Is there any way to retrieve the declaring class of an instance at runtime?
For example:
public class Caller {
private JFrame frame = new JFrame("Test");
private JButton button = new JButton("Test me");
private Callee callee = new Callee();
public Caller() {
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(button);
button.addActionListener(callee.getListener());
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
new Caller();
}
}
The callee:
public class Callee {
public ActionListener getListener() {
return new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
/* Get the class "Caller" here and invoke its methods */
/* Something along the lines of: */
Object button = e.getSource();
button.getOwnerClass(); //This would return the type Caller
}
};
}
}
"getOwnerClass()" is an imaginary method. Is there a way to get a result similar to that?
There is nothing in the standard API that allows you to get this information. It's a bit unclear what you mean with 'declaring class' or 'owner class' but for this sake of this answer I'll assume that it is the class whose code created the instance of the object (that you want the owner class from).
This information is not stored by the JVM by default.
But, using the heap profiler that is packaged along with the JDK distribution, you can record the stacktrace of the point at which objects are allocated, and this information can be written to a file on various points in time.
That still doesn't give you an API call to retrieve the information, but it shows that it is technically possible to record this type of information.
I search a bit on Google and found that someone did create an API that uses the same basic technique as the heap profiler (the java.lang.instrumentation package/JVMTI interface)
Open source project: java-allocation-instrumenter
With a bit of work you should be able to build something with it.
The site has a nice example:
AllocationRecorder.addSampler(new Sampler() {
public void sampleAllocation(int count, String desc, Object newObj, long size) {
System.out.println("I just allocated the object " + newObj +
" of type " + desc + " whose size is " + size);
if (count != -1) { System.out.println("It's an array of size " + count); }
}
});
Instead of printing, you should get the stacktrace using new Exception().getStackTrace(), remove the first few StackTraceElement objects that refer to the sampler and the API classes, and then call StackTraceElement.getClassName() to get the name of the class that created the object instance, in other words, your OwnerClass.
Related
I am trying to extract the calls from the method run() to the constructors. Here is the code I am trying to parse
SwingUtilities.invokeLater(new Runnable() {
public void run() {
// Create the two text areas
TextAreaFigure ta = new TextAreaFigure();
ta.setBounds(new Point2D.Double(10,10),new Point2D.Double(100,100));
TextAreaFigure tb = new TextAreaFigure();
tb.setBounds(new Point2D.Double(210,110),new Point2D.Double(300,200));
// Create an elbow connection
ConnectionFigure cf = new LineConnectionFigure();
cf.setLiner(new ElbowLiner());
// Connect the figures
cf.setStartConnector(ta.findConnector(Geom.center(ta.getBounds()), cf));
cf.setEndConnector(tb.findConnector(Geom.center(tb.getBounds()), cf));
// Add all figures to a drawing
Drawing drawing = new DefaultDrawing();
drawing.add(ta);
drawing.add(tb);
drawing.add(cf);
// Show the drawing
JFrame f = new JFrame("My Drawing");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setSize(400,300);
DrawingView view = new DefaultDrawingView();
view.setDrawing(drawing);
f.getContentPane().add(view.getComponent());
f.setVisible(true);
}
});
}
Here is the code I am using to extract the calls from method run() to the constructors. The problem that I have is that the last line: String constructorClassName= cons.getExecutable().getDeclaringType().toString(); is returning the wrong class name, instead of getting "jhot.draw.TextAreaFigure()" as the name I am getting "jhot.mini.samples.TextAreaFigure()". The file that I am parsing is located under "jhot.mini.samples" while the constructor is declared within "jhot.draw.TextAreaFigure()". I am not sure if this is a bug in spoon or if I am using the wrong API to retrieve the constructor calls.
