Java Stream Collectors.toUnmodifiableSet()
October 03, 2020
Collectors.toUnmodifiableSet() example introduced in Java 10.
1. The
Collectors.toUnmodifiableSet() returns a Collector that accumulates the input elements into an unmodifiable Set.
2. The returned
Collector throws NullPointerException for null values.
3. If the input contains duplicate elements, an arbitrary element of the duplicates is preserved.
4. This
Collector is unordered.
5. Find the method declaration from Java doc.
public static <T> Collector<T,?,Set<T>> toUnmodifiableSet()
Example-1
In this example we will create unmodifiable set of integer.Example1.java
package com.concretepage;
import java.util.Arrays;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;
public class Example1 {
public static void main(String[] args) {
Set<Integer> set1 = Stream.of(15, 25, 25, 35, 35)
.collect(Collectors.toUnmodifiableSet());
System.out.println(set1);
Set<Integer> set2 = IntStream.range(20, 25).boxed()
.collect(Collectors.toUnmodifiableSet());
System.out.println(set2);
Set<Integer> set3 = Arrays.asList(20, 30, 40, 40).stream().map(i -> i * 2)
.collect(Collectors.toUnmodifiableSet());
System.out.println(set3);
}
}
[35, 25, 15] [22, 23, 24, 20, 21] [40, 60, 80]
set1.add(40);
Exception in thread "main" java.lang.UnsupportedOperationException
Example-2
In this example we will create unmodifiable set of string.Example2.java
package com.concretepage;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Example2 {
public static void main(String[] args) {
Set<String> set1 = Stream.of("Suresh", "Lakshman", "Bharat")
.collect(Collectors.toUnmodifiableSet());
System.out.println(set1);
Set<String> set2 = Stream.of("Mahesh", "Krishn", "Ram").map(s -> "Sri " + s)
.collect(Collectors.toUnmodifiableSet());
System.out.println(set2);
}
}
[Suresh, Bharat, Lakshman] [Sri Ram, Sri Mahesh, Sri Krishn]
Example-3
In this example we will create unmodifiable set of objects.Example3.java
package com.concretepage;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Example3 {
public static void main(String[] args) {
Set<User> set = Stream.of(new User(101, "Mahesh"), new User(102, "Krishna"))
.collect(Collectors.toUnmodifiableSet());
System.out.println(set);
}
}
class User {
private int id;
private String name;
public User(int id, String name) {
this.id = id;
this.name = name;
}
//Sets and Gets
@Override
public String toString() {
return id + "-" + name;
}
}
[102-Krishna, 101-Mahesh]
