Convert Set of Integer to Set of String in Java 8 and above

This post will discuss how to convert set of Integer to set of string in Java.

We can use Java 8 Stream to convert Set<Integer> to Set<String>. Following are the complete steps:

Convert Set<Integer> to Stream<Integer> using Set.stream().
Convert Stream<Integer> to Stream<String> using Stream.map().
Accumulate Stream<String> into Set<String> using Collectors.toSet().

The following program demonstrates it:

import java.util.Arrays;

import java.util.Set;

import java.util.HashSet;

import java.util.stream.Collectors;

class Main

{

public static void main(String[] args)

{

Set<Integer> ints = new HashSet<>(Arrays.asList(1, 2, 3, 4, 5));

Set<String> items = ints.stream()

.map(String::valueOf)

.collect(Collectors.toSet());

System.out.println(items); // [1, 2, 3, 4, 5]

}

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Following is a generic version of the above program. It passes the method reference as a parameter to the generic function.

import java.util.Arrays;

import java.util.Set;

import java.util.HashSet;

import java.util.function.Function;

import java.util.stream.Collectors;

class Main

{

// Generic method to convert `Set<Integer>` to `Set<String>`

public static <T, U> Set<U> transform(Set<T> set, Function<T, U> function)

{

return set.stream()

.map(function)

.collect(Collectors.toSet());

}

public static void main(String[] args)

{

Set<Integer> ints = new HashSet<>(Arrays.asList(1, 2, 3, 4, 5));

Set<String> items = transform(ints, String::valueOf);

System.out.println(items); // [1, 2, 3, 4, 5]

}

Download Run Code

This is equivalent to:

import java.util.Arrays;

import java.util.HashSet;

import java.util.Set;

import java.util.function.Function;

class Main

{

// Generic method to convert `Set<Integer>` to `Set<String>`

public static <T, U> Set<U> transform(Set<T> set, Function<T, U> function)

{

Set<U> result = new HashSet<>();

for (T t : set) {

U u = function.apply(t);

result.add(u);

}

return result;

}

public static void main(String[] args)

{

Set<Integer> ints = new HashSet<>(Arrays.asList(1, 2, 3, 4, 5));

Set<String> items = transform(ints, String::valueOf);

System.out.println(items); // [1, 2, 3, 4, 5]

}

Download Run Code

That’s all about converting Set of Integer to Set of String in Java 8.

Convert Set of Integer to Set of String in Java 8 and above

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