Hashset to arraylist in java

Moving data from a HashSet to ArrayList in Java

My code right now has three items within that HashSet array with the ability to add more items through an EditText that captures the user input and stores it in the HashSet. Since extends , you can pass the whole to the constructor: You can view the official tutorial on here: Oracle: Java Collections And more specifically: Set Implementations Question: I want to make ArrayList of HashSet and use it.

Moving data from a HashSet to ArrayList in Java

I have the following Set in Java:

Set < Set> SetTemp = new HashSet < Set>(); 

and I want to move its data to an ArrayList :

ArrayList < ArrayList< String >> List = new ArrayList < ArrayList< String >>); 

Is it possible to do that ?

Moving Data HashSet to ArrayList

Set userAllSet = new HashSet(usrAllTemp); List usrAll = new ArrayList(userAllSet); 

Here usrAllTemp is an ArrayList , which has some values. Same Way usrAll(ArrayList) getting values from userAllSet(HashSet) .

Set> setTemp = new HashSet> (); List> list = new ArrayList> (); for (Set subset : setTemp) < list.add(new ArrayList(subset)); > 

Note: you should start variable names in small caps to follow Java conventions.

You can use the Stream and collector to do this, I hope it is the easiest way

listname = setName.stream().collect(Collectors.toList()); 

Set gamesInstalledTemp = new HashSet < Set>(); List gamesInstalled = new ArrayList<>(); gamesInstalled.addAll(gamesInstalledTemp); 

HashSet in Java, HashSet doesn’t maintain the insertion order. Here, elements are inserted on the basis of their hashcode. HashSet is the best approach for search operations. The initial default capacity of HashSet is 16, and the load factor is 0.75. Difference between List and Set. A list can contain duplicate elements whereas Set …

Using HashSet for duplicate check and convert it back to List

The following code checks for the duplicates using List

public List getGroupMembers() < final Listpersons = new ArrayList(groupMembers.size()); for (GroupMember member : groupMembers) < if (member.getPerson() != null && !member.getPerson().isDeleted()) < persons.add(member.getPerson()); for (int i = 0; i < persons.size(); i++) < for (int j = i + 1; j < persons.size(); j++) < if (persons.get(i).equals(persons.get(j))) < persons.remove(j); i = 0; >> > > > return persons; > **Now for checking the duplicity I have to use Set Collection and convert it to List 

for that I have made the changes as below**

public List getGroupMembers() < final Listpersons = new ArrayList(groupMembers.size()); final HashSet setPersons = new HashSet (); for (GroupMember member : groupMembers) < if (member.getPerson() != null && !member.getPerson().isDeleted()) < setPersons.add(member.getPerson()); persons.addAll(setPersons); >> return persons; > 

However above code doesnt work as expected, please suggest

Removing duplicates from a list is a one-line operation:

persons = new ArrayList(new LinkedHashSet(persons)); 

Using a LinkedHashSet instead of a HashSet will preserve order.

Of course you’d have to remove the final modifier from the variable declaration of persons , but you should anyway because it isn’t necessary and just creates «code noise».

Your code does not eliminate duplicates because it only adds items to setPersons , but never checks it for the presence of a person that you are about to add to the set (and to the list). You should also be adding to the list a single person at a time, not all persons that you have found so far.

Add code that verifies that the person is not in the set already to fix this problem, like this:

Person p = member.getPerson(); if (p != null && !p.isDeleted() && setPersons.add(p))

Note how setPersons.add(p) is used in the if condition. Set’s add returns true if the set did not already contain the member, so the above code makes sure that the person will not be added to the list more than once.

for (GroupMember member : groupMembers) 

This should work, but I cannot test it right now.

public List getGroupMembers() < HashSetsetPersons = new HashSet(); for (GroupMember member : groupMembers) < if (member.getPerson() != null && !member.getPerson().isDeleted()) < setPersons.add(member.getPerson()); >> return new ArrayList(setPersons); > 

Since Set extends Collection , you can pass the whole HashSet to the ArrayList constructor:

/** * Constructs a list containing the elements of the specified collection, * in the order they are returned by the collection's iterator. */ ArrayList(Collection c) 

You can view the official tutorial on Collections here: Oracle: Java Collections

And more specifically: Set Implementations

Converting ArrayList to Hashset in java, I have used a map data structure to store and update the words and their respective frequencies As per your requirement: Each word should be counted just once even though they appear multiple times in a single line.. Iterate over the each line: Store all the words in the set. Now just iterate over this set …

How to make ArrayList of hashset in java?

I want to make ArrayList of HashSet and use it.

**My Problem:**

I will get an Integer N as an user input.
I have to make a hashset and put some values in it.
Then add it to ArrayList and above step is to be done N times.
After it I have to check whether a element is present in the first/second/third/. or Nth hashset in ArrayList.

To check value in which hashset is also given by user.
I dont have to convert my arraylist to hashset either I have to make ArrayList to hashset.

