Template:Language - Java Write Code

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By following the instructions for your operating system and compiler above, you now have working examples and a project that is configured. This teaching section will help you understand how the examples were written so you can start writing your own code.


Remember: your main reference for writing Java code will be the Phidget22 API Manual and the example code.

Step One: Create and Address

You will need to create your Phidget object in your code. For example, we can create a digital input object like this:

DigitalInput ch = new DigitalInput();

Next, we can address which Phidget we want to connect to by setting parameters such as DeviceSerialNumber.

ch.setDeviceSerialNumber(496911);

Although we are not including it on this page, you should handle the return codes of all Phidget functions. Here is an example of the previous code with error handling:

try {
    DigitalInput ch = new DigitalInput();
    ch.setDeviceSerialNumber(496911);
} catch (PhidgetException ex) {
    System.out.println(ex.getDescription());
}

Step Two: Open and Wait for Attachment

After we have specified which Phidget to connect to, we can open the Phidget object like this:

ch.open(5000);

To use a Phidget, it must be plugged in (attached). We can handle this by calling open(timeout), which will block indefinitely until a connection is made, or until the timeout value is exceeded. Simply calling open() does not guarantee you can use the Phidget immediately.

Alternately, you could verify the device is attached by using event driven programming and tracking the attach events.

To use events to handle attachments, we have to modify our code slightly:

ch.addAttachListener(new AttachListener() {
    public void onAttach(AttachEvent ae) {
        printf("Phidget attached!\n");
});

ch.open(5000);

We recommend using this attach listener to set any initialization parameters for the channel such as DataInterval and ChangeTrigger from within the AttachListener, so the parameters are set as soon as the device becomes available.

Step Three: Do Things with the Phidget

We recommend the use of event driven programming when working with Phidgets. In a similar way to handling an attach event as described above, we can also add an event listener for a state change event:

DigitalInput ch = new DigitalInput();

ch.addAttachListener(new AttachListener() {
    public void onAttach(AttachEvent ae) {
        printf("Phidget attached!\n");
});

ch.addStateChangeListener(new DigitalInputStateChangeListener() {
    public void onStateChange(DigitalInputStateChangeEvent e) {
        System.out.println("State changed: " + e.getState());
    }
});

ch.open(5000);

This code will connect a function to an event. In this case, the onStateChange function will be called when there has been a change to the channel's input.

If you are using multiple Phidgets in your program, check out our page on Using Multiple Phidgets for information on how to properly address them and use them in events.

If events do not suit your needs, you can also poll the device directly for data using code like this:

boolean state = ch.getState();
System.out.println("State: " + state);

Important Note: There will be a period of time between the attachment of a Phidget sensor and the availability of the first data from the device. Any attempts to get this data before it is ready will result in an exception. See more information on this on our page for Unknown Values.

Enumerations

Some Phidget devices have functions that deal with specific predefined values called enumerations. Enumerations commonly provide readable names to a set of numbered options.

Enumerations with Phidgets in Java will take the form of com.phidget22.EnumerationType.ENUMERATION_NAME.

For example, specifying a SensorType to use the 1142 for a voltage input would look like:

com.phidget22.VoltageSensorType.PN_1142

and specifying a K-Type thermocouple for a temperature sensor would be:

com.phidget22.ThermocoupleType.K

The Phidget error code for timing out could be specified as:

com.phidget22.ErrorCode.TIMEOUT

You can find the Enumeration Type under the Enumerations section of the Phidget22 API for your device, and the Enumeration Name in the drop-down list within.

Step Four: Close and Delete

At the end of your program, be sure to close your device:

ch.close();