Quick Answer: Why CompareTo () Should Be Consistent To Equals () Method In Java?

How do you write compareTo in Java?

Java String compareTo() method examplepublic class CompareToExample{public static void main(String args[]){String s1=”hello”;String s2=”hello”;String s3=”meklo”;String s4=”hemlo”;String s5=”flag”;System.out.println(s1.compareTo(s2));//0 because both are equal.More items….

Why use .equals instead of == Java?

1) use == to compare primitive e.g. boolean, int, char etc, while use equals() to compare objects in Java. 2) == return true if two reference are of same object. Result of equals() method depends on overridden implementation. 3) For comparing String use equals() instead of == equality operator.

Does TreeSet use compareTo?

That is because TreeSet uses compareTo (or Comparator. compare ) to test whether two elements are equal. … Note that the ordering maintained by a set (whether or not an explicit comparator is provided) must be consistent with equals if it is to correctly implement the Set interface.

Why do we need hashCode?

HashMap and HashSet use the hashcode value of an object to find out how the object would be stored in the collection, and subsequently hashcode is used to help locate the object in the collection.

What is a TreeSet?

TreeSet is one of the most important implementations of the SortedSet interface in Java that uses a Tree for storage. The ordering of the elements is maintained by a set using their natural ordering whether or not an explicit comparator is provided.

Is equal to Java?

The java string equals() method compares the two given strings based on the content of the string. If any character is not matched, it returns false. If all characters are matched, it returns true. The String equals() method overrides the equals() method of Object class.

What is the importance of hashCode () and equals () methods?

Java hashCode() An object hash code value can change in multiple executions of the same application. If two objects are equal according to equals() method, then their hash code must be same. If two objects are unequal according to equals() method, their hash code are not required to be different.

How does a HashMap work?

HashMap in Java works on hashing principles. It is a data structure which allows us to store object and retrieve it in constant time O(1) provided we know the key. In hashing, hash functions are used to link key and value in HashMap.

How does the compareTo () method work?

The compareTo() method compares two strings lexicographically. The comparison is based on the Unicode value of each character in the strings. The method returns 0 if the string is equal to the other string.

Can we override compareTo method?

There are certain rules and important points to remember while overriding compareTo method: 1) CompareTo method must return negative number if current object is less than other object, positive number if current object is greater than other object and zero if both objects are equal to each other.

How is hashCode calculated?

Steps:Calculate hashCode of Key {“sachin”}. It will be generated as 115.Calculate index by using index method it will be 3.Create a node object as : { int hash = 115 Key key = {“sachin”} Integer value = 30 Node next = null }

Does two object will always be equal when their compareTo () method returns zero?

It is recommended that compareTo only returns 0 , if a call to equals on the same objects would return true : The natural ordering for a class C is said to be consistent with equals if and only if e1. compareTo(e2) == 0 has the same boolean value as e1.

What is difference between == equals () and compareTo () method?

equals() checks if two objects are the same or not and returns a boolean. compareTo() (from interface Comparable) returns an integer. It checks which of the two objects is “less than”, “equal to” or “greater than” the other. … Note that equals() doesn’t define the ordering between objects, which compareTo() does.

What is a comparator in Java?

Java Comparator interface is used to order the objects of a user-defined class. This interface is found in java. util package and contains 2 methods compare(Object obj1,Object obj2) and equals(Object element).

What does == mean in Python?

comparison operator== is a comparison operator while = will assign a value to said variable. You can use == to see whether any two items as long they are the same type are equivalent: if a == 2: # Compares whether a is equal to 2 print a.