Creating a Generic Array in Java

A Generic Array in Java refers to an array defined using generics, allowing us to store elements of a specified type. If you are new to generics, Generics in Java is a feature that enables developers to create classes, interfaces, and methods with type parameters. To create a generic array in Java, we have multiple methods such as Object arrays, Reflection, or Collections like ArrayList.

In this blog, we will learn how to create a generic array in Java using different methods or approaches.

Table of Contents:

• What are Generics in Java?
• What is a Generic Array in Java?
• Syntax for Creating a Generic Array in Java
• Methods to Create a Generic Array in Java
  • Method 1: Using Object Array
  • Method 2: Using Reflection Class
  • Method 3: Using ArrayList in Place of an Array
  • Method 4: Using LinkedList
  • Method 5: Creating Generic Arrays From Streams
• Advantages and Disadvantages of Generic Arrays in Java
  • Advantages of Generic Arrays in Java
  • Disadvantages of Generic Arrays in Java
• Conclusion

What are Generics in Java?

Generics in Java is a feature that allows us to create classes, methods, and interfaces that can work with different data types while ensuring type safety. It helps catch errors at compile time and removes the need for explicit type casting. It prevents ClassCastException by ensuring that only specific types are used.

What is a Generic Array in Java?

A generic array is used to store elements of a specified type while maintaining type safety and code reusability. It allows developers to write flexible and reusable code without specifying a fixed data type.

Since Java does not allow direct creation of generic arrays due to Type Erasure, we use Object arrays, Reflection (Array.newInstance()), or Collections (ArrayList<T>) as alternatives.

Syntax for Creating a Generic Array in Java

Creating a generic array in Java is similar to creating regular arrays, but there is one key difference: you must explicitly specify the type parameter. This ensures that only specific types of objects can be stored in the array.

For example, if you want to create an array that contains Integers, the syntax looks like this:

Integer[ ] numbers = new Integer[5];

However, Java does not allow direct creation of generic arrays like T[ ] array = new T[5];. Instead, to create a generic array, you can use an Object array and use it to the required type:

Now, use this GenericArray class to create an instance of the class, and store values of different data types(like: strings, Integers, etc.)

Methods to Create a Generic Array in Java

Here are the following methods to create a generic array in Java:

Method 1: Using Object Array

Java does not allow us to directly create generic arrays due to type erasure, we can use an Object array. With the help of an object array, we can store a specific type of value in the array.

Example: Creating a Generic Array Using an Object Array

Output:

Explanation: In the above code,

• We use an Object array (Object[] array) to store elements of type T.
•  The set() method assigns a value to a given index.
• The get() method retrieves the value based on the index.

Method 2: Using Reflection Class

We can use the Reflection API to create a generic array. The java.lang.reflect.Array class allows us to dynamically create an array of a specific type at runtime.

Example:

Output:

Explanation: In the above code, we have created a generic array, in which we can store values of any data type. We have implemented a setter and getter function to set the value and get data from it, respectively.

Method 3: Using ArrayList in Place of an Array

You can also use ArrayList to create a generic array in Java. ArrayList is better than an array because we can create a dynamic array using ArrayList instead of an array. 

Example:

Output:

Explanation: We have created a generic array using ArrayList, it stores elements dynamically, which allows easy addition and retrieval of elements.

Method 4: Using LinkedList

You can also use a LinkedList to create a generic collection in Java. Unlike arrays, LinkedList provides dynamic memory allocation, allowing efficient insertions and deletions. Therefore, we do not need to worry about the size of the linked list.

Example: Generic LinkedList Implementation

Output:

Explanation: In the above code, we have used LinkedList to create a generic array in Java.

• The add(T value) method inserts elements dynamically.
• The get(int index) method retrieves elements, while size() returns the number of stored elements.

Method 5: Creating Generic Arrays From Streams

Java Streams API provides an efficient way to create and manipulate generic arrays. The toArray() method in streams can be used to convert a collection or stream into an array dynamically.

Example 1: Using toArray()

Output:

Explanation: In the above code, we have created a Stream of Strings using Stream.of(). The toArray() method converts the stream into an Object array. Then we iterate over the array and print the elements.

Example 2: Using toArray(IntFunction<T[ ]>) to Get a Typed Array

Output:

Explanation: In the above code, we have used the toArray(Integer[]::new) method, which ensures that the returned array is strongly typed as Integer[] instead of Object[].

Advantages and Disadvantages of Generic Arrays in Java

Here are the following advantages and disadvantages of the generic array in Java:

Advantages of Generic Arrays in Java

• Prevents Errors: With the help of a generic array, only the correct type of data can be stored, which prevents errors.
• Reusable Code: With the help of a generic array, the same code can work for different data types.
• Finds Mistakes Early: With the help of a generic array, errors are detected while coding instead of during program execution.
• No Extra Conversions: With the help of a generic array, there is no need to manually change data types, making the code simpler.
• Easy to Manage: With the help of a generic array, the code becomes cleaner and easier to understand.

Disadvantages of Generic Arrays in Java

• Java does not allow direct creation of generic arrays; we have to create a class and use generic arrays.
• Generic arrays cannot store primitive data types like int, double, or char. You must use wrapper classes (Integer, Double, etc.).
• Generic arrays cannot be used in some cases, such as creating arrays of generic types inside other generic classes.

Conclusion

In this blog, we have learned about generic arrays in Java and different methods to create a generic array in Java such as Object arrays, Reflection, Collections, ArrayList, and Streams. You can use one of these methods according to your project requirements.

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