Just make an ArrayList of HashSets :

ArrayList> list = new ArrayList>(); 

Then create HashSets, fill them, and put them in your ArrayList normally.

HashSet set = new HashSet(); set.add(1); set.add(whateverIntValue); list.add(set); 

You can then get the nth HashSet of your list using list.get(n) .

List> sets = new ArrayList<>(); sets.add(someSet()); sets.add(someSet()); sets.add(someSet()); Set someSet() < Setset = new Hashset<>(); Collections.addAll(set, 2, 3, 5, 7, 11); return set; > 

This makes a distinction between specification / interface of variables an method parameters and results, and implementation / implementing class.

So you can change the implementation, say to a sorted TreeSet without pain.

Java — Using HashSet to store a text file and read from it, You want to use crime.contains (search). The revised code would look somewhat like this: // Read the file using whitespace as a delimiter (default) // so that the input will be split into words Scanner file = new Scanner (new File («crime_and_punishment.txt»)); Set crime = new HashSet<> (); // For each …

Display my HashSet to a listVIew

I am trying to display my HashSet array to a ListView so that I can click on a cell and display an alert.

My code right now has three items within that HashSet array with the ability to add more items through an EditText that captures the user input and stores it in the HashSet.

I would like to know if there is a way to take the HashSet items and display them to a listview. I believe the list view allows me to click on a cell and display additional random info through an alert.

public class MainActivity extends Activity < Button aButton; // Global Scope Button sButton; TextView text2; EditText eText; HashSetlist = new HashSet(); @Override protected void onCreate(Bundle savedInstanceState) < super.onCreate(savedInstanceState); setContentView(R.layout.new_layout); aButton = (Button) this.findViewById(R.id.button1); text2 = (TextView) this.findViewById(R.id.textView1); aButton.setOnClickListener(new OnClickListener() < @Override public void onClick(View v) < list.add("Books"); list.add("Newspapers"); list.add("Magazines"); String listString = ""; for (String s : list) < listString += s + " - "; >text2.setText(listString); > >); sButton = (Button) this.findViewById(R.id.button2); eText = (EditText) this.findViewById(R.id.editText1); sButton.setOnClickListener(new OnClickListener() < @Override public void onClick(View view) < //Log.v("EditText", eText.getText().toString()); if( !list.add(eText.getText().toString()) ) < System.out.println("Not Unique Item"); Toast.makeText(getApplicationContext(), "Already Saved!",Toast.LENGTH_LONG).show(); >else < System.out.println("Unique Entry Added"); Toast.makeText(getApplicationContext(), "Saved To Items.", Toast.LENGTH_LONG).show(); >> >); > > 

The problem with HashSet is sets by definition have no order, so it doesn’t make much sense to allow direct coupling with a ListView. But it is easy to convert a HashSet into an ArrayList, like so:

List list = new ArrayList(hashset); 

Java HashSet, A HashSet is a collection of items where every item is unique, and it is found in the java.util package: Example. Create a HashSet object called cars that will store strings: import java.util.HashSet; // Import the HashSet class HashSet cars = new HashSet();

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Convert Set to List in Java and Vice-versa

In Java, List and Set are Collections types to store elements. List is an index-based ordered collection, and Set is an unordered collection. List allows duplicate elements, but Set contains only unique elements. Both collection types are quite different and have their own usecases.

In this Java tutorial, Learn to convert a specified Set to a List. Also, learn to reverse convert List to Set, a useful method to remove duplicate elements from a list.

We will be using the following Set to List type in different ways.

1.1. Using List Constructor

To convert a given Set to a List, we can use the ArrayList constructor and pass HashSet as the constructor argument. It will copy all elements from HashSet to the newly created ArrayList.

ArrayList arrayList = new ArrayList(set); Assertions.assertEquals(3, arrayList.size());

Another useful method to get a List with Set elements is to create an empty list instance and use its addAll() method to add all the elements of the Set to List.

ArrayList arrayList = new ArrayList<>(); arrayList.addAll(set); Assertions.assertEquals(3, arrayList.size());

First, convert the Set to Stream, and then collect the Stream elements to List.

List list = set.stream().toList(); Assertions.assertEquals(3, list.size());

We might need to create a HashSet from a specified ArrayList when we want to remove duplicates from the list because sets do not allow duplicate items.

Let us begin with creating a List instance, and then we will convert it to the Set. The list contains 7 items, but only 4 unique items. So the Set size must be 4 in each method.

List list = List.of(1, 2, 3, 3, 3, 5, 5);

Similar to the previous example, we can use the constructor HashSet(collection) to convert to initialize a HashSet with the items from the ArrayList.

Set set = new HashSet(list); Assertions.assertEquals(4, set.size());

The Set.addAll(list) adds all of the elements in the specified collection to this set if they’re not already present.

