, and the method may return an unexpected value. The following example provides an illustration.
It instantiates three StringBuilder objects with identical strings, and then makes four calls to Equals methods. The first method call returns true , and the remaining three return false. In the first case, the strongly typed StringBuilder. Equals StringBuilder method overload, which tests for value equality, is called.
Because the strings assigned to the two StringBuilder objects are equal, the method returns true. However, StringBuilder does not override Object. Equals Object. Because of this, when the StringBuilder object is cast to an Object , when a StringBuilder instance is assigned to a variable of type Object , and when the Object. Equals Object method is called. Because StringBuilder is a reference type, this is equivalent to passing the two StringBuilder objects to the ReferenceEquals method.
Although all three StringBuilder objects contain identical strings, they refer to three distinct objects. As a result, these three method calls return false. You can compare the current object to another object for reference equality by calling the ReferenceEquals method. When you define your own type, that type inherits the functionality defined by the Equals method of its base type. The following table lists the default implementation of the Equals method for the major categories of types in the.
NET Framework. As part of this article, we are going to discuss the following pointers. In C , as we already discussed every type directly or indirectly inherits from the Object class. So, the Equals virtual method, which has a default implementation within the Object class is also available in every type via inheritance. In the following example, the variables i and j are integers.
In the following example, C1 and C2 are 2 different object reference variables. But both are pointing to the same object. The most important point that you need to keep in mind is reference variables are different from objects. Reference variables are created on the stack and they point to the actual objects which are stored in the heap. Since, C1 and C2 both refer to the same object, the reference equality, and the value equality is true.
Value equality means that two objects contain the same values. In this example, the actual object is only one, so obviously, the values are also equal. Consider the following Java program: Attention reader! Get hold of all the important Java Foundation and Collections concepts with the Fundamentals of Java and Java Collections Course at a student-friendly price and become industry ready.
All classes in Java inherit from the Object class, directly or indirectly See point 1 of this. The Object class has some basic methods like clone , toString , equals ,.. We can override the equals method in our class to check whether two objects have same data or not. We will be covering more about hashCode in a separate post. References: Effective Java Second Edition Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
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