Binary Search Method Array Java

Question

I am trying to efficiently search weather a subclass implements a method that I have the name of in a string called _szMethodName . I can get an array of all the methods that the subclass implements by doing Method[] _arrClassMethodsList = class.getMethods(); . I can then compare the name of the method to the stringName of the function that I am looking for to determine weather or not the class implements that particular method. Currently I have this working in a for loop but this gets slow as the subclass grows.

For Loop implementation:

for (Method method : class.getMethods()){
       if(method.getName().equals(_szMethodName)){
          //method exists in subclass
          break;
      }
}

The array of methods from class.getMethods() is sorted alphabetically. (Only in Java >=7). I was hoping that I could leverage this by using a binary-search or some other optimization on the array instead of using the for loop. However, I have not yet been able to figure out how to implement Java's binary search function on the array. I have tried using comparator or and comparable but have not yet had success. My most recent implementation of comparator is below but has errors that I have not yet been able to resolve.

Current attempt using comparator:

Comparator<Method> c = new Comparator <Method>() {
    public int compare(Method method, String string) {
        return method.getName().compareTo(string);
    }
};

Method[] _arrClassMethodsList = class.getMethods();
int index = Arrays.binarySearch(_arrClassMethodsList, _szMethodName, c);

Any help or examples on how to get this working would be greatly appreciated. Thanks!

Answer 1

Why don't you use the method http://docs.oracle.com/javase/6/docs/api/java/lang/Class.html#getMethod%28java.lang.String,%20java.lang.Class...%29 to directly get the method if available and let the JVM do the job efficiently for you?

BTW, the documentation of getMethods says: "The elements in the array returned are not sorted and are not in any particular order ". The binary search needs sorted data. That means you first need to sort the array.

NOTE: you should have a look to that method getMatchingAccessibleMethod that probably does what you expect.

Answer 2

It would appear that the only real way to do this is to re-implement Binary search pulling out the method name during the search. My final implementation is below. Thanks for all the help everyone.

public final Method NOT_FOUND = null;
private Method findMethodInDelegateClassWithParameters (String _szMethodName)
{
    @SuppressWarnings("rawtypes")
    Class _cDelegateClass = m_oDelegate.getClass();

    //Get and sort array for binary search if not done, ensure methods are alphabetical before Java 7 
    if (_arrSortedMethods==null){
        _arrSortedMethods = _cDelegateClass.getMethods();   
        Arrays.sort(_arrSortedMethods, new Comparator<Method>() {
               public int compare(Method m1, Method m2) {
                   return m1.getName().compareTo(m2.getName());
               }
        });
    }

    return binarySearchForMethodNamed(_arrSortedMethods, _szMethodName);
}

public Method binarySearchForMethodNamed(Method[] _arrMethods, String _szMethodName) {
    int left = 0;
    int right = _arrMethods.length - 1;
    return binarySearchMethods(_arrMethods, _szMethodName, left, right);
    }

private Method binarySearchMethods(Method[] _arrMethods, String _szMethodName, int left, int right) {
    if (right < left) {
            return NOT_FOUND;
    }

    int mid = (left + right) >>> 1;
    String _szArrayMethodName = _arrMethods[mid].getName();
    if (_szMethodName.compareTo(_szArrayMethodName)>0) {
            return binarySearchMethods(_arrMethods, _szMethodName, mid + 1, right);
    } else if (_szMethodName.compareTo(_szArrayMethodName)<0) {
            return binarySearchMethods(_arrMethods, _szMethodName, left, mid - 1);
    } else {
            return _arrMethods[mid];
    }               
}