It is recommended that compareTo only returns 0 , if a call to equals on the same objects would return true : compareTo(e2) == 0 has the same boolean value as e1. equals(e2) for every e1 and e2 of class C. Note that null is not an instance of any class, and e.
In respect to this, is it possible for equals () to return false even if contents of two objects are same?
4 Answers. In java the method public boolean equals(Object obj) is inherited from the Object. However, the implementation of the method as defined in the Object class is that the equals method will return if and only if the two objects being compared are the same instance.
Additionally, why compareTo () should be consistent to equals () method in Java? This is so because the Map interface is defined in terms of the equals operation, but a map performs all key comparisons using its compareTo (or compare) method, so two keys that are deemed equal by this method are, from the standpoint of the sorted map, equal.
Simply so, what is difference between == equals () and compareTo () method?
compareTo: Compares two strings lexicographically. equals: Compares this string to the specified object. compareTo compares two strings by their characters (at same index) and returns an integer (positive or negative) accordingly. equals() checks if two objects are the same or not and returns a boolean.
Can we override compareTo method?
Override compareTo Method It should return a negative integer(usually -1), if the current triggering object is less than the passed one, and positive integer (usually +1) if greater than, and 0 if equal. compareTo method should throws an exception if the passed object has incompatible type or null.
18 Related Question Answers Found
What is the hashCode () and equals () used for?
Usage of hashCode() and equals() Methods equals(Object otherObject) – As method name suggests, is used to simply verify the equality of two objects. It’s default implementation simply check the object references of two objects to verify their equality.
How do you override equals method?
Therefore, overridden equals() method must have the following properties: Reflexive: x. equals(x) is true . Symmetric: x. equals(y) is true if and only if y. equals(x) . Transitive: if x. equals(y) and y. equals(z) are true , then so is x. equals(z) .
What will happen if two different objects have the same hashCode?
If two different objects have same hashCode, this causes collision in the hash table, because both objects want to be in dame bucket. Each bucket can contain a list of objects with the same hashCode. In HashMap keys along with their associated values are stored in a linked list node in the bucket.
Can two strings have same hashCode?
Yes, it is possible for two Strings to have the same hashcode – If you take a look at the Wikipedia article, you will see that both “FB” and “Ea” have the same hashcode.
How do you override hashCode and equals method?
if a class overrides equals, it must override hashCode. when they are both overridden, equals and hashCode must use the same set of fields. if two objects are equal, then their hashCode values must be equal as well. if the object is immutable, then hashCode is a candidate for caching and lazy initialization.
How do you compare two numbers in Java?
To compare two Numbers in Java you can use the compareTo method from BigDecimal. BigDecimal can hold everything from short until double or BigInteger, so its the perfect class for this. The specific method you suggest would fail, because it’s using equals() inherited from Object .
How do you make two objects equal in Java?
Java determines equality with the equals(Object o) method – two objects a and b are equal iff a. equals(b) and b. equals(a) return true . These two objects will be equal using the base Object definition of equality, so you don’t have to worry about that.
Why do we override equals and hashCode in Java?
28 Answers. You must override hashCode() in every class that overrides equals(). Failure to do so will result in a violation of the general contract for Object. hashCode(), which will prevent your class from functioning properly in conjunction with all hash-based collections, including HashMap, HashSet, and Hashtable.
How do you know if two objects are equal?
If the two objects have the same values, equals() will return true . In the second comparison, equals() checks to see whether the passed object is null, or if it’s typed as a different class. If it’s a different class then the objects are not equal. Finally, equals() compares the objects’ fields.
Can we compare two strings using ==?
When you check (compare) two objects using the == operator it compares the address equality into the string-pool. If the two String objects have the same address references then it returns true , otherwise false . But if you want to compare the contents of two String objects then you must override the equals method.
What is === in Javascript?
=== is the strict equal operator. It only returns a Boolean True if both the operands are equal and of the same type. If a is 2, and b is 4, a === 2 (True) b === 4 (True) a === ‘2’ (False) vs True for all of the following, a == 2 a == “2” 2 == ‘2’
What does += mean in Java?
They perform the operation on the two operands before assigning the result to the first operand. The following are all possible assignment operator in java: 1. += (compound addition assignment operator) 2. -= (compound subtraction assignment operator) 3.
What is comparator in Java?
Comparator Interface in Java with Examples. Comparator interface is used to order the objects of user-defined classes. A comparator object is capable of comparing two objects of two different classes. Following function compare obj1 with obj2.
What is the use of equals method in comparator?
equals() compares another object with the comparator itself for equality. The equals() method is a very low level method in Java and is used all over the place. One example is when a value is used as a key in a hash table, the equals method is used to compare it with another object of its class to match.
What is the difference between equals and compareTo in Java?
compareTo: Compares two strings lexicographically. equals: Compares this string to the specified object. compareTo compares two strings by their characters (at same index) and returns an integer (positive or negative) accordingly.
How does comparator work in Java?
Methods of Java 8 Comparator Interface It compares the first object with second object. It accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator that compares by that sort key. It returns a comparator that compares Comparable objects in natural order.
What is difference between compare and compareTo in Java?
compareTo() is called on one object, to compare it to another object. compare() is called on some object to compare two other objects. The difference is where the logic that does actual comparison is defined. The relationship of the object having this method and its collaborators is different.
How do you override comparison?
Override compare Method All what you need to do is to return an integer, positive if first argument is greater, negative if less than, and 0 if equal. compare method should throws an exception if the passed object has incompatible type or null(same as compareTo method).