How do you override equals in java

First, this requires detailed knowledge of the super classes - the sub-class must know all instance data and all methods to access them. The downside of this approach is that it is more work and more likely to be wrong in the first place, and less likely to be maintained properly in the second place. Imagine someone else wrote class A and you are simply extending it. By calling the accessor methods of class A in class C's implementation of equals the Class C code is tightly coupled to Class A's implementation.

Now imagine that the person that wrote class A makes changes - how likely are they to realize that class C may be affected by the changes? Even if they notice will they know how to modify Class C's implementation to work with the new class A? As you can see, even a relatively simple change to Class A that should be isolated has now become more complicated and error prone.

How do you solve this issue? Easy Normal Medium Hard Expert. Writing code in comment? Please use ide. Load Comments. What's New. Most popular in Java. If the data of one string object is the same as the other, it returns True value otherwise False. When we override the equals method, it is always recommended to override the hashtag method also. To check whether the values in the objects are equal or not, we use the equals method. We can override this method in the class to check whether the two objects have the same data or not, as the classes in Java are inherited from the object classes only.

I am trying to override equals method in Java. I have a class People which basically has 2 data fields name and age. Now I want to override equals method so that I can check between 2 People objects. But when I write age. Introducing a new method signature that changes the parameter types is called overloading :.

When a method signature remains the identical to that of its superclass, it is called overriding and the Override annotation helps distinguish the two at compile-time:. Without seeing the actual declaration of age , it is difficult to say why the error appears. See What issues should be considered when overriding equals and hashCode in Java? According to Effective Java , Overriding the equals method seems simple, but there are many ways to get it wrong, and consequences can be dire.

The easiest way to avoid problems is not to override the equals method, in which case each instance of the class is equal only to itself. This is the right thing to do if any of the following conditions apply:. Each instance of the class is inherently unique. This is true for classes such as Thread that represent active entities rather than values. The equals implementation provided by Object has exactly the right behavior for these classes. For example, java. Under these circumstances, the equals implementation inherited from Object is ideal.

A superclass has already overridden equals, and the superclass behavior is appropriate for this class. For example, most Set implementations inherit their equals implementation from AbstractSet, List implementations from AbstractList, and Map implementations from AbstractMap.

The class is private or package-private , and you are certain that its equals method will never be invoked. Reflexive: For any non-null reference value x , x. Symmetric: For any non-null reference values x and y , x. Transitive: For any non-null reference values x , y , z , if x.

Consistent: For any non-null reference values x and y , multiple invocations of x. For any non-null reference value x , x. If so, return true. This is just a performance optimization but one that is worth doing if the comparison is potentially expensive. Use the instanceof operator to check if the argument has the correct type. If not, return false.