What Is Hierarchy of Data Type in Java?


Scott Campbell

In Java, the hierarchy of data types is an important concept to understand. It refers to the arrangement of data types in a way that shows their relationships and allows for conversions between them.

Primitive Data Types

Java has eight primitive data types:

  • byte: Used to store small integers.
  • short: Used to store integers that don’t require much memory.
  • int: Used to store whole numbers.
  • long: Used to store large integers.
  • float: Used to store decimal numbers with single precision.
  • double: Used to store decimal numbers with double precision.
  • boolean: Used to store true/false values.
  • char: Used to store single characters.

Reference Data Types

In addition to the primitive data types, Java also has reference data types. These are more complex and can refer to objects or arrays:


An object is an instance of a class. It can hold both data and methods. Examples of reference data types for objects include:

  • String: Represents a sequence of characters.
  • Date: Represents a specific moment in time.
  • ArrayList: Represents a resizable array-like structure.
  • Scanner: Represents a tool for reading input from various sources.


An array is a collection of elements of the same data type. Examples of reference data types for arrays include:

  • int[]: Represents an array of integers.
  • double[]: Represents an array of decimal numbers.
  • String[]: Represents an array of strings.

Type Conversion and Casting

The hierarchy of data types in Java allows for type conversion and casting between compatible data types. When converting from a smaller data type to a larger one, it can be done implicitly. For example, converting from an int to a double:

int myInt = 10;
double myDouble = myInt; // Implicit conversion

However, when converting from a larger data type to a smaller one, it needs to be done explicitly using casting:

double myDouble = 10.5;
int myInt = (int) myDouble; // Explicit casting

Note that when casting from a floating-point number to an integer, the decimal part is truncated.


Understanding the hierarchy of data types in Java is essential for effective programming. It allows for proper handling and conversion of different types of data. By using the appropriate data type for each variable or object, you can ensure efficient memory usage and avoid potential errors.

So remember to choose your data types wisely and make use of the hierarchy when working with different types of values in Java!

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