如何在java中将函数作为参数传递以多次运行它

Question

Sorry to ask that question I've seen that it has been asked a lot but not the way I'm think it.

My goal is to make a retry function that would loop 'n' amount of time to try to run the method I'm passing as parameter.

So in this case I want to run the function "myFunction()" but I know that sometimes the returned value is false and I want to run it until the return value is true.

That's how I would like it to run :

public static void main (String [] args){
    boolean did work = retry (myFunction(),5)
    if(didwork){
        System.out.println("I found my stuff");
    } else {
        System.out.println("I didn't found my stuff");
    }
}

public boolean retry (Function function, int loopTry){
    boolean success = false;
    for(int i=0 ; i<loopTry ; i++){
        success = function.run();
        if(success){
            break;
        }
    }
    return success;
}

public boolean myFunction(){
    boolean found = false;
    //do stuff
    if(stuff){
        found = true;
    }
    return found;
}

I know that it's not possible (at least in java 7 maybe in 8)

I've seen some answers suggesting to create an object for the specific function etc ... but that's wouldn't make the retry function generic since I would need to remake an object for each method that I would like to retry and that's not what I want.

So I would like to know if there is a "clean" way to do it (even in java 8) or not ?

Thank you

Answer 1

You could try reflection here:

Eg:

public static void main(String[] args) throws NoSuchMethodException, SecurityException, IllegalAccessException,
            IllegalArgumentException, InvocationTargetException {

  Method method = Test.class.getMethod("myFunction");

  boolean didwork = retry(method, 5);
  if (didwork) {
      System.out.println("I found my stuff");
  } else {
      System.out.println("I didn't found my stuff");
  }

}

public static boolean retry(Method method, int loopTry)
        throws IllegalAccessException, IllegalArgumentException, InvocationTargetException {

  boolean success = false;
  for (int i = 0; i < loopTry; i++) {
    success = (Boolean) method.invoke(null);
    if (success) {
      break;
    }
  }
  return success;
}

public static boolean myFunction() {
  boolean found = false;

  //do stuff
  if(stuff){
     found = true;
  }

  return found;
}

Answer 2

You could just add a while loop to myFunction() which "retries" inside the function. This would be just one addtional line. Maximum two or three if you define the maximum number of tries as n. In the second case you've recreated the effect of either trying until you get a true or until the number if tries is reached.