Java add hashset to hashset

Class HashSet

Type Parameters: E — the type of elements maintained by this set All Implemented Interfaces: Serializable , Cloneable , Iterable , Collection , Set Direct Known Subclasses: JobStateReasons , LinkedHashSet

This class implements the Set interface, backed by a hash table (actually a HashMap instance). It makes no guarantees as to the iteration order of the set; in particular, it does not guarantee that the order will remain constant over time. This class permits the null element.

This class offers constant time performance for the basic operations ( add , remove , contains and size ), assuming the hash function disperses the elements properly among the buckets. Iterating over this set requires time proportional to the sum of the HashSet instance’s size (the number of elements) plus the «capacity» of the backing HashMap instance (the number of buckets). Thus, it’s very important not to set the initial capacity too high (or the load factor too low) if iteration performance is important.

Note that this implementation is not synchronized. If multiple threads access a hash set concurrently, and at least one of the threads modifies the set, it must be synchronized externally. This is typically accomplished by synchronizing on some object that naturally encapsulates the set. If no such object exists, the set should be «wrapped» using the Collections.synchronizedSet method. This is best done at creation time, to prevent accidental unsynchronized access to the set:

Set s = Collections.synchronizedSet(new HashSet(. ));

The iterators returned by this class’s iterator method are fail-fast: if the set is modified at any time after the iterator is created, in any way except through the iterator’s own remove method, the Iterator throws a ConcurrentModificationException . Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.

This class is a member of the Java Collections Framework.

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How to Merge two HashSets in Java

In this article we will discuss how to merge two HashSets.

HashSet provides a member function addAll() i.e.

public boolean addAll(Collection c)

It provides a functionality to add a collection into to a HashSet. But this Collection should be of Same Type as of HashSet or of its Base Class.

How addAll() works

It will iterate over the given Collection one by one and add each element individually in the Hashset. Also, if it has added any element then it will return true else returns false.

Frequently Asked:

Let’s see how to merge to HashSets i.e.

package com.thispointer.java.collections.hashsets; import java.util.ArrayList; import java.util.Arrays; import java.util.HashSet; import java.util.Iterator; public class Example3 < public static void main(String[] args) < // Create a new HashSet of String objects HashSetsetOfStrs1 = new HashSet<>(); // Adding elements in HashSet setOfStrs1.add("hello"); setOfStrs1.add("abc"); setOfStrs1.add("time"); setOfStrs1.add("Hi"); System.out.println("setOfStrs1 = " + setOfStrs1); // Create a new HashSet of String objects HashSet setOfStrs2 = new HashSet<>(); // Adding elements in HashSet setOfStrs2.add("this"); setOfStrs2.add("that"); setOfStrs2.add("there"); System.out.println("setOfStrs2 = " + setOfStrs2); // Merge Set 2 in Set 1 boolean bResult = setOfStrs1.addAll(setOfStrs2); if(bResult) < System.out.println("Merging of Set 1 & Set 2 Successfull"); >System.out.println("setOfStrs1 = " + setOfStrs1); > >

setOfStrs1 = [Hi, abc, hello, time] setOfStrs2 = [that, there, this] Merging of Set 1 & Set 2 Successfull setOfStrs1 = [Hi, that, abc, there, this, hello, time]

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How to Merge two HashSets in Java

The HashSet class implements the Set interface and is backed up by a HashMap instance that acts as a hash table. In this class, the null element is appropriate. If the Hash function correctly distributes the elements between the buckets, the class also provides continuous time for simple operations such as adding, removing, containing, and sizing.

Given two hashsets ,the task is to merge two hashsets in java

stringset1 = [BTechGeeks, this, is, hello] stringset2 = [Java, a, Popular, is, Programming Language]

After merging two hashsets stringset1 = [Java, a, BTechGeeks, Popular, this, is, Programming Language, hello]

Merge two HashSets in Java

1)addAll() function

This method attaches to the end of this list all the elements in the collection in order to return it to the specified Iterator. If the specified collection is modified during the operation the behaviour of this operation is not determined (implies that the behaviour of this call is undefined if the specified collection is this list, and this list is nonempty).

public boolean addAll(Collection c)

: This is the group of elements that will be added to the list.

It returns true if the specified list's elements are appended and the list changes.

2)Merging two hashsets

addAll will iterate through the given Collection one at a time, adding each element to the Hashset individually. Furthermore, if it has added any element, it will return true otherwise, it will return false.

Below is the implementation:

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Copy HashSet in Java Example (append)

This example shows how to copy HashSet to another HashSet in Java. The example also shows how to append one HashSet to another using the addAll method.

How to copy HashSet to another HashSet in Java?

There are several ways using which you can copy one HashSet to another as given below.

1. Using constructor

You can use the below given HashSet constructor to copy the set object.

This HashSet constructor accepts the Collection object and creates a new HashSet object containing all the elements of the specified collection.

2. Using the addAll method

We can also use the addAll method of the HashSet class to copy.

The addAll method adds all the elements of the specified collection object to this set object.

3. Using the clone method

We can also use the clone method of the HashSet class to clone the HashSet object.

The clone method creates a shallow copy of the HashSet object and returns it.

Important Note:

All of the above given approaches only copies the element object reference only. None of the methods given above will deep copy the HashSet object. In order words, only the reference to the element objects are copied, not the actual objects.

The copied HashSet elements still point to the original object. That means, if you change the actual element object, the change will be reflected in both the HashSet objects. In order to understand this, let’s have a look at the below example.

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