Create instance of generic class member: Class

I want to make a generic class which stores a pool of temporary objects (such as 2D vector Vec2d ) so that I don't have to dynamically allocate them during my simulations. Based on these answers [1] [2] I come to this solution:

import java.lang.reflect.Array;

class TempPool<T>{
  T[] objs;

  public TempPool(Class<T> c, int n) {
    T[] a = (T[])Array.newInstance(c, n);                // initialize the array
    try{ // Compiler forces me to use try fo handling                     
      for(int i=0; i<n; i++) a[i]=(T)c.newInstance();   // initialize fields in the array
    }catch(Exception e){
      System.out.println("Exception thrown  :" + e +" in TempPool()" );
    }
    objs = a;
  }

  T    borrow(  ){ return objs[icur++];    };
  void repay(T o){ 
    if( o != objs[icur] ) objs[-1]=null; // Throws exeption
    }else{ icur--; }
  }

But when I try to use

class Vec2d{ double x,y; }

tmpVec2d   = new TempPool       (Vec2d.class,10);   // tried both
//tmpVec2d = new TempPool<Vec2d>(Vec2d.class,10);   // tried both

it it throws exception Exception thrown :java.lang.InstantiationException: Boulders_rigid$Vec2d in TempPool()