Create Swing component from string

Question

How can I create a Swing component ( such as a JPanel or JButton ) dynamically from a string that refers a component name?

For example;

String c = "JPanel";

(c) com = new (c)(); // It must be equivalent JPanel com = new JPanel();

or a function like this;

Object c = Object.createObjectFromString(c);

Thanks

Why would you want to do this? All the validation you are going to need will just make your code unreadable. — Hidde, Oct 21 '12 at 19:09
I suppose this could be done with reflection, but could you give us more context here? Why do you need/want this functionality? — Hovercraft Full Of Eels, Oct 21 '12 at 19:09
Well, it can be done with `Class.forName()` and then calling appropriate constructor, but why would you need this ? — Andrew Logvinov, Oct 21 '12 at 19:10
@PrototypeStark: could be, but I'd like to know, because if not, there may be much better ways to solve the overlying problem (whatever that currently is). — Hovercraft Full Of Eels, Oct 21 '12 at 19:12
Using a combination of generics and reflection would probably work. — luiscubal, Oct 21 '12 at 19:13
@HovercraftFullOfEels a better solution may not necessarily be an easy one. I think he can easily solve that with a preprocessor. — Aniket Inge, Oct 21 '12 at 19:13
@HovercraftFullOfEels `public T createObject(Class type) { ... }`, maybe? Or `public T createObject(String typeName)`. Of course, if he really has zero clue of what the type will be then pure reflection would be the only way to go - this smells a lot like dynamic typing. — luiscubal, Oct 21 '12 at 19:15
@ALL: I have a xml that contains components name and their properties. I read this data and want to render dynamically. — miqbal, Oct 22 '12 at 15:07

Óscar López · Accepted Answer · 2012-10-21T22:04:34.467

It can be done, using the Reflection API:

Class<?> klazz = Class.forName("javax.swing.JPanel");
JPanel panel = (JPanel) klazz.newInstance();

Notice that you have to pass a fully-qualified class name to the forName() method, and that at some point (be it as a type parameter to Class<?> or by using a cast like in the above code) you'll have to explicitly specify the class that you intend to instantiate. Or if you don't care about the exact type of the instance, you can simply do this:

Object obj = klazz.newInstance();

Also, I'm assuming that the class has defined a no-arguments constructor. If that is not the case, you'll have to create a Constructor object first before instantiating the new object:

Class<?> klazz = Class.forName("javax.swing.JPanel");
Constructor<?> constructor = klazz.getDeclaredConstructor(/* parameter types */);
JPanel panel = (JPanel) constructor.newInstance();

Reimeus · Answer 2 · 2012-10-21T19:20:47.750

2

You could use reflection:

// c is JPanel for instance
Sting componentClassName = "javax.swing." + c; 
JPanel panel = (JPanel)Class.forName(componentClassName).newInstance();

Using Class.newInstance() requires a the component you are creating to have a default constructor but this is provided by most if not all the standard Swing components.

edited Oct 21 '12 at 19:20

answered Oct 21 '12 at 19:10

Reimeus

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But, I don't know what is it type. It could be JButton – miqbal Oct 21 '12 at 19:11
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@miqbal: that's where the String parameter comes in. Use a variable there and your problem is solved. – Hovercraft Full Of Eels Oct 21 '12 at 19:12

score 0 · Answer 3 · edited May 23 '17 at 12:24

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see here How to create an object from a string in java how to eval a string and Creating an instance from string in java. But I would also suggest you to write your own preprocessor if you want it to evaluate in 1 single line. That's what C/C++ preprocessors do.

edited May 23 '17 at 12:24

Community

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answered Oct 21 '12 at 19:17

Aniket Inge

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Create Swing component from string

3 Answers3