Iterating Custom Object Lists in Java: Enhanced For Loop and Streams

Introduction

In Java development, working with collections of custom objects is frequent. A common requirement is to iterate over an ArrayList of user-defined classes, such as a Room object.

Enhanced For Loop Syntax

The enhanced for loop, introduced in Java 5, simplifies iteration. For a list of custom objects, the syntax is for (Type variable : collection) { ... }.

For example, with an ArrayList<Room>:

for (Room room : rooms) {
    System.out.println(room.getName());
}

Detailed Code Example

Define a simple Room class:

public class Room {
    private String name;
    private int size;
    // getters and setters
}

Then, iterate:

ArrayList<Room> rooms = new ArrayList<>();
// Assume rooms are added
for (Room room : rooms) {
    if (room.getSize() > 100) {
        System.out.println("Large room: " + room.getName());
    }
}

Other Iteration Techniques

Alternative methods include using an Iterator or Java 8's forEach with streams.

With Iterator:

for (Iterator<Room> i = rooms.iterator(); i.hasNext(); ) {
    Room room = i.next();
    // process room
}

With Java 8 forEach:

rooms.forEach(room -> System.out.println(room.getName()));

Or with method reference:

rooms.forEach(System.out::println);

Conclusion

The enhanced for loop is the most straightforward way to iterate custom object lists in Java. For more advanced operations, Java 8 streams offer functional programming capabilities.