java-design-patterns/update-method/README.md

---
title: "Update Method Pattern in Java: Enhancing Game Loop Efficiency with Systematic Updates"
shortTitle: Update Method
description: "Explore the Update Method design pattern for Java, ideal for real-time games and applications. Learn how it optimizes performance by updating objects frame-by-frame to maintain synchronized, efficient operations."
category: Behavioral
language: en
tag:
  - Abstraction
  - Data processing
  - Decoupling
  - Event-driven
  - Game programming
  - Polymorphism
---

## Also known as

* Update Mechanism

## Intent of Update Method Design Pattern

The Update Method pattern in Java simulates a collection of independent objects by telling each to process one frame of behavior at a time.

## Detailed Explanation of Update Method Pattern with Real-World Examples

Real-world example

> A real-world example of the Update Method design pattern is a weather monitoring system. In this system, multiple display devices (such as a mobile app, a website widget, and a wall-mounted digital display) need to show the current weather conditions. These displays subscribe to updates from a central weather station, which collects data from various sensors (temperature, humidity, wind speed, etc.). When the weather station detects new data, it triggers an update method that pushes the new information to all subscribed display devices, ensuring they all show the latest weather conditions simultaneously. This ensures that all displays are synchronized and updated without the need for each device to independently check for updates.

In plain words

> The Update Method design pattern processes system object behavior one frame at a time

gameprogrammingpatterns.com says

> The game world maintains a collection of objects. Each object implements an update method that simulates one frame of the object’s behavior. Each frame, the game updates every object in the collection.

## Programmatic Example of Update Method Pattern in Java

The Update Method design pattern is a behavioral pattern that simulates a collection of independent game or application objects by telling each to process one frame of behavior at a time. This pattern is commonly used in game development, where each object in the game world needs to be updated once per frame.

The `World` class represents the game world. It maintains a list of entities (`List<Entity> entities`) and a boolean flag (`isRunning`) to indicate whether the game is running.

```java
public class World {

  protected List<Entity> entities;
  protected volatile boolean isRunning;

  public World() {
    entities = new ArrayList<>();
    isRunning = false;
  }
  // Other properties and methods...
}
```

The `gameLoop` method is the main game loop. It continuously processes user input, updates the game state, and renders the next frame as long as the game is running.

```java
private void gameLoop() {
  while (isRunning) {
    processInput();
    update();
    render();
  }
}
```

The `processInput` method simulates handling user input. In this case, it simply introduces a random time lag to simulate real-life game situations.

```java
private void processInput() {
  try {
    int lag = new SecureRandom().nextInt(200) + 50;
    Thread.sleep(lag);
  } catch (InterruptedException e) {
    LOGGER.error(e.getMessage());
    Thread.currentThread().interrupt();
  }
}
```

The `update` method is where the Update Method pattern is implemented. It iterates over all entities in the game world and calls their `update` method, allowing each entity to process one frame of behavior.

```java
private void update() {
  for (var entity : entities) {
    entity.update();
  }
}
```

The `render` method is responsible for rendering the next frame. In this example, it does nothing as it's not related to the pattern.

```java
private void render() {
  // Does Nothing
}
```

The `run` and `stop` methods are used to start and stop the game loop.

```java
public void run() {
  LOGGER.info("Start game.");
  isRunning = true;
  var thread = new Thread(this::gameLoop);
  thread.start();
}

public void stop() {
  LOGGER.info("Stop game.");
  isRunning = false;
}
```

The `addEntity` method is used to add new entities to the game world.

```java
public void addEntity(Entity entity) {
  entities.add(entity);
}
```

In the `App` class, we can see how the `World` class and its methods are used to create a game world, add entities to it, and start the game loop.

```java
@Slf4j
public class App {

    private static final int GAME_RUNNING_TIME = 2000;

    public static void main(String[] args) {
        try {
            var world = new World();
            var skeleton1 = new Skeleton(1, 10);
            var skeleton2 = new Skeleton(2, 70);
            var statue = new Statue(3, 20);
            world.addEntity(skeleton1);
            world.addEntity(skeleton2);
            world.addEntity(statue);
            world.run();
            Thread.sleep(GAME_RUNNING_TIME);
            world.stop();
        } catch (InterruptedException e) {
            LOGGER.error(e.getMessage());
        }
    }
}
```

Console output:

```
14:46:33.181 [main] INFO com.iluwatar.updatemethod.World -- Start game.
14:46:33.280 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 1 is on position 11.
14:46:33.281 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 2 is on position 71.
14:46:33.452 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 1 is on position 12.
14:46:33.452 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 2 is on position 72.
14:46:33.621 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 1 is on position 13.
14:46:33.621 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 2 is on position 73.
14:46:33.793 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 1 is on position 14.
14:46:33.793 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 2 is on position 74.
14:46:33.885 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 1 is on position 15.
14:46:33.885 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 2 is on position 75.
14:46:34.113 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 1 is on position 16.
14:46:34.113 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 2 is on position 76.
14:46:34.324 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 1 is on position 17.
14:46:34.324 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 2 is on position 77.
14:46:34.574 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 1 is on position 18.
14:46:34.575 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 2 is on position 78.
14:46:34.730 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 1 is on position 19.
14:46:34.731 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 2 is on position 79.
14:46:34.803 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 1 is on position 20.
14:46:34.803 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 2 is on position 80.
14:46:34.979 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 1 is on position 21.
14:46:34.979 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 2 is on position 81.
14:46:35.045 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 1 is on position 22.
14:46:35.046 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 2 is on position 82.
14:46:35.187 [main] INFO com.iluwatar.updatemethod.World -- Stop game.
14:46:35.288 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 1 is on position 23.
14:46:35.289 [Thread-0] INFO com.iluwatar.updatemethod.Skeleton -- Skeleton 2 is on position 83.
```

This is a basic implementation of the Update Method pattern. In a real-world application, the `Entity` class would likely have additional methods and properties, and the `update` method would contain more complex logic to simulate the entity's behavior.

## When to Use the Update Method Pattern in Java

Update Method works well when:

* Typically applied in scenarios where multiple objects need synchronous updates without the overhead of manual synchronization, making it a go-to for advanced Java developers.
* The application has a number of objects or systems that need to run simultaneously.
* Each object’s behavior is mostly independent of the others.
* The objects need to be simulated over time.

## Real-World Applications of Update Method Pattern in Java

* Real-time games and data processing applications where world objects need to be updated once per frame.

## Benefits and Trade-offs of Update Method Pattern

Benefits:

* Each entity encapsulates its own behavior
* Makes it easy to add and remove entities
* Keeps the main loop uncluttered

Trade-offs:

* Increases complexity due to yielding control every frame
* The state needs to be stored to enable resuming updates after each frame
* Entities are simulated each frame, but they are not truly concurrent

## Related Java Design Patterns

* [Component](https://java-design-patterns.com/patterns/component/): Often used in game development to allow entities to be composed of various components, each potentially having its own update method.
* [Game Loop](https://java-design-patterns.com/patterns/game-loop/): Continuously updates game state and renders the game, which may include the Update Method for various game objects.

## References and Credits

* [Game Programming Patterns](https://amzn.to/3wLTbvr)
* [Game Programming Patterns - Update Method](http://gameprogrammingpatterns.com/update-method.html)