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Why the method of my jtable getSelectedRow() don't work?

this is my first question, so help me please. I try to save the value of the method getStelectedRow in a type int variable(row) to next can use the method getValueAt(row,column). My problem is the value of my variable, it's -1, and this means the row is not selected, but I'm selecting a row.
The error is the next:
Exception in thread "AWT-EventQueue-0" java.lang.ArrayIndexOutOfBoundsException: -1
If need more details just say me. Thanks.
EDIT:
My code is:
int row = jTablePersonal.getSelectedRow();
String query = "select * from table where id ='"+jTablePersonal.getValueAt(row,0)+"'";
The error point to the variable "row" when I call the method "getValueAt(row,0)"

Seems like a newbie problem. Given your explanation
"My problem is the value of my variable, it's -1, and this means the row is not selected, but I'm selecting a row."
You do not have this code inside a listener, you have like it your constructor or something. You want to have the code inside the listener. Something like
button.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e) {
int row = table.getSelectedRow();
if (row != -1) {
// do something
}
}
});
If you are using the Netbeans GUI Builder tool, you can
From the design view right click the button and go to Events -> Action -> actionPerformed
Go to you source view and you should see some auto-generated code like
jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
}
Write the code there.
You should also take some time to read How to write Event Listeners. GUI Programs are event driven, so you need to learn how to respond to these events by registering listeners

the problem is about getSelectedRow();
getSelectedRow is only work if table is current selected
my suggestion is , make temp variable to get last selectedrow to prevent error ,like
if(table.getSelectedRow()!=-1)
{
int lastselected=table.getSelectedRow();
}

Java Checkbox Action

I have a check box and when I create an Action script from the Netbeans' design, it creates a function like;
private void jCheckBox1ActionPerformed(java.awt.event.ActionEvent evt) {
total=8.99f;
xc = "XCheese";
exTop++;
calculateTotal(total);
updateTextArea();
}
This works perfectly, but I want to set everything to zero when the jCheckBox1 is unchecked, if I uncheck it the way the code is now, no changes appear.

It is an sample of code. Hope it will help you.
private void jCheckBox1ActionPerformed(java.awt.event.ActionEvent evt) {
if(checkBox.isSelected() ){
total=8.99f;
xc = "XCheese";
exTop++;
calculateTotal(total);
updateTextArea();
}else{
// set everything zero here.
}
}

Start by taking a look at How to Use Buttons, Check Boxes, and Radio Buttons
Basically, the ActionListener will be called when ever the check box is selected (checked) or unselected (unchecked). You need to check the state of the check box when ever the method is called.
Take a look at AbstractButton#isSelected which will tell you the (in this case) the checked state of the JCheckBox

Removing all Items from a combo box in Java

I need to remove all items from the combo box
int itemCount = combo.getItemCount();
for(int i = 0; i < itemCount; i++){
combo.removeItemAt(0);
}
This code will remove all items except the last one. It gives a NullPointerException.
How to fix that?

The code in the question would normally work. However, it looks like a threading issue. Another thread may be messing with the items.
However, I sugeest you should better use the removeAllItems(); method:
combo.removeAllItems();

How about JComboBox.removeAllItems()?

You can use
this.combo.removeAllItems();
to remove all the items in JComboBox.

In second line:
combo.removeItemAt(0);
I think instead of 0 it should be i.
do it in reverse order as:
for(int i=combo.getItemCount()-1;i>=0;i--){
combo.removeItemAt(i);
}
But in my case combo.removeAllItems() works fine

use .removeAllItems() methods to remove all items from combo box.

The assumption that it is related to another thread is not always true. It can be the thread itself causing the issue.
This exception may happen because an event is triggered when a combo item is removed and in this event handling method you still refer to combobox items.
For example when you delete somewhere (other than in actionPeformed()) in your code the last item from a combo box with combo.removeItemAt(0) or removeAllItems() then still the event actionPerformed will be fired/executed. But very often the actionPerformed() method contains code to react on user actions (user clicked somewhere on the combobox). So, when the last item has been deleted there is no more item in the combobox and any reference to an item or index in actionPerformed() will cause an exception.
The solution to this is to move the code from actionPerformed() to e.g. mouseClicked() or another event handler depending on what you want to do.

removeAllItems() it does remove all things but after the add data to the combo box it will not show there ,the nullPointException will shows

Use this to remove all the elements from the combo box :
DefaultComboBoxModel model = (DefaultComboBoxModel) ComboBox.getModel();
model.removeAllElements();

Usually it happens because you have an event associated JComboBox. It is solved if you have control item in the JComboBox to act, for example:
jComboBoxExample.addActionListener (new ActionListener () {
public void actionPerformed (ActionEvent e) {
do_run ();
}
});
public void do_run() {
int n=jComboBoxPerfilDocumentos.getItemCount(); <--THIS IS THE SOLUTION
if (n> 0) {
String x = jComboBoxPerfilDocumentos.getSelectedItem (). ToString ();
}
}

How to make a checkbox non-editable in Java?

I have a checkbox. I will obtain one value from a database to determine whether the checkbox can be edited or not. If this value is zero, the checkbox should not be selected. How do I achieve that in code? Please help me out here. This is my code:
String status = "0"; // (obtained from the database)
if(status)
{
// should not be editable - can't be selected.
} else {
// can be selected.
}

If this is REALLY what you want to do instead of using a JLabel with appropriate text and/or icon, you can create an action listener for the checkbox and have it call setSelected:
// the action listener for the checkbox
private void myCheckBoxActionPerformed(java.awt.event.ActionEvent evt)
{
if (status.equals("0")
myCheckBox.setSelected(false);
else
myCheckBox.setSelected(true);
}
To say the least, this isn't an elegant solution, but it does give the appearance that the checkbox isn't editable.

Use the setEnabled method for that.

Actionperformed not triggered for JComboBox

I have an ActionListener attached to a JComboBox(uneditable). Once an item from the JComboBox is selected, I have to make the next button in the frame visible.
The skeleton of the code looks like this:
public void actionPerformed(ActionEvent evt)
{
if(evt.getSource()==jComboBox){
if(jComboBox.getSelectedIndex()==-1)
//Display an alert message
else{
nextButton.setVisible(true);
//Do other actions
}
}
}
It is found that actionPerformed is called only when the second, third, fourth (and so on) items are selected. But actionPerformed is not called when the first item is selected the very first time. But if the first item is selected after selecting other items actioPerformed gets called and the code works fine.
This error appears on some systems and doesn't on other systems. Any help in this regard would be appreciated.
Thanks in Advance!!

This is the normal behavour. The ActionEvent is not fired when you reselect the same item. If you want the event to be fired when you create the combo box then your code should be something like:
JComboBox comboBox = new JComboBox(...);
comboBox.setSelectedIndex(-1); // remove automatic selection of first item
comboBox.addActionListener(...);
comboBox.setSelectedIndex(0);
or
JComboBox comboBox = new JComboBox();
comboBox.addActionListener(...);
comboBox.addItem(...);
comboBox.addItem(...);

Seems like you first condition is a little wrong.
If you want to execute certain code if no item is in your JComboBox, you should check content size : jComboBox.getItemCount()==0 instead of jComboBox.getSelectedIndex()==-1, because selected index can depend upon various conditions, while getItemCount() is only 0 when, well, combo box is empty :-)