code: public static <T> T[] shrink(T[] from, T[] to)
      {
          assert to.length <= from.length;
          System.arraycopy(from, 0, to, 0, to.length);
          return to;
      }
docs: 数组分割
  
  @param from 源
  @param to   目标
  @param <T>  类型
  @return 目标