java.util.regex.PatternSyntaxException

Question

I have modified the BluetoothChat code to receive serial data from a micro-controller to my android phone. When I run the following code snippet it gives java.util.regex.PatternSyntaxException. What exactly is the error? Why is this exception happening?

BluetoothChat.java

// The Handler that gets information back from the BluetoothChatService
private final Handler mHandler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
        switch (msg.what) {

        case MESSAGE_WRITE:

            byte[] writeBuf = (byte[]) msg.obj;
            // construct a string from the buffer
            String writeMessage = new String(writeBuf);
            mConversationArrayAdapter.add(writeMessage);
            break;

        case MESSAGE_READ:

            byte[] readBuf = (byte[]) msg.obj;       

           // construct a string from the valid bytes in the buffer

            String readMessage = new String(readBuf, 0, msg.arg1);

            if(readMessage.matches("*"))
            {
               mConversationArrayAdapter.add("Left");
            }
            else

            {mConversationArrayAdapter.add(readMessage);}

 }

Log-cat:

      09-15 13:54:32.070: E/AndroidRuntime(21931): FATAL EXCEPTION: main
      09-15 13:54:32.070: E/AndroidRuntime(21931): java.util.regex.PatternSyntaxException: Syntax         error in regexp
 pattern near index 1:
      09-15 13:54:32.070: E/AndroidRuntime(21931): *
      09-15 13:54:32.070: E/AndroidRuntime(21931):  ^
      09-15 13:54:32.070: E/AndroidRuntime(21931):  at java.util.regex.Pattern.compileImpl(Native Method)
      09-15 13:54:32.070: E/AndroidRuntime(21931):  at java.util.regex.Pattern.compile(Pattern.java:400)
      09-15 13:54:32.070: E/AndroidRuntime(21931):  at java.util.regex.Pattern.<init>(Pattern.java:383)
      09-15 13:54:32.070: E/AndroidRuntime(21931):  at java.util.regex.Pattern.matches(Pattern.java:413)
      09-15 13:54:32.070: E/AndroidRuntime(21931):  at java.lang.String.matches(String.java:1765) 09-15 13:54:32.070:
 E/AndroidRuntime(21931):   at
 com.example.footforthought.Sixth$2.handleMessage(Sixth.java:289)
      09-15 13:54:32.070: E/AndroidRuntime(21931):  at android.os.Handler.dispatchMessage(Handler.java:99)
      09-15 13:54:32.070: E/AndroidRuntime(21931):  at android.os.Looper.loop(Looper.java:137)
      09-15 13:54:32.070: E/AndroidRuntime(21931):  at   android.app.ActivityThread.main(ActivityThread.java:4517)
      09-15 13:54:32.070: E/AndroidRuntime(21931):  at java.lang.reflect.Method.invokeNative(Native Method)
      09-15 13:54:32.070: E/AndroidRuntime(21931):  at java.lang.reflect.Method.invoke(Method.java:511)
      09-15 13:54:32.070: E/AndroidRuntime(21931):  at  .android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
      09-15 13:54:32.070: E/AndroidRuntime(21931):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
      09-15 13:54:32.070: E/AndroidRuntime(21931):  at dalvik.system.NativeStart.main(Native Method)

laalto · Accepted Answer · 2014-09-15 08:48:47Z

3

matches() uses regular expressions (regex) for matching the input and * is a regex metacharacter, meaning zero or more of the previous token. Since there's no previous token, it's a syntax error.

If you want to match * literally, escape it with backslash:

readMessage.matches("\\*")

or use some of the string-matching functions such as equals() that don't use a regular expression.

answered Sep 15, 2014 at 8:48

laalto

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1 Comment

user3211607 Over a year ago

Sir, is there any modification to be made if I am reading a two digit number? "mConversationArrayAdapter.add(readMessage);" is giving me a two digit number as two separate digits..

TheLostMind · Accepted Answer · 2014-09-15 08:48:41Z

1

Here is your problem :

if(readMessage.matches("*")

If you want to match everything, then use ".*.

Also, like laalto says in his answer. If you want to match everything, you have to escape * either by using Pattern.quote() or by simply using two slashes "\\*".

answered Sep 15, 2014 at 8:48

TheLostMind

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