Modern Java Grammar

Lambda

Basic Syntax

• curly brackets '{}' are optional if there is only one statement.

(parameters) -> { statements; }

Examples
Using a for-loop

import java.util.ArrayList;
import java.util.List;

public class LambdaExample {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");

        // Using lambda expression without curly brackets
        names.forEach(name -> System.out.println(name));
    }
}

Simple math calculations

// With curly brackets and return statement
MyMathOperation add = (a, b) -> {
    return a + b;
};

// Without curly brackets and return statement
MyMathOperation addSimple = (a, b) -> a + b;

Stream

Java library that helps managing sequences of elements.
filter: filters out elements based on a certain condition
collect: put elements together into a list

💡Collectors is a utility class provided by the Java Standard Library, specifically in the java.util.stream package. The Collectors class provides various static methods that can be used to accumulate the elements of a stream into a collection, or perform other types of reduction operations.💡

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class StreamExample {
    public static void main(String[] args) {
        // Create a list of integers
        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

        // Use stream to filter even numbers and collect them into a new list
        List<Integer> evenNumbers = numbers.stream()
        									// Intermediate operation: filter even numbers
                                           .filter(n -> n % 2 == 0)
                                           // Terminal operation: collect to a list
                                           .collect(Collectors.toList());

        System.out.println("Even Numbers: " + evenNumbers);
    }
}

map: Transforms elements. For example, making all names all caps.
forEach: Performs an action for each element of the stream

import java.util.Arrays;
import java.util.List;

public class StreamOperationsExample {
    public static void main(String[] args) {
        List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "David");

        // Use stream to convert all names to uppercase and print them
        names.stream()
        	  // Intermediate operation: convert each name to uppercase
             .map(String::toUpperCase) 
              // Terminal operation: print each name
             .forEach(System.out::println); 
    }
}

Output

ALICE
BOB
CHARLIE
DAVID

reduce:
The reduce method takes two parameters:

• Identity Value (0): This is the starting value for the reduction, and it acts as an initial value for the accumulator.
• Binary Operator ((a, b) -> a + b): This is a lambda expression that defines how to combine
  two elements of the stream. In this case, it sums two integers.

The reduce operation applies the binary operator iteratively to all elements of the stream, accumulating the result. The final result of the reduction is the sum of all elements, which is stored in the sum variable.

int sum = numbers.stream()
                 .reduce(0, Integer::sum);

Another example

import java.util.Arrays;
import java.util.List;

public class StreamReduceStringExample {
    public static void main(String[] args) {
        // Create a list of strings
        List<String> words = Arrays.asList("Hello", "World", "Java", "Streams");

        // Use reduce to concatenate all strings
        String concatenatedString = words.stream()
                                         .reduce("", (a, b) -> a + " " + b);

        // Print the result
        System.out.println("Concatenated String: " + concatenatedString.trim());
        // Output: "Hello World Java Streams"
    }
}

💡 Why is .trim() is Needed? 💡
In .reduce(), the initial concatenation is with an empty string("") and the word "Hello" with a space (" ") between them. Therefore, there is unnecessary white space in the beginning of the concatenatedString.