for(CtMethod<?> method :clazz.getMethods()) {
List<CtConstructorCall> ctNewClasses = method.getElements(new TypeFilter<CtConstructorCall>(CtConstructorCall.class));
for( CtConstructorCall myclass: ctNewClasses) {
//CONSTRUCTOR
if(myclass instanceof CtConstructorCall<?>) {
System.out.println("yes");
List<CtMethod> methoddeclared = myclass.getElements(new TypeFilter<CtMethod>(CtMethod.class));
for(CtMethod<?> meth: methoddeclared) {
methodinside=meth.getSignature();
methodinsideclass=clazz.getQualifiedName();
String mymethod=methodinsideclass+"."+methodinside;
ResultSet methodsinside = st.executeQuery("SELECT methods.* from methods where methods.fullmethod='"+mymethod+"'");
//while(callingmethodsrefined.next()){
if(methodsinside.next()) {
MethodIDINSIDE = methodsinside.getString("id");
CLASSNAMEINSIDE = methodsinside.getString("classname");
CLASSIDINSIDE = methodsinside.getString("classid");
//System.out.println("CALLEE METHOD ID: "+ CALLEEID);
}
List<CtConstructorCall> constructors = meth.getElements(new TypeFilter<CtConstructorCall>(CtConstructorCall.class));
for(CtConstructorCall<?> cons: constructors) {
String constructorClassName= cons.getExecutable().getDeclaringType().toString();
}
}
}
}
I am not sure if this is a bug in spoon or if I am using the wrong API to retrieve the constructor calls.
I'm one of the contributor of Spoon. It looks to me that you're using the right API, but I'm not sure because your example looks a bit messy here.
I think it would be easier if you open an issue on Spoon Github repository and specify:
the project you're working on if it's open-source
how you launch Spoon (the version of Spoon, arguments, etc)
what do you expect exactly
Then we could investigate to check exactly what happens there. Thanks!
What I want to achieve is very simple.
I have 2 classes. "SpeedingTicket" & "SpeedingTicket GUI".
Inside my GUI I have 1 textbox name txtSpeedLimit & a button.
Inside my SpeedingTicket class I have a variable "int speedingTicket".
Inside my SpeedingTicket class I also have a get & set method for "speedingTicket".
I know how to get and set text using JTextFields, but I want to be able to:
receive input from the "txtSpeedLimit", and store that value into the "txtSpeedLimit" instance variable in the "SpeedTicket" class. I can then check for validation etc when I come to adding the vehicle speed.
Maybe this isn't the most efficient way of dealing with this program. Maybe I should scrap the instance variables in SpeedingTicket, and deal with it all in the GUI.
Any advice would be hugely appreciated.
Basically what I'm trying to do is this:
class confirmHandler implements ActionListener{
public void actionPerformed(ActionEvent e){
String val = txtSpeedLimit.getText();
int realNum = speed.getSpeedLimit() = txtSpeedLimit; < but obviously that doesn't work, but I want the textbox link to the variable.
EDIT: If we take away the GUI, all I want my program to do is the following:
Speed Limit: 50 < enterd via textfield
Speed: 60 < entered via textfield
if the speed is blah blah (ive already coded this).. then output a result to one of my labels.
I achieved this without making a GUI and making it only console based, but instead of the user typing it via the console, I want it to be typed via textfields.
THe values that are entered into the textfields should be stored in the two variables (speed and speedlimit) that are in the SpeedingTicket class.
You can update a value in:
public class SpeedingTicket {
int speedingTicket;
public SpeedingTicket() {
speedingTicket = 500;
}
public int getSpeedingTicket() {
return speedingTicket;
}
}
by:
public class SpeedingTicketGUI extends JPanel{
SpeedingTicket st;
SpeedingTicketGUI() {
st = new SpeedingTicket();
setLayout(new FlowLayout(FlowLayout.LEFT));
JTextField txtField = new JTextField(10);
txtField.setText(""+st.getSpeedingTicket());
add(txtField);
JButton btn = new JButton("Update");
btn.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
setSpeedingTicket(txtField.getText());
}
});
add(btn);
}
private void setSpeedingTicket(String text) {
try {
int speedTicket = Integer.parseInt(text);
st.setSpeedingTicket(speedTicket);
System.out.println("Speeding ticket set to " +st.getSpeedingTicket());
} catch (NumberFormatException ex) {
System.out.println("Invalid value " +text);
ex.printStackTrace();
}
}
public static void main(String[] args){
JFrame frame = new JFrame("Speeding Ticket");
frame.setSize(400,100);
frame.add(new SpeedingTicketGUI());
frame.setVisible(true);
}
}
You don't need to store values in JText or any GUI componenets...
