我需要一些帮助将python代码转换为java。我是Python的新手，我不知道所有的功能/方法/等。我使用这个Python代码从Raspberry Pi上的2个传感器读取一些数据，我需要用Java获取这些数据。
这是Python代码：
#!/usr/bin/python
import spidev
import time
import os
# Open SPI bus
spi = spidev.SpiDev()
spi.open(0,0)
# Function to read SPI data from MCP3008 chip
# Channel must be an integer 0-7
def ReadChannel(channel):
adc = spi.xfer2([1,(8+channel)<<4,0])
data = ((adc[1]&3) << 8) + adc[2]
return data
# Function to convert data to voltage level,
# rounded to specified number of decimal places.
def ConvertVolts(data,places):
volts = (data * 3.3) / float(1023)
volts = round(volts,places)
return volts
# Function to calculate temperature from
# TMP36 data, rounded to specified
# number of decimal places.
def ConvertTemp(data,places):
# ADC Value
# (approx) Temp Volts
# 0 -50 0.00
# 78 -25 0.25
# 155 0 0.50
# 233 25 0.75
# 310 50 1.00
# 465 100 1.50
# 775 200 2.50
# 1023 280 3.30
temp = ((data * 330)/float(1023))-50
temp = round(temp,places)
return temp
# Define sensor channels
light_channel = 0
temp_channel = 1
# Define delay between readings
delay = 5
while True:
# Read the light sensor data
light_level = ReadChannel(light_channel)
light_volts = ConvertVolts(light_level,2)
# Read the temperature sensor data
temp_level = ReadChannel(temp_channel)
temp_volts = ConvertVolts(temp_level,2)
temp = ConvertTemp(temp_level,2)
# Print out results
print "--------------------------------------------"
print("Light: {} ({}V)".format(light_level,light_volts))
print("Temp : {} ({}V) {} deg C".format(temp_level,temp_volts,temp))
# Wait before repeating loop
time.sleep(delay)
这是我尝试过的Java代码（我使用的是Pi4j库）：
import com.pi4j.io.gpio.GpioController;
import com.pi4j.io.gpio.GpioFactory;
import com.pi4j.io.gpio.GpioPinDigitalInput;
import com.pi4j.io.gpio.GpioPinDigitalOutput;
import com.pi4j.io.gpio.Pin;
import com.pi4j.io.gpio.RaspiPin;
public class MCP3008_TMP36 {
private static Pin spiClk = RaspiPin.GPIO_01; // Pin #18, clock
private static Pin spiMiso = RaspiPin.GPIO_04; // Pin #23, data in. MISO: Master In Slave Out
private static Pin spiMosi = RaspiPin.GPIO_05; // Pin #24, data out. MOSI: Master Out Slave In
private static Pin spiCs = RaspiPin.GPIO_06; // Pin #25, Chip Select
private enum MCP3008_channels {
CH0(0), CH1(1), CH2(2), CH3(3), CH4(4), CH5(5), CH6(6), CH7(7);
private int ch;
MCP3008_channels(int chNum) {
this.ch = chNum;
}
public int ch() {
return this.ch;
}
}
private static GpioPinDigitalInput misoInput = null;
private static GpioPinDigitalOutput mosiOutput = null;
private static GpioPinDigitalOutput clockOutput = null;
private static GpioPinDigitalOutput chipSelectOutput = null;
private static boolean run = true;
public static void main(String[] args){
GpioController gpio = GpioFactory.getInstance();
//TODO
while(run){
float lightLevel = channelReading(MCP3008_channels.CH0);
float lightVolts = convertVolts(lightLevel);
float tempLevel = channelReading(MCP3008_channels.CH1);
float tempVolts = convertVolts(tempLevel);
float temp = convertTemp(tempVolts);
System.out.println("Light: " + lightLevel+"/"+lightVolts+"V");
System.out.println("Temp:"+temp+"/"+tempVolts+"V");
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("Bye...");
gpio.shutdown();
}
public static float convertVolts(float data){
//TODO
float rez = (float) ((data * 3.3)/1023);
float rez1 = Math.round(rez);
return rez1;
}
public static float convertTemp(float data){
//TODO
float rez = (float) ((data * 330)/1023)-50;
float rez1 = Math.round(rez);
return rez1;
}
private static int channelReading(MCP3008_channels channel) {
chipSelectOutput.high();
clockOutput.low();
chipSelectOutput.low();
int adccommand = channel.ch();
adccommand |= 0x18; // 0x18: 00011000
adccommand <<= 3;
// Send 5 bits: 8 - 3. 8 input channels on the MCP3008.
for (int i = 0; i < 5; i++) //
{
if ((adccommand & 0x80) != 0x0) // 0x80 = 0&10000000
mosiOutput.high();
else
mosiOutput.low();
adccommand <<= 1;
clockOutput.high();
clockOutput.low();
}
int adcOut = 0;
for (int i = 0; i < 12; i++) // Read in one empty bit, one null bit and
// 10 ADC bits
{
clockOutput.high();
clockOutput.low();
adcOut <<= 1;
if (misoInput.isHigh()) {
// System.out.println(" " + misoInput.getName() +
// " is high (i:" + i + ")");
// Shift one bit on the adcOut
adcOut |= 0x1;
}
}
chipSelectOutput.high();
adcOut >>= 1; // Drop first bit
return adcOut;
}
}
我想知道这个java代码是否正常还是需要修改。
这是我开始运行的结果：
Exception in thread "main" java.lang.NullPointerException
at MCP3008_TMP36.channelReading(MCP3008_TMP36.java:80)
at MCP3008_TMP36.main(MCP3008_TMP36.java:44)
我不确定＆＃34; channelReading＆＃34;功能还可以。请帮帮我。
非常感谢！
答案 0 :(得分：1)
这是你的java代码的一个问题，与Python（还）无关。
看看你得到的错误，
Exception in thread "main" java.lang.NullPointerException
at MCP3008_TMP36.channelReading(MCP3008_TMP36.java:80)
at MCP3008_TMP36.main(MCP3008_TMP36.java:44)
您应该查看代码中的第80行，即
chipSelectOutput.high();
private static int channelReading(MCP3008_channels channel) {
从主方法的第44行调用
float lightLevel = channelReading(MCP3008_channels.CH0);
所以你要调用方法chipSelectOutput.high()，但是看看你的其余代码，我们有
private static GpioPinDigitalOutput chipSelectOutput = null;
并且您从未创建/为此变量分配对象，因此当您从中调用方法时，chipSelectOutput仍具有值null。这就是你得到NullPointerException的原因。
在执行任何其他操作之前，您需要在代码中的某处创建chipSelectOutput对象，以便有一个对象来调用该函数。
以下是如何/应该初始化静态成员的示例：
static variable initialization java
private static final B a = new B(); // consider making it final too
如果此方法有效，那么出于同样的原因，对于您尚未初始化的其他对象clockOutput，mosiOutput和misoInput，您将收到相同类型的错误（在任何地方给出一个值。