Weka - Get "Accuracy percentage"? -

i'm working on web service writen in java use weka algorith j48 classify atributes. first builds classifier , classifies instance using classifier tree.

this part of code have classifydata method

fc.buildclassifier(train); (int = 0; < test.numinstances(); i++) { double pred = fc.classifyinstance(test.instance(i)); predicated = (test.classattribute().value((int) pred)); } 

being fc filteredclassifier set, being train data used build classifier , test instance classify i'm not sure if code i'm doing classification, if confirm nice.

what want "accuracy percentage". don't know if called don't know how else reffer it. basicly want return accuracy percentage of classify result. imagine have simple tree has 2 classifications, "1" or "2". imagine classify instance , result "2". want return how accurate instance "2", , says accuracy says probability of being "2"

i hope made myself clear because kinda new me aswell

for have use distributionforinstance() method:

double[] probabilitydistribution = fc.distributionforinstance(test.instance[i]) 

then if have 2 class values "1" , "2" (and added attribute/class values in order class attribute), can probabilities given test instance of 1 of 2 class values by:

// probability of test instance beeing "1" double classatt1prob = probabilitydistribution[0]; // probability of test instance beeing "2" double classatt2prob = probabilitydistribution[1];