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2 - System.out.println for Debugging

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Let’s jump into 2 - System.out.println for Debugging 😎

Using System.out.println

Robocode runs your robot inside a Java VM, so the standard way to print messages is with System.out.println. These messages show up in the Robocode console window while your robot is running. This is a very useful feature for debugging and understanding what your robot is doing at any moment.

System.out.println("Scanning...");

📘 For full documentation of the System class, including println, see the Java System class documentation.

Why Use println?

Using System.out.println helps you debug by letting you track what your robot is doing at key points. For example:

  • When the robot starts or stops
  • When it sees another robot
  • When it hits a wall
  • When it gets hit by a bullet

This lets you check what your robot is “thinking” and if it’s doing what you intended.

A Full Use Case Example

Let’s say you want your robot to introduce itself and report key events.

Step 1: Create a Name Field

First, define a name in your robot class:

import dev.robocode.tankroyale.botapi.*;
import dev.robocode.tankroyale.botapi.events.*;
 
public class DebugBot extends Bot {
    String name = "Mr Robot";
 
    public DebugBot() {
        super(BotInfo.fromFile("DebugBot.json"));
    }

Step 2: Add println Messages in Key Methods

    @Override
    public void run() {
        System.out.println("Hello! My name is " + name);
        while (true) {
            System.out.println("Turning right and scanning...");
            turnRight(45);
            forward(100);
        }
    }
 
    @Override
    public void onScannedBot(ScannedBotEvent e) {
        System.out.println(name + " saw a robot");
        fire(1);
    }
 
    @Override
    public void onHitByBullet(HitByBulletEvent e) {
        System.out.println(name + " was hit by a bullet from direction: " + e.getBullet().getDirection());
        back(50);
    }
 
    @Override
    public void onHitWall(HitWallEvent e) {
        System.out.println(name + " hit a wall");
        turnLeft(180);
        forward(100);
    }

Output Example

In the Robocode console, you’ll see messages like:

Hello! My name is Mr Robot
Turning right and scanning...
Mr Robot saw a robot
Mr Robot was hit by a bullet from direction: 45.0
Mr Robot hit a wall

This gives you a real-time log of what’s going on during battle.

Tips for Effective Debugging

  • Be specific in your messages (e.g., include robot name, event type, and values).
  • Use clear and consistent formatting.
  • Temporarily comment out prints if they’re overwhelming.
  • Print variables you think might be causing issues.

Challenge

Try adding System.out.println to other events like onBulletHit, onBulletMissed, and onRobotDeath. See if you can log all actions your robot takes and adjust behavior based on what you learn.

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