# Overview

By default

*DateTime*

class in Joda-Time API is immutable. However Joda-Time gives an option to create Mutable version of

*DateTime*

called

*MutableDateTime*

.

This article describes the usage of

*MutableDateTime*

.

#### Modify Fields

Use setter methods to modify fields in

*MutableDateTime*

#### Add Fields To MutableDateTime

Fields can be added to

*MutableDateTime*

using the following ways:

- Using add..() methods to directly add the value of field
- Adding Duration: Using the following 3 ways:
- Using DurationFieldType
- Directly adding Duration
- Adding Duration in Millis

- Adding Period

#### Perform Rounding Operations

Joda-Time API provides supports for rounding off

*DateTime*

to the nearest field.

In particular, the following types of rounding are supported:

- Floor: Round to the nearest floor
- Ceiling; Round to the nearest ceiling
- Half Floor: Round to the floor if the value of the field is closer to floor or exactly halfway. Else round to ceiling
- Half Ceiling: Round to the floor if the value of the field is closer to floor or exactly halfway. Else round to ceiling
- No Rounding

To start, click on the next arrow. If you find anything missing in the tutorials then please drop in your comments.