Append a number in the end of a variable name in java

Question

Suppose that I have a lot of variables defined in my code with names such as this

public javax.swing.JPanel BenderPanel1;
public javax.swing.JPanel BenderPanel2;
public javax.swing.JPanel BenderPanel3;
etc...

So their general type is like this: BenderPanel"NUMBER".

I want to access some of them and set their visibility with .setVisible(false); but the number of those panels which I want to access is user-defined on run time.

Is there any possible way through a library to append a number to the end of each variable in order to access it in a for loop, like this:

for (int i=1; i<=UserInput; i++)
{
     BenderPanel"i".setVisible(false); // Watch this "i" right there.
}

WITHOUT the need to add them on ArrayList first and do it with the obvious way?

use array instead of doing this way,array is what you need – Cris Jan 18 '13 at 09:33 — Cris, Jan 18 '13 at 09:33
(And don't use public variables, either...) – Jon Skeet Jan 18 '13 at 09:42 — Jon Skeet, Jan 18 '13 at 09:42

T.J. Crowder · Accepted Answer · 2013-01-18T10:36:16.677

5

You can't create members dynamically in Java (you can access them dynamically via reflection, but there's no need for it here).

Rather than having

public javax.swing.JPanel BenderPanel1;
public javax.swing.JPanel BenderPanel2;
public javax.swing.JPanel BenderPanel3;

have

public javax.swing.JPanel[] BenderPanels;

or

public List<javax.swing.JPanel> BenderPanels;

Then you can loop through them with an enhanced for loop.

for (javax.swing.JPanel panel : BenderPanels) {
    // ...
}

edited Jan 18 '13 at 10:36

answered Jan 18 '13 at 09:35

T.J. Crowder

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Why he can't do this in Java if he can with Reflection? – Michał Kupisiński Jan 18 '13 at 09:53
1

@emka86: You can't dynamically create new variables with reflection. You *can* access the existing data members of an object instance using reflection, though, that's true. – T.J. Crowder Jan 18 '13 at 10:35
yes, that true but your previous answer before edit just say that he "can't do that in Java" – Michał Kupisiński Jan 18 '13 at 10:54

score 2 · Answer 2 · answered Jan 18 '13 at 09:34

2

If you really do not want to store your objects in a data structure like e.g. an ArrayList, I would recommend to use the Reflection API.

Especially interesting for you should be the fields.

Btw: According to the Java Naming Conventions, variable names shouldn't start with capital letters.

answered Jan 18 '13 at 09:34

RoflcoptrException

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Thanks for the answer. Also thank you for reminding me JavaNamingConventions which I use almost everywhere but GUI design :D – Theocharis K. Jan 18 '13 at 09:36

score 0 · Answer 3 · answered Jan 18 '13 at 09:38

I'll provide you an idea about using Reflection:

public class YourClassContainer extends ... {

public javax.swing.JPanel BenderPanel1;
public javax.swing.JPanel BenderPanel2;
public javax.swing.JPanel BenderPanel3;
....
public javax.swing.JPanel BenderPanelXXX;

....

//to access all of them:

for (Field field : YourClassContainer.class.getFields()) {
    if (field.getName().startsWith("BenderPanel")) {
        ((javax.swing.JPanel)field.get(YourClassContainer.this)).setVisible(false);
    }
}

}

Well this certainly looks uglier and more code than `ArrayList`, so I will just go for the `ArrayList`. +1 for the example though. — Theocharis K., Jan 18 '13 at 09:39

Michał Kupisiński · Answer 4 · 2013-01-18T09:52:24.957

Use Reflection in that Way:

YourClasss instance; // this instance has those all JPanel fields
Method setVisible = JPanel.class.getMethod("setVisible", new Class[] {Boolean.class});

List<String> numberOfFieldList = getNumbersOfFieldsToSetInvisible(); 

for (String number : numerOfFieldList) {
  Field benderPanelField = YourClass.getField("BenderPanel" + number);
  Object fieldInYourInstance = benderPanelField.get(instance);
  setVisible.invoke(fieldInYourInstance, Boolean.FALSE);
}

Maybe it will help.

d.raev · Answer 5 · 2013-01-21T07:54:21.883

-1

Simple example using your setup:

    List<Integer> visibleItems = new ArrayList<Integer>();

    JPanel[] myPanels = new JPanel[]{BenderPanel1, BenderPanel2, BenderPanel3};

    for (int i = 0; i < myPanels .length; i++) {
        myPanels[i].setVisible(false);
        if(visibleItems.contains(i) ){
            myPanels[i].setVisible(true);
        } 
    }

edited Jan 21 '13 at 07:54

answered Jan 18 '13 at 09:47

d.raev

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Append a number in the end of a variable name in java

5 Answers5