Use global static variables. For example:
public static int speed_limit;
You can access this variable from ANY method,class, etc.
There are multiple ways to do it.
You can detect textfield changes by using a DocumentListener or if you want (not recommended) by a KeyListener.
The Listener could be implemented directly by your gui class or by your other class. If you want more abstraction you could implement the DocumentListener by your gui class and create a method
public void addSpeedChangeListener(SpeedChangeListener scl) {
this.speedChangeListeners.add(scl);
}
Your SpeedChangeListener could be very simple:
public interface SpeedChangeListener {
public void speedChanged(int value);
}
Then your second class implements the SpeedChangeListener and calls addSpeedChangeListener(this) on your gui class. Inside the gui class, your document listener calls speedChanged(val) for every listener registered.
EDIT
You can also use the Button and call the speedChanged on every listener inside the actionPerformed method of the ActionListener.
I think it would be easier to use a JOptionDialog which pop ups when the button is clicked. That way you can easily get input and also validate the input straight away.
I am programming an application that deals with orders from a database. It has several pages, a navigation, a header that always should show information about the actual order you are working with and a content area, in which the details of said order get shown:
My MainProgram extends a JFrame and contains a CardLayout, in which the other pages are hosted, so when the user clicks on the page in the navigation, only the view of the content-area changes. Logo, header and the navigation stay the same. The header keeps displaying the order number.
As there are several different pages that contain details about the same order, I need to "send / transfer" information about the order from one page to the other so I can show some information in the header and in the content area from the order object.
But I am not getting this to work as intended, mostly to my misunderstand of static and when to use it, where objects get created exactly and also the complexity of my program: I am using a class that is intended for the navigation and therefore should also handle
the information transfer from one page to the other.
Since I am using a database, creating a MVCE will be hard, so instead I will show the important parts of my program.
MainProgram.java
Here the navigation and the content panel (centerPanel) get created, also the CardLayout. centerPanel and the CardLayout are static, so I can call this from other classes and switch the page that is shown (probably not a good idea?):
NavigationPanel navigationPanel = new NavigationPanel();
public static JPanel centerPanel = new JPanel();
public static CardLayout contentCardsLayout = new CardLayout();
I create the pages and put them into my CardLayout:
OverviewPage overviewPage = new OverviewPage();
BasicDataPage basicDataPage = new BasicDataPage();
centerPanel.setLayout(contentCardsLayout);
overviewPage.setName("overviewPage");
basicDataPage.setName("basicDataPage");
centerPanel.add(overviewPage, "overviewPage");
centerPanel.add(basicDataPage, "basicDataPage");
The main method, where I create a MainProgram object:
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
MainProgram window = new MainProgram();
window.setVisible(true);
window.initialize();
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
OverviewPage.java
The overview page contains a JTable which gets populated from a database. If the user double-clicks an entry, he gets transfered to the BasicDataPage where he can see the details of the order.
But in order to show the details, I need to somehow transfer the information of the order object into the target class and thats the point I am struggling with!
// I tried several things like object into constructor, static object, creating a method etc...
if (mouseEvent.getClickCount() == 2 && row != -1) {
String workNumberOfOrderObject = (String) table.getValueAt(row, 0);
OrderObject orderObject = GetOrderObject.getOrderObjectFromDatabase(workNumberOfOrderObject);
BasicDataPage basicDataPage = new BasicDataPage();
basicDataPage.recieveOrderObject(orderObject);
workNumberPanel.recieveOrderObject(orderObject);
workNumberPanel.setTxtWorkNumber(workNumberOfOrderObject);
MainProgram.contentCardsLayout.show(MainProgram.centerPanel, "basicDataPage");
}
I tried "sending" the order object to the BasicDataPage via the constructor and set the text in the JTextFields in the BasicDataPage accordingly. This did not work, the textfields simply stayed empty altough I can System.out.println(orderObject.toString()) the recieved object.
