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1. Top results related to overriding the equals method in java

   • overriding the equals method in java

     Top Answer

     Answered May 28, 2019 · 1 votes

     When you write a method invocation expression in Java, a complex set of rules is followed to determine which method will be invoked.

     Basically, the compiler will search for the most specific method that it can find which matches the types of the parameters you are trying to pass in.

     The important thing about these rules is that they make no special provision for methods in Object

     , or any other class. The methods in Object are treated exactly the same as any method you define yourself.

     So, if you are trying to invoke an equals method on an instance of class Stamps, passing in a single instance of Stamps as a parameter, it will find your method:

     boolean equals(Stamps other)-

     This is more specific than the one on Object:

     boolean equals(Object other)-

     ("More specific" is informally defined in the spec thus: any parameter you can pass to a "more specific" method can also be passed to a "less specific" method, but not vice versa).

     so the Java compiler will choose to invoke the equals(Stamps) method.

     However, if you were to change either the first or second (or both) declarations of the variables to be of Object type:

     Object stamp1 = new Stamps("red",10);-

     then the equals(Stamps) method would not be invoked:

     • For Object stamp1, this would be because Java would search the Object type for matching methods. Since only equals(Object) exists on Object, this is the only possible on to invoke.
     • For Object stamp2, this would be because the parameter type of equals(Stamps) would not match, so the only possible method to invoke would be equals(Object).

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   • Overriding the equals method in Java with objects

     Top Answer

     Answered Mar 11, 2020 · 1 votes

     Every Object in Java has hashCode() method which returns an int (a representation of the object).

     In your case you want to compare licencePlate hashCodes such as:

     @Overridepublic boolean equals(Object o) {- if (o == this) return true; if (!(o instanceof Car)) return false; Car that = (Car) o; return Objects.equals(this.hashCode(), that.hashCode());}@Overridepublic int hashCode() { return this.plateNumber.hashCode();}

     Now to compare different fields you will need prime number (this post explains clearly why)

     @Overridepublic int hashCode() { int prime = 31; //Prime1 int hash = 7; //Prime2 hash = prime * hash + (int) id; hash = prime * hash + (plateNumber == null ? 0 : plateNumber.hashCode()); hash = prime * hash + (make == null ? 0 : make .hashCode()); return hash;}

     Useful link (Baeldung Tutorial)

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     2/5

   • Overriding equals method in Java

     Consider the following Java program: 

     Java

     class Complex {    private double re, im;             public Complex(double re, double im) {        this.re = re;        this.im = im;    }} // Driver class to test the Complex classpublic class Main {    public static void main(String[] args) {        Complex c1 = new Complex(10, 15);        Complex c2 = new Complex(10, 15);        if (c1 == c2) {            System.out.println("Equal ");        } else {            System.out.println("Not Equal ");        }    }}

     Output: 

     Not Equal

     The reason for printing “Not Equal” is simple: when we compare c1 and c2, it is checked whether both c1 and c2 refer to same object or not (object variables are always references in Java). c1 and c2 refer to two different objects, hence the value (c1 == c2) is false. If we create another reference say c3 like following, then (c1 == c3) will give true.

     Java

     Complex c3 = c1;  // (c3 == c1) will be true

     So, how do we check for equality of values inside the objects? 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(),.. etc. We can override the equals method in our...

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     3/5

   • Overriding HashMap equals method in Java

     Top Answer

     Answered Oct 23, 2009 · 13 votes

     That's the equals method for HashMap.Entry, not HashMap itself - look at how it's trying to use the reference passed into it as a Map.Entry.

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     4/5

   • Overriding the java equals() method - not working?

     Top Answer

     Answered May 03, 2020 · 334 votes

     In Java, the equals() method that is inherited from Object is:

     public boolean equals(Object other);-

     In other words, the parameter must be of type Object. This is called overriding; your method public boolean equals(Book other) does what is called overloading to the equals() method.

