IndexOutOfBoundsException: List index is out of range The subsequent elements are shifted to the right. Parameters: index- a position at which the element is to be added.ĭescription: Adds the given element to the list at the given index. Prototype: void add(int index, Object element) ('List after calling clear() method:' + strList) ('Size of list after adding more elements:' + strList.size()) List strList = new ArrayList() // Creating a list The below example will demonstrate size() and clear() method. Throws “UnSupportedException” if the operation is not supported by the list. clearĭescription: Clears the list by removing all the elements of the list. It can also be called length in simple terms. Return Value: int => Number of elements in the list or in other words the length of the list.ĭescription: The size() returns the number of elements or the size of the list. Next, we will discuss these functions along with their examples. Returns a ListIterator starting at the specified index in the list Returns the array representation whose runtime type is the same as a specified array argument Sorts the list element as per the specified comparator to give an ordered list Returns sublist of elements between fromIndex(inclusive), and toIndex(exclusive). List subList (int fromIndex, int toIndex) Retains the element specified in the input collection in the list.Ĭhanges the element at the specified index by setting it to the specified value Removes all elements contained in the specified collection from the list

Removes the element at its first occurrence in the list Removes the element at the specified index Returns the element in the list specified by indexįinds the first occurrence of the input element and returns its indexįinds the last occurrence of the input element in the list and returns its index Returns true of yes.Ĭompares the specified object for equality with elements of the list Inserts the given collection(all elements) to the list at the specified indexĬhecks if the specified element is present in the list and returns true if presentĬhecks if the specified collection (all elements) is part of the list. number of elements in the List or the length of the list.Ĭlears the list by removing all the elements in the listĪdds the given element to the list at the given indexĪdds the given element at the end of the listĪppends the entire given collection to the end of the list That’s all about why we need to override equals and hashcode methods in Java.Returns the size of the list i.e. It is perfectly valid to override hashCode() without overriding equals() as objects with equal hash codes need not be equal. Please note that even though equal objects must have equal hash codes, the reverse is not true. But since the equals() method is not overridden, when the set hashes e2 and iterates through the bucket looking if there is an Employee e such that e2.equals(e) is true, it won’t find any as e2.equals(e1) will be false. If we only override the hashCode() method, both e1 and e2 will hash to the same bucket as they produce the same hash code. Override only hashCode() without overriding equals() method It is worth noting that if the class instance is never used in any hash-based collections, then it doesn’t really matter if hashCode() is overridden or not. Even though both e1 and e2 are equal, they don’t hash to the same bucket, and both reside in the collection as separate keys. Since the default hashCode implementation in the Object class return distinct integers for distinct objects, if only equals() method is overridden, e1 will be placed in some bucket and e2 will be placed in some other bucket as e1.hashCode() != e1.hashCode(). Overriding only equals() method without overriding hashCode() causes the two equal instances to have unequal hash codes, which violates the hashCode contract (mentioned in Javadoc) that clearly says, if two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result. Override only equals() without overriding hashCode() method Now let’s discuss the above program’s behavior if the equals() method is overridden without overriding hashCode(), or vice versa. This is because we have overridden both the equals() and hashCode() method in the Employee class, and both objects now point to the same bucket and hold the same location within the bucket.

As evident from the generated output, the set contains only one Employee object even though two different Employee objects are added.

Equals method map java