BasicDataPage.java
I also tried creating a method receiveOrderObject that I use in the OverviewPage, which should set the textfields of the basicDataPage AND the workNumberPanel, but the fields stay empty:
WorkNumberPanel workNumberPanel = new WorkNumberPanel();
JTextField txtCarWidth = new JTextField(TEXTFIELD_LENGTH);
JTextField txtCarDepth = new JTextField(TEXTFIELD_LENGTH);
JTextField txtCarHeight = new JTextField(TEXTFIELD_LENGTH);
public void recieveOrderObject(OrderObject orderObject){
txtCarDepth.setText(orderObject.getCar_depth());
}
Before posting my question I've read several Q/As here on SO like this:
Accessing UUID from another class in Java ... suggesting to use static for global variables.
I know that static variables are class variables, that all instances can use and only one version exists of. So I tried to send a static object from one class to the other.
But since I am using JTextFields, I had to mix static and non-static content, which either did not work at all or the textfields disappeared.
I have the feeling that I am getting a very basic concept in java wrong, so any help, no matter in which direction, is appreciated!
EDIT:
Based on Reşit Dönüks answer, I was able to fill the textfields by making BasicDataPage and loadBasicData(orderObject) in MainProgram static. Now I can do MainProgram.loadBasicData(orderObject); ... and the textfields in the BasicDataPage get filled as intended.
Is this a valid approach or do I get problems for using static for GUI-Elements? ..... Don't!
I realized that, your are creating BasicDataPage in each double click.
if (mouseEvent.getClickCount() == 2 && row != -1) {
String workNumberOfOrderObject = (String) table.getValueAt(row, 0);
OrderObject orderObject = GetOrderObject.getOrderObjectFromDatabase(workNumberOfOrderObject);
BasicDataPage basicDataPage = new BasicDataPage();
This is the main problem. Do not create BasicDataPage there, just reach the created instance and set the order object to that. My solution is below.
public class MainProgram implements OrderView{
//remove statics here
private JPanel centerPanel = new JPanel();
private CardLayout contentCardsLayout = new CardLayout();
private BasicDataPage basicPage;
public MainProgram() {
//other codes
OverviewPage overviewPage = new OverviewPage();
basicPage = new BasicDataPage();
centerPanel.setLayout(contentCardsLayout);
overviewPage.setName("overviewPage");
basicDataPage.setName("basicDataPage");
centerPanel.add(overviewPage, "overviewPage");
centerPanel.add(basicPage, "basicDataPage");
//oher codes
}
#Override
public void loadOrder(OrderObject order) {
basicPage.recieveOrderObject(orderObject);
contentCardsLayout.show(centerPanel, "basicDataPage");
}
}
public interface OrderView {
public void loadOrder(OrderObject order);
}
public class OverviewPage {
OrderView orderView;
public OverviewPage(OrderView orderView) {
this.orderView = orderView;
}
//in ActionPerformed
if (mouseEvent.getClickCount() == 2 && row != -1) {
String workNumberOfOrderObject = (String) table.getValueAt(row, 0);
OrderObject orderObject = GetOrderObject.getOrderObjectFromDatabase(workNumberOfOrderObject);
orderView.loadOrder(orderObject);
workNumberPanel.recieveOrderObject(orderObject);
workNumberPanel.setTxtWorkNumber(workNumberOfOrderObject);
}
}
As pointed already, Singleton is the way to go. I would just like to point out a mistake in the code provided in the answer before.
private static MainFrameinstance = null;
Rename MainFrameinstance to instance or vice-versa; because the same variable is checked by the getInstance() method.
So I'm having these classes
public class Init {
...
