Collectors toList() method in Java with Examples

The toList() method of Collectors Class is a static (class) method. It returns a Collector Interface that gathers the input data onto a new list. This method never guarantees type, mutability, serializability, or thread-safety of the returned list but for more control toCollection(Supplier) method can be used. This is an un-ordered collector.

Syntax:

public static  Collector<T, ?, R> toList()

where:

  • T: The type of the input elements.
  • Interface Collector<T, A, R>: A mutable reduction operation that accumulates input elements into a mutable result container, optionally transforming the accumulated result into a final representation after all input elements have been processed. Reduction operations can be performed either sequentially or in parallel.
    • T: The type of input elements to the reduction operation.
    • A: The mutable accumulation type of the reduction operation.
    • R: The result type of the reduction operation.
  • toList():- Static method of Collectors class and returns a Collector interface object used to store a group of data onto a list. The Collectors class is under the java.util.streams package.

Return Value: This method returns a Collector which collects all the input elements into a List, in encounter order

Below are the examples to illustrate toList() method in Java:



Example 1:

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// Java code to show the implementation of
// Collectors toList() function
  
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
        // creating a Stream of strings
        Stream<String> s = Stream.of("Geeks",
                                     "for",
                                     "GeeksforGeeks",
                                     "Geeks Classes");
  
        // using Collectors toList() function
        List<String> myList = s.collect(Collectors.toList());
  
        // printing the elements
        System.out.println(myList);
    }
}

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Output:

[Geeks, for, GeeksforGeeks, Geeks Classes]

Example 2:

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// Java code to show the implementation of
// Collectors toList() function
  
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
  
        // creating a Stream of strings
        Stream<String> s = Stream.of("1", "2", "3", "4");
  
        // using Collectors toList() function
        List<String> myList = s.collect(Collectors.toList());
  
        // printing the elements
        System.out.println(myList);
    }
}

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Output:

[1, 2, 3, 4]

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