Will ArrayList allow duplicates?

ArrayList allows duplicate values in its collection. On other hand duplicate elements are not allowed in Hashset.

tutorialspoint.com - Difference between ArrayList and HashSet in Java - Tutorialspoint

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HashSet and ArrayList both are some of the most important classes of the Java Collection framework.

The following are the important differences between ArrayList and HashSet.

Sr. No. Key ArrayList HashSet 1 Implementation ArrayList is the implementation of the list interface. HashSet on the other hand is the implementation of a set interface. 2 Internal implementation ArrayList internally implements array for its implementation. HashSet internally uses Hashmap for its implementation. 3 Order of elements ArrayList maintains the insertion order i.e order of the object in which they are inserted. HashSet is an unordered collection and doesn't maintain any order. 4 Duplicates ArrayList allows duplicate values in its collection. On other hand duplicate elements are not allowed in Hashset. 5 Index performance ArrayList uses index for its performance i.e its index based one can retrieve object by calling get(index) or remove objects by calling remove(index) HashSet is completely based on object also it doesn't provide get() method. 6 Null Allowed Any number of null value can be inserted in arraylist without any restriction. On other hand Hashset allows only one null value in its collection,after which no null value is allowed to be added.

Example of ArrayList vs Hashset

JavaTester.java

Live Demo

import java.io.*; import java.util.*; public class JavaTester { public static void main(String[] args) throws IOException{ int n = 5; List al = new ArrayList<>(n); for (int i = 1; i <= n; i++) { al.add(i); } System.out.println(al); al.remove(3); System.out.println(al); for (int i = 0; i < al.size(); i++) { System.out.print(al.get(i) + " "); } } }

Output

[1, 2, 3, 4, 5] [1, 2, 3, 5] 1 2 3 5

Example

JavaTester.java

import java.util.HashSet; import java.util.Set; public class JavaTester { public static void main(String[] args){ Set hs = new HashSet<>(); hs.add(1); hs.add(2); hs.add(3); hs.add(4); hs.add(4); for (Integer temp : hs) { System.out.print(temp + " "); } } }

Output

1 2 3 4

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Why are Python sets so fast?

But in the case of searching for an element in a collection, sets are faster because sets have been implemented using hash tables. So basically Python does not have to search the full set, which means that the time complexity in average is O(1).

stackoverflow.com - What makes sets faster than lists? - python - Stack Overflow

Sets are implemented using hash tables. Whenever you add an object to a set, the position within the memory of the set object is determined using the hash of the object to be added. When testing for membership, all that needs to be done is basically to look if the object is at the position determined by its hash, so the speed of this operation does not depend on the size of the set. For lists, in contrast, the whole list needs to be searched, which will become slower as the list grows. This is also the reason that sets do not preserve the order of the objects you add. Note that sets aren't faster than lists in general -- membership test is faster for sets, and so is removing an element. As long as you don't need these operations, lists are often faster.

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Can you cancel Simply Piano at any time?

REFUND POLICY If you are not satisfied with any of our programs for any reason, you can cancel your membership. However, NO refunds are available.

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