What Is a Generic Data Type in Java?


Larry Thompson

A generic data type in Java is a way to create classes, interfaces, and methods that can work with any data type. It allows you to write reusable and type-safe code by making the code more flexible and adaptable. With generic data types, you can create classes or methods that can work with different types of objects without sacrificing type safety.

Why Use Generic Data Types?

Using generic data types offers several benefits:

  • Type Safety: Generic data types provide compile-time type checking, ensuring that the correct types are used. This helps prevent runtime errors caused by incompatible data types.
  • Code Reusability: With generics, you can write code that can be used with multiple data types without duplicating the code.

    This promotes code reuse and reduces redundancy.

  • Flexibility: Generic data types allow you to create flexible classes and methods that can work with different object types. This makes your code more adaptable and versatile.

Syntax of Generic Data Types

The syntax for creating a generic class in Java is as follows:

class ClassName<T> {
     // Class body

The “T” inside angle brackets represents the type parameter. It can be replaced with any valid identifier, but it is common convention to use “T” to denote a generic type. Multiple type parameters can also be defined using commas, such as “T, U, V“.

To use a generic class or method, you need to specify the actual type argument when creating an instance or invoking the method.

Example: Generic Class

Let’s consider an example of a generic class called Box that can hold objects of any type:

class Box<T> {
     private T value;

     public Box(T value) {
         this.value = value;

     public T getValue() {
         return value;

In the above example, the class Box<T> is a generic class with a type parameter “T“. The constructor and methods of the class can work with the generic type “T“. When creating an instance of the Box class, you need to provide the actual type argument.


Box<String> stringBox = new Box<>("Hello");
String stringValue = stringBox.getValue();

Box<Integer> intBox = new Box<>(123);
Integer intValue = intBox.getValue();

In this example, we create two instances of the Box class. One holds a string value, and the other holds an integer value. The actual type arguments (“<String>” and “<Integer>“) are specified when creating the instances.

Limits on Generic Types in Java:

In Java, primitive types (e.g., int, char, etc.) cannot be used as type arguments for generics.

However, you can use their corresponding wrapper classes (e., Integer, Character, etc.) instead.

Additionally, it is important to note that generic types are erased at runtime, meaning that the actual type arguments are not available at runtime. This is known as type erasure. However, during compile-time, the compiler performs necessary checks to ensure type safety.


In summary, a generic data type in Java allows you to create reusable and type-safe code that can work with different types of objects. It provides benefits such as type safety, code reusability, and flexibility. By using generic data types effectively, you can write more robust and adaptable Java programs.

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