In this article, we will mainly look at the function called interface using robots.
An interface is like a class that defines ** method specifications only **. The methods are listed in the interface, but their ** processing ** is not written.
So when you look at a method, you know ** what it does **, but ** what it actually does **. You can see what the method does by looking inside the ** class that implements the interface **.
Point: ** Interface ** Define only the method specifications (return value, method name, arguments) Does not actually process
Point: ** Class that implements the interface ** Define the processing content of the method Actually process
[Reference article] Implemented interface! How to use implements in Java
First, let's take a look at the code below. It is a program that displays characters at the start and end of motor rotation.
MotorEvent.java
import lejos.hardware.motor.EV3LargeRegulatedMotor;
import lejos.hardware.port.MotorPort;
import lejos.robotics.RegulatedMotor;
import lejos.robotics.RegulatedMotorListener;
import lejos.utility.Delay;
public class MotorEvent{
//Instance generation
//RegulatedMotor:interface
//EV3LargeRegulatedMotor:Class that implements the interface
private static RegulatedMotor l_a = new EV3LargeRegulatedMotor(MotorPort.A);
public static void main(String[] args) {
//Instance generation
//Customize the methods in the interface RegulatedMotorListener to define the process
final RegulatedMotorListener listener = new RegulatedMotorListener() {
//Customize the following two methods of the interface RegulatedMotorListener
//Customize the method that is called when the motor starts spinning
@Override
public void rotationStarted(
final RegulatedMotor motor,
final int tachoCount,
final boolean stalled,
final long timeStamp) {
//What to customize
System.out.println("Started");
Delay.msDelay(500);
}
//Customize the method that is called when the motor stops spinning
@Override
public void rotationStopped(
final RegulatedMotor motor,
final int tachoCount,
final boolean stalled,
final long timeStamp) {
//What to customize
System.out.println("Stopped");
Delay.msDelay(500);
}
};
//The addListener method takes an instance of RegulatedMotorListener as an argument
//If there is any movement in the motor, it will be notified to the listener
//And the method in listener is called
l_a.addListener(listener);
l_a.forward();
Delay.msDelay(2000);
l_a.stop();
Delay.msDelay(500);
}
}
I want to use the ** addlistener method ** to display characters at the start and end of motor rotation **. ※void addListener（RegulatedMotorListener listener） Add a listener object that will notify you when rotation starts or stops
Since the addlistener method is implemented in the class EV3LargeRegulatedMotor, ** create a reference type variable l_a from it and use it in the form of l_a.addlistener **.
Also, since the addlistener method takes an instance of ** interface RegulatedMotorListener ** as an argument, it is necessary to first create an instance from that ** interface **.
However, since the interface ** does not define the processing of the method **, even if an instance is created, ** the processing cannot actually be performed **. Therefore, ** customize the method in the interface to define the process ** so that the process can be performed.
◯ Interface: ** Regulated Motor ** Implementation class: EV3LargeRegulatedMotor
◯ Interface: ** RegulatedMotorListener ** Implementation class: None (implemented in the interface)
◯ Method: ** rotationStarted () ** Only specifications are defined in RegulatedMotorListener Method called when the motor starts rotating
◯ Method: ** rotationStopped () ** Only specifications are defined in RegulatedMotorListener Method called at the end of motor rotation
◯ Method: ** addlistener () ** void addListener(RegulatedMotorListener listener) It takes an object ** generated from the interface ** as an argument. Specifications are defined in the interface RegulatedMotor and implemented in the EV3LargeRegulatedMotor class.
◯ Create a class called RotateStateEvent by yourself to implement the interface RegulatedMotorListener. In it, customize the method in RegulatedMotorListener to define the process.
MotorEvent02.java
import lejos.hardware.motor.EV3LargeRegulatedMotor;
import lejos.hardware.port.MotorPort;
import lejos.robotics.RegulatedMotor;
import lejos.robotics.RegulatedMotorListener;
public class MotorEvent02 {
private static RegulatedMotor l_a = new EV3LargeRegulatedMotor(MotorPort.A);
public static void main(String[] args) {
//Take an instance of class RotateStateEvent as an argument
l_a.addListener(new RotateStateEvent());
l_a.forward();
Delay.msDelay(2000);
l_a.stop();
Delay.msDelay(500);
}
}
//Create a class that implements the interface RegulatedMotorListener
class RotateStateEvent implements RegulatedMotorListener{
@Override
public void rotationStarted(
final RegulatedMotor motor,
final int tachoCount,
final boolean stalled,
final long timeStamp) {
//Define the process
System.out.println("Started");
Delay.msDelay(500);
}
@Override
public void rotationStopped(
final RegulatedMotor motor,
final int tachoCount,
final boolean stalled,
final long timeStamp) {
//Define the process
System.out.println("Stopped");
Delay.msDelay(500);
}
}
Point : implements
It can be defined as a class that implements the interface in the form of class implements interface {}.
