Java Program to implement Min Heap

package lab.heaps;

public class MinHeap
{
  int MAX_SIZE=100;
  int last_position; //last position which is empty
  Comparable[] heap=new Comparable[MAX_SIZE];
  //left child:2n+1, Right child: 2n+2
 
  public MinHeap()
  {
 last_position=0;
  }
 
  public void insert(Object o)
  {
    Comparable data=(Comparable)o;
    Comparable temp;
    int i=last_position;
    last_position++;
    heap[i]=data;
    int parent_i=getParentPosition(i);
  
    if(parent_i==-1)
    { // No more checks needed for first insertion, so return
     return;
    }
  
    while(heap[parent_i].compareTo(heap[i])>0)
    {
     temp=heap[i];
     heap[i]=heap[parent_i];
     heap[parent_i]=temp;
     i=parent_i;
     parent_i=getParentPosition(i);
     if(parent_i==-1)
        {//To avoid array out of bound exception
         return;
        }
    
    }
  
   }
 
  public Object deleteMin()
  {
 Object temp1=heap[0];
 Comparable temp;

 if(last_position==0)
 {
 return null;
 }
 else if(last_position==1)
 {
     heap[0]=null;
     return temp1;
 }

 int i=last_position-1;
 heap[0]=heap[i];
 heap[i]=null;
 i=0;

// If there exists a smaller child for i, then get it.
 int next=getSmallerChild(i);

 while(next!=-1)
 {  
// Go down the heap until you have no smaller child
 temp=heap[i];
 heap[i]=heap[next];
 heap[next]=temp;
 i=next;
 next=getSmallerChild(i);
 }

 last_position--;
 return temp1;
 
  }
 
  public Object getMin()
  {
 return heap[0];
  }
 
  public int getLeftChildPosition(int i)
  {
  return (2*i)+1;
  }
 
  public int getRightChildPosition(int i)
  {
  return (2*i)+2;
  }

  public int getParentPosition(int i)
  {
 if(i==0)
 {
 return -1;
 }
 else if(i%2!=0)
 {
 return (i/2);
 }
 else
 {
 return (i/2)-1;
 }
 
  }
 
  public int getSmallerChild(int i)
  {
//Returns the index of the smaller child, if any of the children are smaller
int left=getLeftChildPosition(i);
int right=getRightChildPosition(i);

if(heap[left]==null && heap[right]==null)
{
return -1;
}
else if(heap[left]!=null && heap[right]==null)
{
if(heap[left].compareTo(heap[i])<0)
   return left;
else
return -1;
}
else if(heap[left]!=null && heap[right]!=null)
{
if(heap[left].compareTo(heap[right])<0 && heap[left].compareTo(heap[i])<0)
{
return left;
}
else if(heap[left].compareTo(heap[right])>0 && heap[right].compareTo(heap[i])<0)
{
return right;
}
else
{
return -1;
}
}

return -1;

  }


}