Equivalent of C# anonymous methods in Java?

Question

In C# you can define delegates anonymously (even though they are nothing more than syntactic sugar). For example, I can do this:

public string DoSomething(Func<string, string> someDelegate)
{
     // Do something involving someDelegate(string s)
} 

DoSomething(delegate(string s){ return s += "asd"; });
DoSomething(delegate(string s){ return s.Reverse(); });

Is it possible to pass code like this in Java? I'm using the processing framework, which has a quite old version of Java (it doesn't have generics).

[A q on delegates in general in Java](http://stackoverflow.com/questions/44912/java-delegates) — nawfal, Jul 04 '14 at 05:11

Michael Lloyd Lee mlk · Accepted Answer · 2013-10-04T16:31:37.537

Pre Java 8:

The closest Java has to delegates are single method interfaces. You could use an anonymous inner class.

interface StringFunc {
   String func(String s);
}

void doSomething(StringFunc funk) {
   System.out.println(funk.func("whatever"));
}

doSomething(new StringFunc() {
      public String func(String s) {
           return s + "asd";
      }
   });


doSomething(new StringFunc() {
      public String func(String s) {
           return new StringBuffer(s).reverse().toString();
      }
   });

Java 8 and above:

Java 8 adds lambda expressions to the language.

    doSomething((t) -> t + "asd");
    doSomething((t) -> new StringBuilder(t).reverse().toString());

[Google Collections][1] and Groovy[2] might be of interest to you. [1] http://code.google.com/p/google-collections/ [2] http://groovy.codehaus.org/ — Michael Lloyd Lee mlk, Aug 27 '09 at 10:49

Gregory Mostizky · Answer 2 · 2009-08-27T12:27:50.290

13

Not exactly like this but Java has something similar.

It's called anonymous inner classes.

Let me give you an example:

DoSomething(new Runnable() {
   public void run() {
       // "delegate" body
   }
});

It's a little more verbose and requires an interface to implement, but other than that it's pretty much the same thing

edited Aug 27 '09 at 12:27

answered Aug 27 '09 at 10:42

Gregory Mostizky

7,231
1
26
29

score 4 · Answer 3 · answered Aug 27 '09 at 10:48

Your example would look like this in Java, using anomymous inner classes:

interface Func {
    String execute(String s);
}

public String doSomething(Func someDelegate) {
    // Do something involving someDelegate.execute(String s)
}

doSomething(new Func() { public String execute(String s) { return s + "asd"; } });
doSomething(new Func() { public String execute(String s) { return new StringBuilder(s).reverse().toString(); } } });

score 3 · Answer 4 · answered Aug 27 '09 at 10:44

Is it possible to pass code like this in Java? I'm using the processing framework, which has a quite old version of Java (it doesn't have generics).

Since the question asked about the Processing-specific answer, there is no direct equivalent. But Processing uses the Java 1.4 language level, and Java 1.1 introduced anonymous inner classes, which are a rough approximation.

score 3 · Answer 5 · answered Sep 11 '15 at 07:44

For example :

public class Delegate
{
    interface Func
    {
        void execute(String s);
    }

    public static void doSomething(Func someDelegate) {
        someDelegate.execute("123");
    }

    public static void main(String [] args)
    {

        Func someFuncImplementation = new Func() 
        {
            @Override
            public void execute(String s) {
                System.out.println("Bla Bla :"  + s);
            }
        };

        Func someOtherFuncImplementation = new Func() 
        {
            @Override
            public void execute(String s) {
                System.out.println("Foo Bar:"  + s);
            }
        };


        doSomething(someFuncImplementation);
        doSomething(someOtherFuncImplementation);
    }
}

Output :

Bla Bla :123

Foo Bar:123

score 0 · Answer 6 · 2017-08-13T14:03:56.023

0

You have all forgotten here that a C# delegate first of all - is thread safe. These examples are just for a single thread App..

Most of the contemporary Apps are written on multithreaded concept.. So no one answer is the answer.

There is not an equivalent in Java

edited Aug 13 '17 at 14:03

answered Aug 10 '17 at 02:20

It isn't that what you are saying is wrong. It's correct. The problem is, this does not actually answer the question being asked---it just says all the other answers are wrong. Are you saying that there is *not* an equivalent in Java? – Cody Gray - on strike Aug 13 '17 at 13:59
The difference here would for most users be small. I'd even argue that the lack of multicast is a bigger difference between the two. As far as the question is phrased I believe the answers above are correct. All are clear that they are talking about the closest Java has. – Michael Lloyd Lee mlk Apr 25 '18 at 10:46
As references are atomic, the Java version will not crash, but you could have stale data. To make it thread safe all you need to do is add the keyword "volatile". – Michael Lloyd Lee mlk Apr 25 '18 at 10:55

Equivalent of C# anonymous methods in Java?

6 Answers6

Linked

Related