Below is the sample code and the apis;

package demo; import eapi.*;

public class App {

    public static void main(String args[]) {

        final Led led = Led.init('C', 13); // Port C Pin 13
        PushButton pushButton = PushButton.init('A',
                                                8, //Port A Pin 8
                                                GPIO.INPUT_PULL_UP,
                                                GPIO.FALLING_EDGE,
                                                200, //debounce
                                                (time) -> {
            Core.println("push button event");
            led.flip();
        });

        while (true) {
            Looper.loop();
        }

}

Analog.inSetup(Analog.IN1); Analog.read(Analog.IN1);

Analog.outSetup(Analog.OUT5); Analog.write(Analog.OUT5, (short)255);

I2C.setup(I2C.I2C2, 400); SPI.setup(SPI.SPI_ID2, 0, SPI.SPI_MODE_3, SPI.SPI_FB_MSB);

References: https://stm32-base.org/boards/STM32F103C8T6-Blue-Pill.html