Java Lambda Expressions forEach Example

This example demonstrates the usage of forEach function with lambda expressions in Java.

Loop a List with forEach + lambda expression

In Java 8, you can loop a List with forEach + lambda expression or method reference.

public static void forEachWithList() {

    final List < Person > items = new ArrayList < > ();
    items.add(new Person(100, "Ramesh"));
    items.add(new Person(100, "A"));
    items.add(new Person(100, "B"));
    items.add(new Person(100, "C"));
    items.add(new Person(100, "D"));

    //lambda
    items.forEach(item - > System.out.println(item.getName()));

    //Output : C
    items.forEach(item - > {
        if ("C".equals(item)) {
            System.out.println(item);
        }
    });

    //method reference
    //Output : A,B,C,D,E
    items.forEach(System.out::println);

    //Stream and filter
    //Output : B
    items.stream()
        .filter(s - > s.getName().equals("Ramesh"))
        .forEach(System.out::println);
}

Please refer to the comments in the above example are self-descriptive.

Loop a Map with forEach and lambda expressions

In Java 8, you can loop a Map with forEach and lambda expressions.

public static void forEachWithMap() {

    // Before Java 8, how to loop map
    final Map < Integer, Person > map = new HashMap < > ();
    map.put(1, new Person(100, "Ramesh"));
    map.put(2, new Person(100, "Ram"));
    map.put(3, new Person(100, "Prakash"));
    map.put(4, new Person(100, "Amir"));
    map.put(5, new Person(100, "Sharuk"));

    //  In Java 8, you can loop a Map with forEach + lambda expression.
    map.forEach((k, p) - > {
        System.out.println(k);
        System.out.println(p.getName());
    });
}

Check out more examples at https://www.javaguides.net/2018/06/guide-to-java-8-foreach-method.html.