◯ Create your own SecondCounter class to handle the Timer class. The Timer class takes an instance of the TimerListener interface (the class that implements it) as an argument. Then, ** call the ** timedOut method (= processing) in the TimerListener interface (the class that implements it) ** every specified cycle **.
This time, the program counts the count every 1 second, displays it, and makes a sound every 5 seconds.
import lejos.utility.Timer;
import lejos.hardware.Sound;
import lejos.utility.TimerListener;
public class SecondCounter {
private int second;
//Generate an interrupt every 1000 milliseconds
private Timer timer = new Timer(1000, new CountTimer());
public void reset() {
second = 0;
}
public int getSecond() {
return second;
}
public void start() {
timer.start();
}
public void stop() {
timer.stop();
}
//Create a CountTimer class that implements the interface TimerListener
class CountTimer implements TimerListener {
//TimedOut every 1000ms()The method is called by the Timer
//Customize and define the processing contents of the methods in the interface
@Override
public void timedOut() {
//Add one by one
second++;
System.out.print(second);
//Make a sound every 5 seconds
if(second % 5 == 0 ) {
Sound.beep();
}
}
}
}
import lejos.hardware.Button;
import lejos.hardware.motor.EV3LargeRegulatedMotor;
import lejos.hardware.port.MotorPort;
import lejos.robotics.RegulatedMotor;
import lejos.utility.Delay;
public class SecondCounterSample {
private static RegulatedMotor l_a = new EV3LargeRegulatedMotor(MotorPort.A);
public static void main(String[] args) {
////Creating an instance of the class SecondCounter defined above
SecondCounter counter = new SecondCounter();
//Start counting
counter.start();
//Repeat processing 20 times
for (int i = 0; i < 20; i++) {
if(i == 10) {
//Reset timer
System.out.print("reset ");
counter.reset();
}else if(i > 15) {
//Slow driving
System.out.print("slowdown ");
l_a.setSpeed(100);
}else {
//To accelerate
//count*Set speed to 100
l_a.setSpeed(counter.getSecond() * 100);
}
l_a.forward();
Delay.msDelay(1000);
}
l_a.stop();
counter.stop();
System.out.println("push any button");
Button.waitForAnyPress();
}
}
Point : public Timer(int theDelay,TimerListener el) It takes an instance of the period and TimerListener class (the class that implements it) as arguments.
Point : void timedOut() Called every time the Timer fires. Called every time the Timer fires
Let's look at the relationship between the motor class and the interface.
・ ** Class BaseRegulatedMotor ** ・ ** Class EV3 Large Regulated Motor ** ・ ** Interface Regulated Motor ** ・ ** Interface BaseMotor **
The largest set of motors is the class BaseRegulatedMotor, which EV3LargeRegulatedMotor inherits. The interface RegulatedMotor is implemented in these two classes. It also inherits the interface BaseMotor.
◯ The following interface is implemented BaseMotor,RegulatedMotor...
◯ Subclass EV3LargeRegulatedMotor, EV3MediumRegulatedMotor...
BaseRegulatedMotor.java
//Excerpt from the BaseRegulatedMotor class
public abstract class BaseRegulatedMotor extends Device implements RegulatedMotor{
public void forward()
{
reg.newMove(speed, acceleration, +NO_LIMIT, true, false);
}
public void rotate(int angle, boolean immediateReturn)
{
rotateTo(Math.round(reg.getPosition()) + angle, immediateReturn);
}
public void addListener(RegulatedMotorListener listener)
{
reg.addListener(this, listener);
}
public RegulatedMotorListener removeListener()
{
return reg.removeListener();
}
...
}
Point: ** Inheritance ** You can use extends to inherit a class.
[Reference article] extends keyword
Point : implements
It can be defined as a class that implements the interface in the form of class implements interface {}.
◯ The following interface is implemented Interface: BaseMotor, Encoder, RegulatedMotor, Tachometer
EV3LargeRegulatedMotor.java
//EV3LargeRegulatedMotor class that inherits from BaseRegulatedMotor class
public class EV3LargeRegulatedMotor extends BaseRegulatedMotor
{
public EV3LargeRegulatedMotor(Port port)
{
super(port, null, EV3SensorConstants.TYPE_NEWTACHO, MOVE_P, MOVE_I, MOVE_D,
HOLD_P, HOLD_I, HOLD_D, OFFSET, MAX_SPEED);
}
...
}
◯ Implemented in the following classes BaseRegulatedMotor, EV3LargeRegulatedMotor, EV3MediumRegulatedMotor...
◯ Inherits the interface BaseMotor
//Excerpt from the interface Regulated Motor
public interface RegulatedMotor extends BaseMotor, Tachometer, Closeable {
public void addListener(RegulatedMotorListener listener);
public RegulatedMotorListener removeListener();
void rotate(int angle, boolean immediateReturn);
public void stop(boolean immediateReturn);
...
◯ Interface Interface inherited from Regulated Motor
BaseMotor.java
public interface BaseMotor {
void forward();
void backward();
void stop();
}
Thank you for reading. I would appreciate it if you could let me know if there are any mistakes or points that need to be improved.
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