Java Generics

Last Updated on December 28, 2023 by Ankit Kochar

Java Generics, introduced in Java 5, revolutionized the way developers write code by enabling the creation of classes, interfaces, and methods that operate with different data types. By allowing the use of parameterized types, Java Generics provide flexibility, type safety, and reusability in code. This powerful feature has significantly enhanced the robustness and readability of Java programs, making them more maintainable and efficient.

What are Generics in Java?

Java generic is a feature that allows you to parameterize types in classes, interfaces, and methods. Generics in Java are a way to write code that can work with different data types. They provide a way to define a class, interface, or method that can operate on objects of different types while maintaining type safety. Generics are similar to templates in C++, but they are easier to use.

Java Generic methods and generic classes allow programmers to specify a set of related methods or a set of related types with a single method declaration or a single class declaration, respectively.

Using the Java Generic concept, we could create a generic method for sorting an array of objects, then use Integer arrays, Double arrays, String arrays, and so on to sort the array elements.

Syntax with an example:
The syntax for defining java generics uses angle brackets and a type parameter. The type parameter is a placeholder for the actual type that will be used when an instance of the generic type is created. For example, we define a generic class

public class MyGenericClass {
  private T myVariable;

  public void setVariable(T variable) {
    this.myVariable = variable;
  }

  public T getVariable() {
    return myVariable;
  }
}

In this example, T is the type parameter that can be replaced with any data type when an instance of the MyGenericClass is created. The setVariable method takes a parameter of type T, and the getVariable method returns an object of type T. When we create an instance of MyGenericClass, we can specify the actual type to be used for T, like this:

MyGenericClass stringClass = new MyGenericClass();
stringClass.setVariable("Hello, world!");
String myString = stringClass.getVariable();

In this example, we have created an instance of MyGenericClass that will use String as the type parameter. We then set a string value using the setVariable method and retrieve it using the getVariable method. The type safety is ensured at compile time, as the compiler will not allow us to use any other data type than String with this instance of MyGenericClass.

Advantages of Java Generics

Generics provide several benefits or advantages to Java developers, including:

• Type safety: Generics ensure that the type of data used with a generic class, interface, or method is consistent, which helps prevent runtime errors.
• Code reusability: Generics allow us to write code that can work with different data types, which makes the code more reusable.
• Efficiency: Generics allow us to write code that is more efficient, as it can avoid unnecessary type conversions and reduce the amount of boilerplate code.
• Cleaner code: Generics can make code easier to read and understand, as it can remove the need for casting and other type-related operations.

Types of Java Generics

There are two types of java generics:

1) Generic Class

A generic class is implemented in the same way that a non-generic class is. The only difference is that it includes a section for type parameters. There can be multiple types of parameters, each separated by a comma. Parameterized classes or parameterized types are classes that accept one or more parameters.

Below we have an example with code implementation and explanation

/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;




class GenericClass<T> {
    private T value;
 
    public void setValue(T value) {
        this.value = value;
    }
 
    public T getValue() {
        return value;
    }
}

/* Name of the class has to be "Main" only if the class is public. */
class prepbytes
{
    public static void main (String[] args) throws java.lang.Exception
    {
        // your code goes here
        
        GenericClass<String> stringObj = new GenericClass<>();
        stringObj.setValue("Hello, prepbytes!");
        System.out.println(stringObj.getValue());
        
        
        GenericClass<Integer> intObj = new GenericClass<>();
        intObj.setValue(17);
        System.out.println(intObj.getValue());
        
    }
}

Output

Hello, prepbytes!
17

Explanation
In the above java program, we have defined a Generic class called GenericClass that takes a type parameter T. This type parameter is then used as the type of the value field. The class contains two methods – setValue and getValue. The setValue method takes an argument of type T and sets it as the value of the value field. The getValue method returns the value of the value field. In this example, we have created an instance of the GenericClass class that takes a String type parameter. We have set the value of the value field to "Hello, prepbytes!" using the setValue method.

Now, we have another instance of the GenericClass class that takes an Integer type parameter and test it out. we have created an instance of the GenericClass class that takes an Integer type parameter. We have set the value of the value field to 17 using the setValue method. We then print out the value of the value field using the getValue method.

2) Generic Method

A java generics method is a method that is defined with one or more type parameters, allowing the method to work with different types. The type parameters are specified in angle brackets , and can be used to declare the return type, parameter types, and local variable types within the method. It works exactly like a normal function, except that a generic method has type parameters that are referred to by the actual type. This enables the generic method to be used more broadly. The compiler handles type safety, allowing programmers to code more easily because they do not have to perform lengthy, individual type castings.

Below we have an example with code implementation and explanation

class Main {
  public static void main(String[] args) {

    // initialize the class with Integer data
    DemoClass demo = new DemoClass();

    // generics method working with String
    demo.<String>genericsMethod("Java Programming");

    // generics method working with integer
    demo.<Integer>genericsMethod(25);
  }
}

class DemoClass {

  // creae a generics method
  public <T> void genericsMethod(T data) {
    System.out.println("Generics Method:");
    System.out.println("Data Passed: " + data);
  }
}

Output:

Generics Method:
Data Passed: Java Programming
Generics Method:
Data Passed: 25

Explanation
In the above example, we have created a generic method named genericsMethod.

public  void genericMethod(T data) {...}

Here, the type parameter is inserted after the modifier public and before the return type void. We can call the generics method by placing the actual type and inside the bracket before the method name.

demo.genericMethod("Java Programming");
demo.genericMethod(25);

Note: We can call the generics method without including the type parameter. For example,

demo.genericsMethod("Java Programming");

In this case, the compiler can match the type parameter based on the value passed to the method.

Conclusion
In conclusion, Java Generics have become an integral part of modern Java programming, offering a powerful toolset for developers to write flexible, type-safe, and reusable code. They facilitate the creation of generic classes, methods, and interfaces, enabling the development of more adaptable and scalable applications. By using Generics, developers can write code that is not only clearer and more concise but also less error-prone and easier to maintain. Understanding and leveraging the potential of Java Generics can greatly enhance a developer’s ability to design robust and efficient software solutions.

Frequently Asked Questions(FAQs) about Java Generics

Here are the FAQs on java generics

1. When should I use Java Generics?
Java Generics should be used when you want to create classes, interfaces, or methods that can work with different types in a type-safe manner, enhancing code reusability and readability.

2. What is the purpose of Java Generics?
The primary purpose of Java Generics is to provide type safety, enhance code reusability, and enable developers to create generic classes, methods, and interfaces that can work with different types of data.

3. How do Java Generics improve code quality?
Generics help in writing more flexible and reusable code by allowing the creation of parameterized types. They enable developers to catch errors at compile time rather than runtime and make code more readable by specifying the types used in a more expressive way.

4. What are the advantages of using Java Generics?
Some advantages of Java Generics include type safety, improved code readability, reduced casting, enhanced performance through avoiding unnecessary object creation, and increased reusability of code.

5. Can Generics work with primitive types in Java?
No, Generics cannot directly work with primitive types in Java. Instead, developers can use wrapper classes such as Integer, Double, etc., for primitive types to utilize Generics.