Join our newsletter for the latest updates.
Java Program to pass lambda expression as a method argument

Java Program to pass lambda expression as a method argument

In this example, we will learn to pass lambda expression as the method argument in Java.

To understand this example, you should have the knowledge of the following Java programming topics:


Example 1: Define lambda expressions as method parameters

import java.util.ArrayList;

class Main {
    public static void main(String[] args) {
        // create an ArrayList
        ArrayList<String> languages = new ArrayList<>();

        // add elements to the ArrayList
        languages.add("java");
        languages.add("swift");
        languages.add("python");
        System.out.println("ArrayList: " + languages);

        // pass lambda expression as parameter to replaceAll() method
        languages.replaceAll(e -> e.toUpperCase());
        System.out.println("Updated ArrayList: " + languages);
    }
}

Output

ArrayList: [java, swift, python]
Updated ArrayList: [JAVA, SWIFT, PYTHON]

In the above example, we have created an arraylist named languages. Notice the line,

languages.replaceAll(e -> e.toUpperCase());

Here, e -> e.toUpperCase() is a lambda expression. It takes all elements of the arraylist and converts them into uppercase.


Example 2: Pass multiline lambda body as function arguments

import java.util.ArrayList;
import java.util.Arrays;

class Main {
  public static void main(String[] args) {

    // create an ArrayList
    ArrayList<String> languages = new ArrayList<>(Arrays.asList("java", "python"));
    System.out.println("ArrayList: " + languages);

    // call the foEach() method
    // pass lambda as argument fo forEach()
    // reverse each element of ArrayList
    System.out.print("Reversed ArrayList: ");
    languages.forEach((e) -> {

      // body of lambda expression
      String result = "";
      for (int i = e.length()-1; i >= 0 ; i--)
      result += e.charAt(i);
      System.out.print(result + ", ");
    });

  }
}

Output

ArrayList: [java, python]
Reversed ArrayList: avaj, nohtyp,

In the above example, we have created an arraylist languages. Notice the line,

    languages.forEach((e) -> {

      // body of lambda expression
      String result = "";
      for (int i = e.length()-1; i >= 0 ; i--)
      result += e.charAt(i);
      System.out.print(result + ", ");
    });

Here, we are passing lambda expression as an argument to the ArrayList forEach() method. The lambda expression will reverse each element of the arraylist.