java - Getting error in implementation of heap sort -

i'm trying create , sort heap using array in java. keep getting

exception in thread "main" java.lang.arrayindexoutofboundsexception: 42
@ heapsort.exchange(heapsort.java:28)
@ heapsort.max_heapify(heapsort.java:22)
@ heapsort.build_heap @ heapsort.sort(heapsort.java:36)
@ heapsort.main(heapsort.java:46)

i'm not sure error coming from.

public class heapsort {     public static int n;     public static int[] a;     public static int largest;      public static void build_heap(int[] a){         n = a.length-1;         for(int = n/2; >= 0; i--){             max_heapify(a,i);         }     }     public static void max_heapify(int[] a,int i){         int left = 2*i;         int right = 2*i +1;          if(left <= n && a[left] > a[i])             largest = left;         if(right <=n && a[right] > a[largest])             largest = right;         if(largest != i)             exchange (a[i],a[largest]);         max_heapify(a,largest);     }       private static void exchange(int i, int j) {         int temp = a[i];         a[i] = a[j];         a[j] = temp;         // todo auto-generated method stub      }     public static void sort(int[] a0){         = a0;         build_heap(a);          for(int = n; > 0; i--){             exchange(0,i);             n = n-1;             max_heapify(a,0);         }     }     public static void main(string[] args){         int[] a1 = {3,55,6,42,34,56,34};         sort(a1);         for(int = 0; < a1.length; i++){             system.out.print(a1[i] + " ");         }     } } 

you getting error in exchange(). parameters i , j method indexes of array a. but, calling method exchange(a[i],a[largest]) passing value of array @ indexes i , largest instead of passing actual indexes i , largest method.

try calling exchange exchange(i,largest)