求指导： Exception in thread "Thread-2" java.lang.NullPointerException

[Elehum]

JAVA新人求指导：
我想用JSlider取值并通过串口将所获得的值发送出去。但目前遇到的问题是Exception in thread "Thread-2" java.lang.NullPointerException
at msproject.Connection.run(Connection.java:49)
at java.lang.Thread.run(Unknown Source)
这个问题不知道应该如何解决。求解答，谢谢！
代码如下：
Connection.java实现通信连接，并使用Thread发送获取数值。

import javax.comm.CommPortIdentifier;
import javax.comm.NoSuchPortException;
import javax.comm.PortInUseException;
import javax.comm.SerialPort;
import javax.comm.UnsupportedCommOperationException;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class Connection implements Runnable{
	/**
	 * 实现通信
	 */
	Test gui;
	Value value;
	CommPortIdentifier portName;
	InputStream input;
	OutputStream output;
	SerialPort serialPort;
	String str = "";
	
	// string format "c+hue+s+sat+l+light+e"
	//String dataForm = "c";
	
	Connection(Test gui) throws NoSuchPortException, PortInUseException, UnsupportedCommOperationException{
		this.gui = gui;
		//this.value = value;
		portName = CommPortIdentifier.getPortIdentifier("COM4");
		serialPort = (SerialPort)portName.open("COMM", 100);
		serialPort.setSerialPortParams(115200, 8, 1, 0);
		
	}
	
	// write data to the output stream
	void Tx_string(String str) throws IOException{
		for(int i=0; i<str.length();i++){
			output.write((int)str.charAt(i));
		}
	}
	
	@Override
	public void run(){
		while(true){
			try{
				
				input = new BufferedInputStream(serialPort.getInputStream());
				output = serialPort.getOutputStream();
				
				output.write(123); // handshake
				
				Tx_string(value.formedData(value.getHue(), value.getSat(), value.getLight()));
				
				
			}catch(IOException e){
				e.printStackTrace();
			}
		}
		
	}
}

Test.java实现GUI。里面使用了三个slider获取数值。

import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.*;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

import javax.comm.NoSuchPortException;
import javax.comm.PortInUseException;
import javax.comm.UnsupportedCommOperationException;

public class Test extends JFrame{
	/**
	 * This class is used for build GUI
	 */
	private static final long serialVersionUID = 1L;
	static Test gui;
	Value val;
	HSLValue hsl = new HSLValue();
	
	JButton start;
	JPanel sPanel;
	
	public Test(){
		
		this.setTitle("GUI");
		this.setLayout(new BorderLayout());
		//this.setLocationRelativeTo(null);
		this.addWindowListener(new WindowAdapter(){
			@Override
			public void windowClosing(WindowEvent e){
				super.windowClosing(e);
				System.exit(0);
			}
		});
		/**
		 * start.addActionListener()实现点击按钮启动thread。 
		 */
		start = new JButton("START");
		start.addActionListener(new ActionListener(){
			@Override
			public void actionPerformed(ActionEvent e){
				Connection co;
				try{
					co = new Connection(gui);
					Thread thread_com = new Thread(co);
					thread_com.start();
				}catch(NoSuchPortException e1){
					e1.printStackTrace();
				}catch(PortInUseException e1){
					e1.printStackTrace();
				}catch(UnsupportedCommOperationException e1){
					e1.printStackTrace();
				}
			}
		});
		
		sPanel = new JPanel();
		sPanel.setLayout(new FlowLayout());
		sPanel.add(start);
		
		this.add(sPanel, BorderLayout.NORTH);
		this.add(hsl, BorderLayout.CENTER);
		this.setDefaultCloseOperation(EXIT_ON_CLOSE);
		this.setSize(500, 600);
		this.setVisible(true);
		
	}
	
	public static void main(String arg[]){
		new Test().setVisible(true);
		
	}
}

class HSLValue extends JPanel{
	/**
	 * create a slider panel.
	 */
	private static final long serialVersionUID = 1L;
	Value val = new Value();
	JSlider hueSlider, satSlider, lightSlider;
	
