Java to instantiate a class dynamically based on a string name

Question

ok so this has been asked many times and I have looked at various answers but still somehow not able to get this right.

Problem: I have some 5 fragments(non android guys please assume classes) which I need to dynamically instantiate based on what is clicked in a list. I get the string in the click handler. I have named my fragments conveniently. So basically one of my fragments is called SearchResults.java and the corresponding item click will return "SearchResults". So I want to do something like:

public void onClick(View v) {
Class cls = Class.forname(clickedString)   //clickedString = "SearchResults"
//instantiate it as if it were equal to SearchResults sr = new SearchResults().
}

I just want to avoid if/ else or switch cases and looking for a smarter way. I might be missing some very basic core java concepts. Please help.

putting a comment here after some 4 years just in case someone lands up. Fragments should never be instantiated with a constructor. see stackoverflow.com/questions/14654766/…. For a generic class loading by name, reflection is the way. see Asterisk's comment above. — Rajat Sharma
– Rajat Sharma, Commented Mar 3, 2017 at 7:29

epoch · Accepted Answer · 2023-12-27 22:13:00Z

1

Firstly you need fully qualified class names, i.e: your.full.class.path.SearchResults, after that it becomes relatively easy to instantiate assuming a no-args constructor:

Class<?> cls = Class.forName(clickedString);
SearchResults results = (SearchResults) cls.getDeclaredConstructor().newInstance();

Both newInstance() and getDeclaredConstructor() optionally take in the argument and argument types respectively.

edited Dec 27, 2023 at 22:13

answered Dec 13, 2013 at 7:22

epoch

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5 Comments

Rajat Sharma Over a year ago

so you mean clickedString has to be a fully qualified classname? And as luck would have it, my fragments already have a newInstance method. More of a factory thing. Hope that is called and not the default one.

Rajat Sharma Over a year ago

It would work for me I guess. Except that my fragments already have a static 'newInstance' method.

Mohamed AbuIssa Over a year ago

The method is called forName not forname.

user3515670 Over a year ago

newInstance() is deprecated since version 9. What is the current way to do this?

Joop Eggen Over a year ago

@RichardNeumann Class.newInstance is deprecated as it bypasses constructor code. But Constructor.newInstace is fine.

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