     The ArrayList uses overridden equals() methods to compare contents (e.g. for its contains() and equals() methods), not overloaded ones. In most of your code, calling the one that didn't properly override Object's equals was fine, but not compatible with ArrayList.

     So, not overriding the method correctly can cause problems.

     I override equals the following everytime:

     @Overridepublic boolean equals(Object other){ if (other == null) return false; if (other == this) return true; if (!(other instanceof MyClass)) return false; MyClass otherMyClass = (MyClass)other; ...test other properties here...}

     The use of the @Override annotation can help a ton with silly mistakes.

     Use it whenever you think you are overriding a super class' or interface's method. That way, if you do it the wrong way, you will get a compile error.

     Other Answers

     Answered Jun 02, 2011 · 110 votes

     If you use eclipse just go to the top menu

     Source --> Generate equals() and hashCode()

     Other Answers

     Answered Oct 09, 2008 · 11 votes

     Slightly off-topic to your question, but it's probably worth mentioning anyway:

     Commons Lang has got some excellent methods you can use in overriding equals and hashcode. Check out EqualsBuilder.reflectionEquals(...) and HashCodeBuilder.reflectionHashCode(...). Saved me plenty of headache in the past - although of course if you just want to do "equals" on ID it may not fit your circumstances.

     I also agree that you should use the @Override annotation whenever you're overriding equals (or any other method).

     Check all answers on Stack Overflow

     5/5

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2. www.geeksforgeeks.org › overriding-equals-methodOverriding equals method in Java - GeeksforGeeks

   www.geeksforgeeks.org › overriding-equals-method

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   Jul 29, 2021 · We can override the equals method in our class to check whether two objects have same data or not. Java. class Complex { private double re, im; public Complex(double re, double im) { this.re = re; this.im = im; } @Override. public boolean equals(Object o) { if (o == this) { return true;

3. www.javatpoint.com › override-equals-method-in-javaOverride equals method in Java - Javatpoint

   www.javatpoint.com › override-equals-method-in-java

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   Using the equals () method, we create two objects from the main method by giving identical data and comparing the results. This software returns false because the Object class' equals () method only returns true if the references to the objects are identical. Example code for overriding the equals method:

4. www.baeldung.com › java-override-hashcode-equalsOverriding hashCode() And equals() For Records | Baeldung

   www.baeldung.com › java-override-hashcode-equals

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   • Introduction
   • The hashCode() and equals() Methods
   • Default Implementation of hashCode() and equals() For Record
   • Custom Implementation of hashCode() and equals() For Record
   • When to Override The Default Implementations
   • Conclusion

   Java 14 introduced the idea of a record as an easy and better way to pass around immutable data objects. A record has only the most fundamental methods that a Class has, constructors and getter setters, and is hence a restricted form of a class, similar to an Enum in Java. A record is a plain data carrier, a form of a class used to pass data that i...

   See full list on baeldung.com

   A Java Object class has the equals() and hashCode() methods defined. Since all classes in Java inherit from the Object class, they have the default implementationof the methods as well. The equals() method is meant to assert the equality of two objects, and the default implementation implies that if two objects are of the same identity, they’re equ...

   See full list on baeldung.com

   Any record of type R inherits directly from java.lang.Record. By default, Java provides a default implementation of the two methods for usage. The default equals() implementation obeys the contract of the Object’s equals() method.Additionally, when we create a new record instance by copying all the attributes of another record instance, these two r...

   See full list on baeldung.com

   Java does provide the ability to override the default implementations of the equals() and hashCode() methods. For example, let’s say we decide that it is enough to assert the equality of two Movie records (having several attributes) if the titles and the year of release are identical. In such a scenario, we can choose to override the default implem...

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   Java spec expects any custom implementation of equals() of a record to satisfy the rule that a copy of the record must be equal to the original record. However, since Java records are meant for passing immutable data records around, it is generally safe to go with the default implementations of equals() and hashCode()provided by Java. However, reco...

