> For the complete documentation index, see [llms.txt](https://docs.cb21829.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.cb21829.org/ftc-java-beginner-guide/java-principles-you-actually-need-for-ftc-oop.md).

# Java principles you actually need for FTC (OOP)

You do not need all of Java. You need the OOP pieces the FTC SDK uses.

### Variables and types

```java
int ticks = 1120;
double power = 0.75;
boolean isPressed = true;
String motorName = "frontLeft";
```

Use `double` for motor powers and most robot math. Use `int` for encoder counts.

### Classes and objects

A **class** is a blueprint. An **object** is an instance of that blueprint.

```java
DcMotor frontLeft;
```

`DcMotor` is a class from the SDK. `frontLeft` is a variable that will point to a real motor object.

Your OpMode is also a class:

```java
public class MyFirstTeleOp extends LinearOpMode {
    // your code
}
```

### Inheritance with `extends`

`extends LinearOpMode` means your class inherits SDK behavior. That gives you `hardwareMap`, `telemetry`, `gamepad1`, `waitForStart()`, and `opModeIsActive()`.

### Methods

A **method** is a named block of code.

```java
public double average(double a, double b) {
    return (a + b) / 2.0;
}
```

Common SDK methods:

* `motor.setPower(0.5)`
* `motor.getCurrentPosition()`
* `imu.resetYaw()`

### Fields

Fields are variables declared at the class level.

```java
public class MyFirstTeleOp extends LinearOpMode {
    private DcMotor frontLeft;
    private DcMotor frontRight;

    @Override
    public void runOpMode() {
        frontLeft = hardwareMap.get(DcMotor.class, "frontLeft");
    }
}
```

Use fields for hardware objects you need across the class.

### Access modifiers

* `public` — accessible from anywhere.
* `private` — accessible only inside the class.

Default fields to `private` unless you need something else.

### Annotations

Annotations start with `@`.

```java
@TeleOp(name = "My First TeleOp", group = "Practice")
public class MyFirstTeleOp extends LinearOpMode { ... }
```

`@TeleOp` and `@Autonomous` make the OpMode appear on the Driver Station. `@Override` marks a method you are replacing from a parent class.

### Control flow

```java
if (gamepad1.a) {
    intake.setPower(1.0);
} else {
    intake.setPower(0.0);
}

while (opModeIsActive()) {
    // repeats until the OpMode stops
}
```

That is enough OOP to write solid FTC code.


---

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