	JLabel hueLabel = new JLabel("HUE SLIDER");
	JLabel satLabel = new JLabel("SATURATION SLIDER");
	JLabel lightLabel = new JLabel("LIGHT SLIDER");
	JLabel hueValue = new JLabel("");
	JLabel satValue = new JLabel("");
	JLabel lightValue = new JLabel("");
	
	JPanel sliderPanel;
	
	public HSLValue(){
		
		hueSlider = new JSlider(JSlider.HORIZONTAL, 0, 360, 0);
		hueSlider.addChangeListener(new SliderListener());
		satSlider = new JSlider(JSlider.HORIZONTAL, 0, 100, 0);
		satSlider.addChangeListener(new SliderListener());
		lightSlider = new JSlider(JSlider.HORIZONTAL, 0, 100, 0);
		lightSlider.addChangeListener(new SliderListener());
		
		sliderPanel = new JPanel();
		sliderPanel.setLayout(new GridLayout(9, 1, 30, 0));
		sliderPanel.setSize(500,500);
		
		
		
		sliderPanel.add(hueLabel);
		sliderPanel.add(hueSlider);
		sliderPanel.add(hueValue);
		sliderPanel.add(satLabel);
		sliderPanel.add(satSlider);
		sliderPanel.add(satValue);
		sliderPanel.add(lightLabel);
		sliderPanel.add(lightSlider);
		sliderPanel.add(lightValue);
		
		this.add(sliderPanel);
		this.setVisible(true);
	}
	
	class SliderListener implements ChangeListener{
		public void stateChanged(ChangeEvent e){
			JSlider slider = (JSlider)e.getSource();
			
			if(slider == hueSlider){
				hueValue.setText("Selected Hue : " + slider.getValue()); //GUI 显示数值
				val.setHue(slider.getValue());
				
			}else if(slider == satSlider){
				
				val.setSat(slider.getValue());
				satValue.setText("Selected Saturation : " + val.getSat());
			}else if(slider == lightSlider){
				lightValue.setText("Selected Light : " + slider.getValue());
				val.setLight(slider.getValue());
			}
			
		}
	}
	
}

Value.java 我只是想通过这个类方便其他两个类传递数值。

public class Value {
	/**
	 * this class is used for get HSL values.
	 */
	int hue = 0;
	int sat = 0;
	int light = 0;
	String dataForm = "";
	
	public int getHue(){
		return hue;
	}
	public void setHue(int hue){
		this.hue = hue;
	}
	
	public int getSat(){
		return sat;
	}
	public void setSat(int sat){
		this.sat = sat;
	}
	
	public int getLight(){
		return light;
	}
	public void setLight(int light){
		this.light = light;
	}
	
	/*public String toString(int i){
		return i+"";
	}*/
	// build output data format.
	public String formedData(int hue, int sat, int light){
		String dataForm = "c";
		dataForm += hue;
		dataForm += "s";
		dataForm += sat;
		dataForm += "l";
		dataForm += light;
		dataForm += "e";
		System.out.println(dataForm);
		
		return dataForm; // c+hue+s+sat+l+light+e
	}
}

[三仙半]

看你的代码，第49行是

output = serialPort.getOutputStream();

错误提示是空指针，我分析，是不是serialPort获取失败啊？你debug一下看看

[Elehum]

不应该是serial port 的问题吧， 因为如果再开一个GUI启动串口会报错： PortInUse。 说明已经与COM4连接了。

[三仙半]

哦，是啊，如果serialPort 是null了，那么第二句代码就过不去了。

serialPort = (SerialPort)portName.open("COMM", 100);
serialPort.setSerialPortParams(115200, 8, 1, 0);

我再看看啊，怎么会空指针了呢。我机器没串口，调试不了，愁人。

[三仙半]

我看到的49行是提示中指的那个49行吧？

[Elehum]

麻烦你了。我刚接触线程，好多都不是很懂

[三仙半]

我QQ是597882752，有兴趣可以加一下，聊着方便