Java set value to string

Set in Java

The set interface is present in java.util package and extends the Collection interface. It is an unordered collection of objects in which duplicate values cannot be stored. It is an interface that implements the mathematical set. This interface contains the methods inherited from the Collection interface and adds a feature that restricts the insertion of the duplicate elements. There are two interfaces that extend the set implementation namely SortedSet and NavigableSet.

In the above image, the navigable set extends the sorted set interface. Since a set doesn’t retain the insertion order, the navigable set interface provides the implementation to navigate through the Set. The class which implements the navigable set is a TreeSet which is an implementation of a self-balancing tree. Therefore, this interface provides us with a way to navigate through this tree.

Declaration: The Set interface is declared as:

public interface Set extends Collection

Creating Set Objects

Since Set is an interface, objects cannot be created of the typeset. We always need a class that extends this list in order to create an object. And also, after the introduction of Generics in Java 1.5, it is possible to restrict the type of object that can be stored in the Set. This type-safe set can be defined as:

// Obj is the type of the object to be stored in Set Set set = new HashSet ();

Let us discuss methods present in the Set interface provided below in a tabular format below as follows:

Method	Description
add(element)	This method is used to add a specific element to the set. The function adds the element only if the specified element is not already present in the set else the function returns False if the element is already present in the Set.
addAll(collection)	This method is used to append all of the elements from the mentioned collection to the existing set. The elements are added randomly without following any specific order.
clear()	This method is used to remove all the elements from the set but not delete the set. The reference for the set still exists.
contains(element)	This method is used to check whether a specific element is present in the Set or not.
containsAll(collection)	This method is used to check whether the set contains all the elements present in the given collection or not. This method returns true if the set contains all the elements and returns false if any of the elements are missing.
hashCode()	This method is used to get the hashCode value for this instance of the Set. It returns an integer value which is the hashCode value for this instance of the Set.
isEmpty()	This method is used to check whether the set is empty or not.
iterator()	This method is used to return the iterator of the set. The elements from the set are returned in a random order.
remove(element)	This method is used to remove the given element from the set. This method returns True if the specified element is present in the Set otherwise it returns False.
removeAll(collection)	This method is used to remove all the elements from the collection which are present in the set. This method returns true if this set changed as a result of the call.
retainAll(collection)	This method is used to retain all the elements from the set which are mentioned in the given collection. This method returns true if this set changed as a result of the call.
size()	This method is used to get the size of the set. This returns an integer value which signifies the number of elements.
toArray()	This method is used to form an array of the same elements as that of the Set.

Illustration: Sample Program to Illustrate Set interface

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Java Set to String

A quick guide to convert set to string instance in java. Examples on HashSet to String and Linkedhashset to String conversions.

1. Overview

2. Set to String Using HashSet.toString()

Use toString() method on the HashSet or LinkedHashSet instance. This method returns the string representation of Set objects.

import java.util.HashSet; import java.util.LinkedHashSet; import java.util.Set; public class SetToStringExample < public static void main(String[] args) < SethashSet = new HashSet<>(); hashSet.add("java"); hashSet.add("c++"); hashSet.add("python"); String str1 = hashSet.toString(); System.out.println("hashset in string - " + str1); Set linkedHashSet = new LinkedHashSet<>(); linkedHashSet.add("javascript"); linkedHashSet.add("typescript"); String str2 = linkedHashSet.toString(); System.out.println("linkedhashset in string - " + str2); > >

hashset in string - [c++, python, java] linkedhashset in string - [javascript, typescript]

In the output, the string form of set is with comma and square brackets. we can use replaceAll() method on the toString() result to remove the unwanted characters and to separate them by empty space.

String str1 = hashSet.toString(); str1 = str1.replaceAll("\\,|\\[|\\]|\\s", " "); System.out.println("hashset in string - " + str1); String str2 = linkedHashSet.toString(); str2 = str2.replaceAll("\\,|\\[|\\]|\\s", " "); System.out.println("linkedhashset in string - " + str2);

hashset in string - c++ python java linkedhashset in string - javascript typescript

3. Set to String using Java 8 API

3.1 Using String.join()

package com.javaprogramto.java8.set.tostring; import java.util.HashSet; import java.util.LinkedHashSet; import java.util.Set; public class Java8SetToStringExample1 < public static void main(String[] args) < SethashSet = new HashSet<>(); hashSet.add("java"); hashSet.add("c++"); hashSet.add("python"); String str1 = String.join(" ", hashSet); System.out.println("String.join() hashset in string - " + str1); Set linkedHashSet = new LinkedHashSet<>(); linkedHashSet.add("javascript"); linkedHashSet.add("typescript"); String str2 = String.join(" ", linkedHashSet); System.out.println("String.join() linkedhashset in string - " + str2); > >

String.join() hashset in string - c++ python java String.join() linkedhashset in string - javascript typescript

System.out.println("With different delimiter"); String str3 = String.join("**", hashSet); System.out.println("String.join() hashset to string - " + str3); String str4 = String.join("^^", linkedHashSet); System.out.println("String.join() linkedhashset to string - " + str4);

With different delimiter String.join() hashset to string - c++**python**java String.join() linkedhashset to string - javascript^^typescript

3.2 Using Collectors.joining()

In java 8 streams, joining() method is added as part of the collectors class. After doing all stream intermediate operations, at the end we need to use the reduction operation using collect() method.

package com.javaprogramto.java8.set.tostring; import java.util.HashSet; import java.util.LinkedHashSet; import java.util.Set; import java.util.stream.Collectors; public class Java8SetToStringExample2 < public static void main(String[] args) < SethashSet = new HashSet<>(); hashSet.add("java"); hashSet.add("c++"); hashSet.add("python"); String str1 = hashSet.stream().collect(Collectors.joining(":", "")); System.out.println("Collectors.joining() hashset in string - " + str1); Set linkedHashSet = new LinkedHashSet<>(); linkedHashSet.add("javascript"); linkedHashSet.add("typescript"); String str2 = linkedHashSet.stream().collect(Collectors.joining(":", "")); System.out.println("Collectors.joining() linkedhashset in string - " + str2); > >

Collectors.joining() hashset in string — Collectors.joining() linkedhashset in string —

4. Set to String — Using Apache Commons

We can also convert HashSet to string with help of the apache commons StringUtils class join() method. This join() method takes the delimiter.

import java.util.HashSet; import java.util.Set; import org.apache.commons.lang3.StringUtils; public class ApacheCommonsSetToStringExample < public static void main(String[] args) < SethashSet = new HashSet<>(); hashSet.add("list"); hashSet.add("set"); hashSet.add("map"); String str1 = StringUtils.join(hashSet); System.out.println("with default delimiter"); System.out.println("hashset in string - " + str1); String str2 = StringUtils.join(hashSet, ":"); System.out.println("with custom delimiter"); System.out.println("hashset in string - " + str2); > >

with default delimiter hashset in string - [set, list, map] with custom delimiter hashset in string - set:list:map

5. Conclusion

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A quick guide to convert set to string instance in java. Examples on HashSet to String and Linkedhashset to String conversions.

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