ObjectiveC blocks Java equivalent

Question

There's a feature of the Apple Objective-C language which is really useful to me: I can pass code blocks as argument in methods.

I'd like to do that in Java, too. Something like:

myManager.doSomethingInTransaction(function() {
   dao.save();  
});

So the myManager object will execute my code between a startTransaction() and a endTransaction() methods.

Is there a way to get that in Java?

The simple answer is "no", there's no functionality like that in Java. — Aleks G, Apr 03 '12 at 14:46

score 43 · Accepted Answer · answered Apr 03 '12 at 14:46

Unfortunately, Java doesn't support this. But you can get similar functionality with anonymous classes.

To do so, first you define an interface:

interface TransactionAction {
    public void perform();
}

doSomethingInTransaction should then be defined to take a TransactionAction as an argument.

Then, when you call it, do this:

myManager.doSomethingInTransaction(new TransactionAction() {
    public void perform() {
        dao.save();
    }
});

score 13 · Answer 2 · answered Apr 03 '12 at 14:49

13

No this does not exist in Java (yet). A workaround is to use the Runnable interface:

myManager.doSomethingInTransaction(new Runnable() {
    public void run() {
        dao.save();  
    }
});

or any interface with a single method will do.

answered Apr 03 '12 at 14:49

Guillaume Polet

47,259
4
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This is the best solution! – Mr. Cobblepot Oct 02 '13 at 11:16

John-Paul Gignac · Answer 3 · 2016-01-09T06:26:28.260

4

This is now possible in Java 8 using a lambda expression:

myManager.doSomethingInTransaction(() -> {
    dao.save();  
});

Or more tersely:

myManager.doSomethingInTransaction(() -> dao.save());

Your implementation of doSomethingInTransaction should accept a Runnable parameter, or any other single-method interface with a matching method signature.

You can find Oracle's documentation here: https://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html

edited Jan 09 '16 at 06:26

answered Jan 09 '16 at 05:41

John-Paul Gignac

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2
8

2

This could even be simplified to `myManager.doSomethingInTransaction(dao::save);` – Palle Jan 09 '16 at 05:47
Ho can I make a reference to lambda? – Neftanic Jun 13 '20 at 10:43

score 4 · Answer 4 · answered Apr 03 '12 at 14:53

you can use an Interface like

interface CodeBlock {
    void execute();
}

the function would look like

someType functionToBeExecuted(CodeBlock cb) {
    ...
}

it would be called like

functionToBeExecuted(new CodeBlock() {
   void execute() {
       // blah
   }
});

But if your code should be able to access variables or fields in will be more specialized. Also performance will be lower this way because of the new objects.

ObjectiveC blocks Java equivalent

4 Answers4