public RegisterSpec get(int reg) {
    try {
      return specs[reg];
    } catch (ArrayIndexOutOfBoundsException ex) {
      // Translate the exception.
      throw new IllegalArgumentException("bogus reg");
    }
  }
Gets the element with the given register number, if any.

@param reg {@code >= 0;} the desired register number
@return {@code null-ok;} the element with the given register number or {@code null} if there is
    none
android/android_framework/dex-maker/src/main/java/com/android/dx/rop/code/RegisterSpecSet.java