Home » Core Java » reflection » java.lang.reflect.Array Example

About Theodora Fragkouli

Theodora Fragkouli
Theodora has graduated from Computer Engineering and Informatics Department in the University of Patras. She also holds a Master degree in Economics from the National and Technical University of Athens. During her studies she has been involved with a large number of projects ranging from programming and software engineering to telecommunications, hardware design and analysis. She works as a junior Software Engineer in the telecommunications sector where she is mainly involved with projects based on Java and Big Data technologies.

java.lang.reflect.Array Example

In this example we shall explain how to use java.lang.reflect.Array. The java.lang.reflect.Array class provides static methods to dynamically create and access Java arrays. Arrays are objects that contain values of the same type, with immutable length. So, an array’s components of the same type and their number is always fixed. The length of an array must be set when an array is created, whereas the type of the components may be primitive (int, byte, long), an object type (String, Integer, Long), or even another array, but is always single.

Below, we make use of the methods provided in the java.lang.reflect.Array class, in order to create new instances of arrays, set values to their components, get their components values, get the types of the components of every array and finally get each array’s length.

    Create an Array

  • We create a new instance of an array, of any of the types mentioned above, using the newInstance(Class componentType, int... dimensions) (when we want to set many dimensions), or newInstance(Class componentType, int length) (when we only want to set the array number of components) methods of java.lang.reflect.Array.
  • Access an array’s components

  • In order to set the value of the indexed component of an array, we use the set(Object array, int index, Object value) or set...(Object array, int index, ... value) API methods of java.lang.reflect.Array.
  • In order to get the value of the indexed component of an array, we use the get(Object array, int index) or get...(Object array, int index) API methods of java.lang.reflect.Array.
  • Obtain the type of an array’s components

  • In order to get the type of the array’s components, we first get the Class of the array, making use of getClass() API method of Object, and then we use the getComponentType() method of Class. Note that all components in an array are of the same type.
  • Get the number of an array’s components

  • In order to get an array’s length we use the getLength(Object array) API method of java.lang.reflect.Array. Note that the array’s length is fixed and must be set in initialization of an array.

Always note that an ArrayIndexOutOfBoundsException may occur, when trying to access a specified index which is negative, greater than or equal to the length of the specified array.

ArrayExample.java

package com.javacodegeeks.snippets.core;

import java.lang.reflect.Array;

public class ArrayExample {

	private static String[] strArr = (String[]) Array.newInstance(String.class, 10);
	private static int[] intArr = (int[]) Array.newInstance(int.class, 10);
	
	public static void fillArrays() {
		for(int i=0; i<=9; i++){
			Array.set(strArr, i, String.valueOf(i));
			Array.setInt(intArr, i, i);
		}
	}
	
	public static void showArrays() {
		System.out.println("-Arrays have: ");
		for(int i=0; i<=9; i++){
			System.out.println("At position " + i + " strArr component is :" + Array.get(strArr, i));
			System.out.println("At position " + i + " intArr component is :" + Array.getInt(intArr, i));
		}
	}
		
	public static void main(String[] args) {
		fillArrays();
		showArrays();
		System.out.println("Components of the strArr are of type : " + strArr.getClass().getComponentType());
		System.out.println("Length of the strArr is : " + Array.getLength(strArr));
		System.out.println("Components of the intArr are of type : " + intArr.getClass().getComponentType());
		System.out.println("Length of the intArr is : " + Array.getLength(strArr));
	}
}

If you run the example above, you will get the result below:

Output

-Arrays have: 
At position 0 strArr component is :0
At position 0 intArr component is :0
At position 1 strArr component is :1
At position 1 intArr component is :1
At position 2 strArr component is :2
At position 2 intArr component is :2
At position 3 strArr component is :3
At position 3 intArr component is :3
At position 4 strArr component is :4
At position 4 intArr component is :4
At position 5 strArr component is :5
At position 5 intArr component is :5
At position 6 strArr component is :6
At position 6 intArr component is :6
At position 7 strArr component is :7
At position 7 intArr component is :7
At position 8 strArr component is :8
At position 8 intArr component is :8
At position 9 strArr component is :9
At position 9 intArr component is :9
Components of the strArr are of type : class java.lang.String
Length of the strArr is : 10
Components of the intArr are of type : class int
Length of the intArr is : 10

 

Download the Eclipse Project

This was an example of java.lang.reflect.Array.

Download
You can download the full source code of this example here: java.lang.reflect.ArrayExample
(No Ratings Yet)
Start the discussion Views Tweet it!

Do you want to know how to develop your skillset to become a Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you our best selling eBooks for FREE!

 

1. JPA Mini Book

2. JVM Troubleshooting Guide

3. JUnit Tutorial for Unit Testing

4. Java Annotations Tutorial

5. Java Interview Questions

6. Spring Interview Questions

7. Android UI Design

 

and many more ....

 

Receive Java & Developer job alerts in your Area

 

Leave a Reply

avatar
  Subscribe  
Notify of