In Java, objects are one of the main building blocks of programming. An object data type is a type of data in Java that is created using a class. The class defines the data fields and methods that the object can use.

An object is an instance of a class, which means it has been created based on the class definition. Objects have attributes called instance variables, which hold their state, and methods, which define their behavior.

There are several pre-defined object data types in Java, such as String, Integer, and Double. These data types are used to represent common real-world objects and concepts, such as text, numbers, and decimals.

In addition to pre-defined object data types, Java allows programmers to create custom object data types by defining their own classes. This allows for great flexibility and control over the data being manipulated, as well as the behavior of the objects themselves.

Overall, object data types provide a powerful tool for organizing and managing data in Java programs, allowing for efficient data manipulation and abstraction of complex systems.