   See full list on baeldung.com

   In this article, we looked at how records provide us with a default implementation of equals() and hashCode()methods. We also looked at how we can override the default implementations with our custom implementations. We also looked at when we should consider overriding the default behaviors. As usual, all code samples can be found over on GitHub.

   See full list on baeldung.com

   • Author: Bhaskar Ghosh

5. stackoverflow.com › questions › 15175109Why do we have to override the equals() method in Java?

   stackoverflow.com › questions › 15175109

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   Mar 2, 2013 · Java recommends to override equals and hashCode method if equality is going to be defined by logical way or via some business logic: example: many classes in Java standard library does override it e.g. String overrides equals, whose implementation of equals() method return true if content of two String objects are exactly same

   • From the article Override equals and hashCode in Java : Default implementation of equals() class provided by java.lang.Object compares memory lo...
   • This should be enough to answer your question: http://docs.oracle.com/javase/tutorial/java/IandI/objectclass.html The equals() method compares t...
   • .equals() doesn't perform an intelligent comparison for most classes unless the class overrides it. If it's not defined for a (user) class, it beh...
   • The default behavior for java.lang.Object is to compare references, but that's not appropriate for every kind of object. There are things called V...
   • To answer your question, firstly I would strongly recommend looking at the Documentation . Without overriding the equals() method, it will act lik...
   • Let me give you an example that I find very helpful. You can think of reference as the page number of a book. Suppose now you have two pages a and...
   • By default .equals() uses == identity function to compare which obviously doesn't work as the instances test1 and test2 are not the same. == only w...
   • Object.equals() method checks only reference of object not primitive data type or Object value (Wrapper class object of primitive data, simple prim...

6. www.delftstack.com › java › override-equals-in-javaHow to Override equals() in Java | Delft Stack

   www.delftstack.com › java › override-equals-in-java

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   Feb 2, 2024 · 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.

7. People also ask

   How to override equals() method in JavaScript?

   • You can override the equals () method as per your functionality. Suppose you want to compare the object’s own equality condition. Then it is recommended to override the equals (Object obj) method. NOTE: It is always recommended if you are overriding the equals () then you must override the hashCode () method. We’ll discuss it in detail.

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   Should I override equals in Java?

   • Overriding the equals method is necessary if you want to test equivalence in standard library classes (for example, ensuring a java.util.Set contains unique elements or using objects as keys in java.util.Map objects). Note, if you override equals, ensure you honour the API contract as described in the documentation.

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   When to override equals and hashCode method in Java?

   • Java recommends to override equals and hashCode method if equality is going to be defined by logical way or via some business logic: example: many classes in Java standard library does override it e.g. String overrides equals, whose implementation of equals () method return true if content of two String objects are exactly same

   Why do we have to override the equals () method in Java?

   stackoverflow.com/questions/15175109/why-do-we-have-to-override-the-equals-method-in-java

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   What is overriding in Java?

   • In Java, Overriding is when the child class or the subclass has the same execution of method as declared in the parent class. The equals() method compares two strings. If the data of one string object is the same as the other, it returns True value otherwise False.

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8. javagoal.com › equals-method-in-javaequals() method in java & Best practices for Overriding ...

   javagoal.com › equals-method-in-java

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   Mar 25, 2020 · You can override the equals () method as per your functionality. Suppose you want to compare the object’s own equality condition. Then it is recommended to override the equals (Object obj) method. NOTE: It is always recommended if you are overriding the equals () then you must override the hashCode () method.

9. hostman.com › overriding-the-equals-method-in-javaOverriding the equals() Method in Java - hostman.com

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   The equals() method is needed to compare objects with each other. In the standard implementation, the method compares one object with the current object. If the references to them are equal, it returns True; if they are not, it returns False. In turn, hashCode() generates the integer code of the class instance.