Calling a method from an array-list of objects

Question

I'm just starting with Java and I'm having trouble with the following code. I was using something like this to call the non-static apply method from a static method, but I dont think its very efficient. I set an array list of the rules that need to be applied but I can't get it to work.

    ClassificationRule rules = new RuleFirstOccrnc();
    ClassificationRule rules1 = new RuleOccrncCount();
    rules.apply(aUserInput);
    rules1.apply(aUserInput);

I'm getting this error when trying to call the apply() method from ClassificationRule "The method apply(String) is undefined for the type ArrayList". Any help would be greatly appreciated!

package tweetClassification;

import java.util.ArrayList;

public class PrioritRuls {

    //Set of rules to be applied
    final static ArrayList<ClassificationRule> rulesA
        = new ArrayList<ClassificationRule>();

    static{
        rulesA.add( new RuleFirstOccrnc() );
        rulesA.add( new RuleOccrncCount() );
    }

    // ******************************************* 
    public static void prioritize( final String aUserInput ){

        rulesA.apply(aUserInput); //ERROR
       // The method apply(String) is undefined
       // for the type ArrayList<ClassificationRule>
        }
} 
package tweetClassification;

public class ClassificationRule {

     // *******************************************
     public void apply (final String aUserInput) {  

        apply( aUserInput );
        }
}

Chris Thompson · Accepted Answer · 2012-04-08 23:20:42Z

3

Right, because you're calling the apply method on the array list object, not the contents of the array list.

Change it to something like

rulesA.get(0).apply()

Or, if you want to call it on every element, you need to iterate through the list.

for (ClassificationRule rule:rulesA){
  rule.apply(aUserInput);
}

answered Apr 8, 2012 at 23:20

Chris Thompson

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1 Comment

tom3322 Over a year ago

Thanks for the fast response that makes perfect sense. Greatly appreciated!

amit · Accepted Answer · 2012-04-08 23:26:25Z

1

You are trying to invoke apply() on the ArrayList instead on the ClassificationRule object. ArrayList does not have this method, so as expected - you get a compilation error.

You might want to iterate the ArrayList and apply() on each ClassificationRule object with a for-each loop:

for (ClassificationRule rule : rulesA) rule.apply(aUserInput)

or to apply() on a specific element:

rulesA.get(someIndex).apply(aUserInput)

One more thing:

public void apply (final String aUserInput) {  
   apply( aUserInput );
}

will cause an infinite recursive calls to apply() [well, not exactly infinite, it will throw eventually an exception]. This is not the error you are currently having, since this is run-time error, while you are still stuck at compile-time errors.

edited Apr 8, 2012 at 23:26

answered Apr 8, 2012 at 23:20

amit

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2 Comments

amit Over a year ago

You are most welcome @tom3322, and good luck! don't forget to accept one of the answers later.

tom3322 Over a year ago

about apply() how do you suggest I fix that, i'm not getting any errors.. I'm trying to call the non-static apply() method of the rules using inheritance.

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