Set set = new HashSet(); set.addAll(list); Assertions.assertEquals(4, set.size());

Similar to the previous section, we can convert a set to list using the Stream as follows:

Set set = list.stream().collect(Collectors.toSet()); Assertions.assertEquals(4, set.size());

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Convert HashSet to an ArrayList (List) in Java with Example

In this tutorial, we will be learning how to convert a HashSet to ArrayList (List). I have already shared the 5 difference between HashSet and ArrayList in Java with example.

According to Oracle docs, we will use the ArrayList constructor to convert the HashSet to ArrayList object. The syntax of the ArrayList constructor is given below:

new ArrayList(Collection c) 

where we pass HashSet to the Collection c and it will convert to the ArrayList.

Convert HashSet to ArrayList (List) in Java Example

In the below Java program, the HashSet object is created. Then the HashSet.add() method is used to add elements to the HashSet object. After that, an ArrayList list is created and it is initialized using the elements of the HashSet using a parameterized constructor.

import java.util.*; class HashSetToArrayList  public static void main(String args[])  // Creating HashSet Object HashSetString> hashset = new HashSetString>(); hashset.add("Mango"); hashset.add("Banana"); hashset.add("Pear"); hashset.add("Apple"); hashset.add("Orange"); // Showing HashSet elements System.out.println("HashSet contains : "+ hashset); // Converting HashSet to ArrayList ListString> list = new ArrayListString>(hashset); // Showing ArrayList elements System.out.println("ArrayList contains :"+list); > > 

HashSet contains : [Apple, Pear, Mango, Orange, Banana]
ArrayList contains :[Apple, Pear, Mango, Orange, Banana]
That’s all for today. Please mention in the comments if you have any questions related to the how to convert HashSet to ArrayList/List in Java with example.

About The Author

Subham Mittal has worked in Oracle for 3 years.
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How to Convert HashSet to ArrayList in Java

In this tutorial we will learn about how to convert HashSet to ArrayList in java. We will see different method for converting HashSet to list java . We will use parameterized Constructor and addAll() method of ArrayList for HashSet to ArrayList conversion .

Example 1 : Convert HashSet to ArrayList Using Parameterized Constructor

In this example, We created HashSet and add elements using add() method . Now we will initialize ArrayList Using Parameterized Constructor with HashSet elements .

import java.util.ArrayList; import java.util.HashSet; import java.util.List; public class HashSetToArraylist < public static void main(String[] args) < //create HashSet HashSethashSet = new HashSet(); //add element into HashSet using add() method hashSet.add("Java"); hashSet.add("Vogue"); hashSet.add("Welcomes"); //print HashSet Element System.out.println("HashSet Elements : "+ hashSet); // Converting HashSet to ArrayList List list = new ArrayList(hashSet); //print ArrayList elements System.out.println("ArrayList Elements :"+list); > >

HashSet Elements : [Java, Vogue, Welcomes] ArrayList Elements :[Java, Vogue, Welcomes]

Example 2 : Convert HashSet to List Using addAll() Method

In this example we will convert hashset to arraylist using addAll() method of List . Firstly we created HashSet then add element into it using add() method . Then we will create list. Now we will add HashSet elements to list using List’s addAll() method .

import java.util.ArrayList; import java.util.HashSet; import java.util.List; public class HashSetToArraylist1 < public static void main(String[] args) < //create HashSet HashSethashSet = new HashSet(); //add element into HashSet using add() method hashSet.add("Java"); hashSet.add("Vogue"); hashSet.add("Welcomes"); //print HashSet Element System.out.println("HashSet Elements : "+ hashSet); //create ArrayList List list = new ArrayList(); //adding HashSet Element to Arraylist list.addAll(hashSet); //print ArrayList elements System.out.println("ArrayList Elements :"+list); > >

HashSet Elements : [Java, Vogue, Welcomes] ArrayList Elements :[Java, Vogue, Welcomes]

Example 3 : Convert HashSet to List Using add() Method

In this approach,we will convert HashSet to ArrayList using for loop . We created HashSet and add elements into it. We also created one list. Now We Iterate HashSet Using for-each loop and one by one element of HashSet will added to list using add() method . Let,s see java program for this approach .

import java.util.ArrayList; import java.util.HashSet; import java.util.List; public class HashSetToArraylist2 < public static void main(String[] args) < //create HashSet HashSethashSet = new HashSet(); //add element into HashSet using add() method hashSet.add("Java"); hashSet.add("Vogue"); hashSet.add("Welcomes"); //print HashSet Element System.out.println("HashSet Elements : "+ hashSet); //create ArrayList List list = new ArrayList(); //add HashSet element to ArrayList one by one using loop for (String element : hashSet) < //add element in to list list.add(element); >//print ArrayList elements System.out.println("ArrayList Elements :"+list); > >

HashSet Elements : [Java, Vogue, Welcomes] ArrayList Elements :[Java, Vogue, Welcomes]

In this tutorial we have learned different method for HashSet to ArrayList conversion . You can learn more java HashSet Example for practice .

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