How to Map Elements Using the Map Method in Java 8

See Java: Tips and Tricks for similar articles.
Looking to improve your Java skills? Check out Webucator’s Java classes.

Imagine you have a collection of temperature readings in Celsius that you need to convert to Fahrenheit. Prior to Java 8 you would be required to iterate through the collection and convert each temperature reading individually. In Java 8, the conversion of each temperature can be done in just one line of code. The key to achieving this goal is to use the map method of the Stream class. This method maps (i.e., translates) each element of a collection based on a given lambda or method reference. To learn how to map elements using the map method, follow these four steps.

  1. Open your text editor and create the Java program that will demonstrate the use of the map method. Type in the following Java statements:
    import java.util.stream.*;
    import java.util.*;
    public class MapElementsWithmapMethod {
    	private static List temperaturesInCelsius=Arrays.asList(-5, 0, 17, 25, 38, 100);
    	public static void main (String args[]) {
    		System.out.println("Current temperature values in Celsius:");
    		temperaturesInCelsius.stream().forEach(System.out::println);
    		System.out.println("Converted temperature values in Fahrenheit:");
    		temperaturesInCelsius.stream().map(temp -> (9 * temp) / 5 + 32).collect(Collectors.toList()).forEach(System.out::println);
    	}
    }
    The stream will be created from the ArrayList that is defined on line 4. Note the Arrays.asList method is used to convert the array of integers to an ArrayList. The map method is passed to a lambda expression that converts the temperature from Celsius to Fahrenheit. The collect method collects the converted elements and applies the Collectors.toList to the elements, producing a new stream. The stream will be printed using the forEach method. I have highlighted the method chain containing the map method below:Java Source for Map Method
  2. Save your file as MapElementsWithmapMethod.java.
  3. Open a command prompt and navigate to the directory containing your new Java program. Then type in the command to compile the source and hit Enter.Compile Program with Map Method
  4. You are ready to test your Java program. Type in the command to run the Java runtime launcher and hit Enter. The output displays the original list of temperatures stored in Celsius followed by the list of temperatures as converted into Fahrenheit by the map method.Run Program with Map Method

Related Articles

  1. How to Check Object Type in Java
  2. How to Create a Jar File in Java
  3. How to Compile Packages in Java
  4. How to Throw an Exception in Java
  5. How to Create an Exception Class in Java
  6. How to Use the super Keyword to Call a Base Class Constructor in Java
  7. How to Use the Comparator.comparing Method in Java 8
  8. How to Use System.in in Java
  9. How to Call an Interface Method in Java
  10. How to Add a Time Zone in the Java 8 Date/Time API
  11. How to Rethrow an Exception in Java
  12. How to Use the instanceof Operator with a Generic Class in Java
  13. How to Instantiate an Object in Java
  14. How to Filter Distinct Elements from a Collection in Java 8
  15. How to Create a Derived Class in Java
  16. How to Skip Elements with the Skip Method in Java 8
  17. How to Create a Java Bean
  18. How to Implement an Interface in Java
  19. How to Compare Two Objects with the equals Method in Java
  20. How to Set PATH from JAVA_HOME
  21. How to Prevent Race Conditions in Java 8
  22. How to Write a Block of Code in Java
  23. How to Display the Contents of a Directory in Java
  24. How to Group and Partition Collectors in Java 8
  25. How to Create a Reference to an Object in Java
  26. How to Reduce the Size of the Stream with the Limit Method in Java 8
  27. How to Write an Arithmetic Expression in Java
  28. How to Format Date and Time in the Java 8 Date/Time API
  29. How to Use Comparable and Comparator in Java
  30. How to Break a Loop in Java
  31. How to Use the this Keyword to Call Another Constructor in Java
  32. How to Write a Unit Test in Java
  33. How to Declare Variables in Java
  34. How to Override Base Class Methods with Derived Class Methods in Java
  35. How to Use Serialized Objects in Java
  36. How to Write Comments in Java
  37. How to Implement Functional Interfaces in Java 8
  38. How to Write Type Parameters with Multiple Bounds in Java
  39. How to Add Type and Repeating Annotations to Code in Java 8
  40. How to Use Basic Generics Syntax in Java
  41. How to Map Elements Using the Map Method in Java 8 (this article)
  42. How to Work with Properties in Java
  43. How to Write while and do while Loops in Java
  44. How to Use the finally Block in Java
  45. How to Write for-each Loops in Java
  46. How to Create a Method in Java
  47. How to Continue a Loop in Java
  48. How to Handle Java Files with Streams
  49. How to Create an Interface Definition in Java
  50. How Default Base Class Constructors Are Used with Inheritance