JFrame addStream = new AddStream();
addStream.setVisible(true);
addStream.setLocationRelativeTo(null);
addStream.getData(); //not working
}
public class AddStream extends javax.swing.JFrame {
private String nameData, urlData, qualityData;
/** Creates new form AddStream */
public AddStream() {
initComponents();
}
private void initComponents() {
...
}
private void addActionPerformed(java.awt.event.ActionEvent evt) {
nameData = name.getText();
urlData = url.getText();
qualityData = quality.getSelectedItem().toString();
}
public String[] getData() {
return new String[]{nameData, urlData, qualityData};
}
}
Note the classes arent complete, just snippets.
When the user clicks on the Add button(addActionPerformed) the values get saved to local variables in the AddStream class and get returned by getData().
The problem I'm having is with addStream.getData();, I get "cannot find symbol"
Is there a way to get that data from AddStream JFrame to Init class?
Your problem can be easily fixed by changing this line:
JFrame addStream = new AddStream();
To this:
AddStream addStream = new AddStream();
What's happening in your code is that you're trying to call a method on a JFrame that doesn't exist on a JFrame, it only exists in an AddStream. Even though your JFrame is-a AddStream in this case, the compiler forbids this unless you tell the compiler that it is-a AddStream. And you do that with the code I've shown you.
Another way is to cast it in your call. Imagine you were using your code from above, you could then do this on your last line:
((AddStream) addStream).getData();
In runtime when you do
JFrame addstream = new AddStream();
the object is viewed as a simple JFrame (using the JFrame part of class AddStream).
getData() is only available for AddStream type objects. You could trick the JVM into using the assigned type
if( addstream instanceof AddStream ){
(AddStream) addstream.getData();
} else {
//TODO
}
this is sometime useful when switching between different implementations of the same Interface. Note that the cast is only there to pass the compiler. The runtime checks instanceof only and go aheads if the condition evaluate to true.
I can't get my head round this one. I've tried to adhere to the MVC pattern for the first time and now have difficulties accessing the source of an ActionEvent because the ActionListener is located in a different class. But let the code do the talking...
In the "view":
// ControlForms.java
...
private JPanel createSearchPanel() throws SQLException {
...
comboBoxCode = new JComboBox(); // Field comboBoxCode -> JComboBox()
SwingUtilities.invokeLater(new Runnable() {
public void run() {
AutoCompleteSupport<Object> support = AutoCompleteSupport.install(
comboBoxCode, GlazedLists.eventListOf(jnlCodeArray));
}
}); // Auto-Complete comboBox from GlazedLists
...
public void setComboListener(ComboListener comboListener) {
comboBoxCode.addActionListener(comboListener);
}
...
}
Then, in what I term the controller, I have two different classes:
// Controller.java
public MyController() throws SQLException {
...
addListeners();
}
...
private void addListeners(){
View view = getView();
getView().getControlForm().setComboListener(new ComboListener());
}
and
public class ComboListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
System.out.println("ComboBox listened to! e = " + e.toString());
}
}
Now, e obviously doesn't give the name of the variable (which at the moment I wish it would), so I cannot if test for e.getSource().
My question is thus: is there either a) a way to query (via if for example) the source of e, or b) a less complicated way to get to the variable name?
Many, many thanks in advance for your insights and tips!
Why do you need the name of the variable? Why can't you do the event handling like this
public class ComboListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
JComboBox source = (JComboBox)e.getSource();
//do processing here
}
}
I'd think that if you need to do processing according the variable name, obviously you need different listeners for different combo boxes.
Generally, there are only two situations in which you should use a listener like that: a) you're going to handle a certain event the same way for a bunch of objects, or b) you're only going to use the listener for one object. In the latter case, I'd prefer handling the event locally anyway.
That said, the direct answer to your question is: you shouldn't have to check inside your ActionListener implementation to see whether the appropriate object is the source of the event; you should simply only add the ActionListener to that one object.
One final note: without knowing the specifics of your architecture... generally, MVC will treat all event handling as part of the View (it reduces coupling) and the View will pass commands or method calls or your own events (i.e., not Swing's) to the Controller.