A walkthrough of the basic structure
Last updated 8-23-23
OpMode contains the subclass LinearOpMode, meaning that LinearOpMode is actually implemented in terms of OpMode. This is explored more in (coming soon) Which OpMode? Each implemented in terms of the other, but right now this fact is mostly just an excuse to link to both classes in the JavaDoc. They can both do all the same things, but many people find that their different structures cater to different use cases. Keep that in mind - don't get caught up in one! Look at both and determine which is the best to use for each program.
Here is the barebones structure of an OpMode (with Android Studio colorization based on site theme):
package org.firstinspires.ftc.teamcode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.eventloop.opmode.OpMode;
//or @Autonomous
//Change these arguments to change the appearance in the Driver Station
@TeleOp(name="", group="")
public class BoilerPlate_OpMode extends OpMode {
//Declare variables (more specifically class members) here
@Override
public void init() {
//Initialize things here
}
@Override
public void init_loop() {
//loop until Start is pressed
}
@Override
public void start() {
//run once when Start is pressed
}
@Override
public void loop() {
//loop until Stop is pressed
}
@Override
public void stop() {
//run once when Stop is pressed
}
}
That might tell you everything you need to know, but if it doesn't, we're going to walk through it.
OpMode handles more things for you than LinearOpMode does. Notably, calling idle() is not required (it shouldn't be needed in LinearOpMode either because a LinearOpMode runs in its own thread but some sources recommend it) and telemetry is automatically updated without requiring you to call telemetry.update().
package org.firstinspires.ftc.teamcode;
This line tells the compiler that this class is part of the TeamCode package. This is important becuase only TeamCode gets built onto the device, so we need to be in that package to have our program appear on the robot controller.
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.eventloop.opmode.OpMode;
These lines import the class we are going to extend, OpMode, and the annotation we are going to apply above it, @TeleOp, from the parent package "opmode".
We do not have to generate these import statements ourselves. When we create the next two lines, Studio will ask us if we want it to generate the import lines for us. Press Alt+Enter to accept its help.
@TeleOp(name="", group="")
This is where the first import statement above becomes important. Notice that this line does not end with a semicolon. This is not a normal line of code. Rather, it is a directive to the compiler, telling it to handle this class in a special way (in this case, to add it to the registry of user-accessible TeleOps). Both fields are optional. If the name is omitted, the name of the class is used.
@TeleOp creates a TeleOp, while @Autonomous creates an autonomous OpMode. You can also add @Disabled below this to prevent the OpMode from being accessible on the Driver Station.
public class BoilerPlate_OpMode extends OpMode {
The name of the class must exactly match the name of the file you created (case-sensitive!) to not generate a build error. We are creating the class which contains our OpMode, and it extends the OpMode class in the SDK so we can use or override its functions.
//Put your early stage initialization code here
This is the place to initialize all the variables you will use, notably references to hardware devices.
@Override
public void init() {
We are overriding a method (a.k.a. function) contained within the OpMode class. Using init() as an example, when you click the Init button to start an OpMode, the robot controller calls the init() method. By default, init() is empty, so we need to override it to tell the robot controller that the method actually contains this code instead.
This method is required.init() is called once when the Init button is pressed on the Driver Station.
This is the place to get your hardware devices from the hardwareMap calls and set any of their options that you need, such as motor directions. (If you're not familiar with object-oriented programming, it looks like you're storing a hardware device, which is an object, in a variable, but really you're storing a reference to it. When later code looks at that variable, the variable tells it where the device it wants to interact with is located.)
@Override
public void init_loop() {
This method is optional.
init_loop() is called repeatedly when the Init button is pressed until the Start button is pressed or the OpMode is otherwise aborted.
@Override
public void start() {
This method is optional.
start() is called once when the Start button is pressed.
@Override
public void loop() {
This method is required.
loop() is called repeatedly when the Start button is pressed until the Stop button is pressed or the OpMode is otherwise aborted.
@Override
public void stop() {
This method is optional.
stop() is called once when the Stop button is pressed.
If you need to clean anything up when the OpMode is stopped, do it here.
Follow the comments in the example above (also downloadable as a boilerplate template) to determine where to place the various sections of your code.