我正在通过串口尝试使用Arduino的Java JFrame，我遇到了问题，我不知道如何继续使用我的代码。
我试图使用构造函数从另一个类中的JFrame代码调用一个类的串行端口部分。基本上，我正在尝试将我的Java程序与Arduino Uno连接。
我的问题是，当我尝试从GUI类运行代码时，在 SerialOut.write（＆＃34; test＆＃34; .getBytes（））; ，错误说＆＃34;线程中出现例外＆＃34; main＆＃34; java.lang.NullPointerException＆＃34;。
有人可以看看构造函数并告诉我是否犯了错误吗？谢谢！
用于设置串行端口的类此代码本身可以工作[我使用Uno和LED测试它以查看它是否亮起。 （确实如此）]
package javaapplication1;
import javaapplication1.RCDA_JFrame;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStream;
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import gnu.io.SerialPortEvent;
import gnu.io.SerialPortEventListener;
import java.util.Enumeration;
import java.io.IOException;
public class SerialTest implements SerialPortEventListener {
//constructor
public SerialTest(){
this.initialize();
this.close();
this.serialEvent(null);
}
SerialPort serialPort;
/** The port we're normally going to use. */
private static final String PORT_NAMES[] = {
"COM8",}; // Windows
private BufferedReader input;
private static OutputStream SerialOut;/** The output stream to the port */
private static final int TIME_OUT = 2000;/** Milliseconds to block while waiting for port open */
private static final int DATA_RATE = 9600;/** Default bits per second for COM port. */
public void initialize() {
CommPortIdentifier portId = null;
Enumeration portEnum = CommPortIdentifier.getPortIdentifiers();
//First, Find an instance of serial port as set in PORT_NAMES.
while (portEnum.hasMoreElements()) {
CommPortIdentifier currPortId = (CommPortIdentifier) portEnum.nextElement();
for (String portName : PORT_NAMES) {
if (currPortId.getName().equals(portName)) {
portId = currPortId;
break;
}
}
}
if (portId == null) {
System.out.println("Could not find COM port.");
return;
}
try {
// open serial port, and use class name for the appName.
serialPort = (SerialPort) portId.open(this.getClass().getName(),
TIME_OUT);
// set port parameters
serialPort.setSerialPortParams(DATA_RATE,
SerialPort.DATABITS_8,
SerialPort.STOPBITS_1,
SerialPort.PARITY_NONE);
// open the streams
input = new BufferedReader(new InputStreamReader(serialPort.getInputStream()));
SerialOut = serialPort.getOutputStream();
// add event listeners
serialPort.addEventListener(this);
serialPort.notifyOnDataAvailable(true);
} catch (Exception e) {
System.err.println(e.toString());
}
}
/**
* This should be called when you stop using the port.
* This will prevent port locking on platforms like Linux.
*/
public synchronized void close() {
if (serialPort != null) {
serialPort.removeEventListener();
serialPort.close();
}
}
//Handle an event on the serial port. Read the data and print it.
public synchronized void serialEvent(SerialPortEvent oEvent) {
if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE) {
try {
String inputLine=input.readLine();
System.out.println(inputLine);
} catch (Exception e) {
System.err.println(e.toString());
}
}
}
public static void main(String[] args) throws Exception {
SerialTest main = new SerialTest();
main.initialize();
Thread t=new Thread() {
public void run() {
//the following line will keep this app alive for 1000 seconds,
//waiting for events to occur and responding to them (printing incoming messages to console).
try {Thread.sleep(1000000);} catch (InterruptedException ie) {}
}
};
t.start();
System.out.println("Started");
//testing
try {
System.out.println("This is a test");
System.out.println("test".getBytes());
SerialOut.write("test".getBytes()); //SEND STRING THROUGH SERIAL PORT
} catch (IOException e1) {
e1.printStackTrace();
} //end of testing
}
}
JFrame类 - 我试图调用上面的类：
package javaapplication1;
import javaapplication1.SerialTest;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStream;
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import gnu.io.SerialPortEvent;
import gnu.io.SerialPortEventListener;
import java.util.Enumeration;
import java.io.IOException;
public class NewJFrame extends javax.swing.JFrame implements SerialPortEventListener {
@Override
public void serialEvent(SerialPortEvent ev) {
SerialTest ST1 = new SerialTest();
}
private static OutputStream SerialOut;
SerialPort serialPort;
/** The port we're normally going to use. */
// private static final String PORT_NAMES[] = {
// "COM8"}; // Windows
// private BufferedReader input;
// private static final int TIME_OUT = 2000;/** Milliseconds to block while waiting for port open */
// private static final int DATA_RATE = 9600;/** Default bits per second for COM port. */
//
public NewJFrame() {
initComponents();
}
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
}
public static void main(String args[]) {
//constructor from SerialTest
SerialTest ST1 = new SerialTest();
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new NewJFrame().setVisible(true);
}
});
try {
System.out.println("This is a test");
System.out.println("test".getBytes());
SerialOut.write("test".getBytes()); //SEND STRING THROUGH SERIAL PORT
} catch (IOException e1) {
e1.printStackTrace();
}
}
// Variables declaration - do not modify
private javax.swing.JButton jButton1;
// End of variables declaration
}
答案 0 :(得分：1)
在进入可用端口列表后，您有错误检查以查看端口是否为空。确保它确实获得了可用的端口，并确保为其分配了值。
schema要确认尝试打印出portName以查看它实际上正在获得的端口if (portId == null) {
System.out.println("Could not find COM port.");
return;
}
，并检查以确保它不为空。如果是，那就是你的问题。
答案 1 :(得分：0)
private static OutputStream SerialOut;/** The output stream to the port */
这是SerialTest.注意它不应该是静态的。如果发现端口，则在调用initialize()时初始化，并且由于initialize()不会抛出异常或返回任何状态，因此无法知道它是否成功。解决了这个问题。
private static OutputStream SerialOut;
那是NewJFrame。它与前一个数据项不同。它永远不会被初始化，所以它是null，所以你得到一个NullPointerException。将其删除，然后使用SerialTest.