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How to access MetaData Of a class using Java?

In this article, we are going to learn that how can we access metadata of a class using java? MetaData of a class includes the class name, fields name, methods, constructor etc. By Jyoti Singh Last updated : March 23, 2024

Access MetaData of a Java Class

To get the MetaData, we use Java reflection API. Java refractor class provides the methods to get the metadata of a class.

Methods to Access MetaData of a Java Class

Here, we are going to use the following methods:

1. class.forName()
   This method loads a class which is provided as the parameter , if class is not found it will throw an error.
2. isInterface()
   This function checks whether a class is an interface or not and returns a Boolean value.
3. getDeclaredFields()
   This returns all fields name of a class.
4. getDeclaredMethods()
   This returns all methods name of a class.
5. getDeclaredConstructor()
   This returns all constructor name of a class.

Java Program to Access MetaData of a Java Class

Let's understand them more clearly by this example. Here, we have a class name Product with three fields in it and an interface named NoteBook.

package logicProgramming;
/*
 * In This Program We are Going to Get Meta Data Of Running Class
 * And Going To Examine And Change The Behavior Of Class
 */
import java.lang.Class;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

//an interface 
interface NoteBook {
  int bookId = 100;
}

//a class 
class Product {
  private int productId;
  private String name;
  public long price;

  //constructor
  public Product(int productId, String name, long price) {
    this.productId = productId;
    this.name = name;
    this.price = price;
  }
  //constructor
  public Product() {}

  //this function prints the data of the object
  public void putProduct() {
    System.out.println("ProductId :" + this.productId + "\nName :" + this.name + "\nPrice" + this.price);
  }

  public String toString() {
    return ("ProductId :" + this.productId + "\nName :" + this.name + "\nPrice" + this.price);
    // to return object so that object values are printed rather 
    //than it's hexadecimal address
  }
}

//main class
public class ExClassMetaData_ReflectionAPI_JAVA {
  public static void main(String arg[]) {
    try {
      //Class.forName(ClassName)    Use For Loading The Class		
      Class cs = Class.forName("logicProgramming.Product");
      System.out.println(cs.getName()); //getName() function is getting the name of the class 

      //getClass()	 Is also used To get The meta Data Of Class
      System.out.println();
      Product P = new Product();
      Class pcls = P.getClass(); //getting the meta data of Product class
      System.out.println(pcls.getName());
      System.out.println();

      //public boolean isInterface()   tells that whether 
      //the current class is Interface or a Simple Class
      System.out.println(Class.forName("logicProgramming.Product").isInterface());

      //Book Is a Interface so It Will print True...	
      System.out.println();
      System.out.println(Class.forName("logicProgramming.NoteBook").isInterface());

      //public Field[] getDeclaredFields()	
      //returns an array of name of all fields of this class.	
      Field fields[] = cs.getDeclaredFields();
      System.out.println();
      System.out.println("Fields Of product Class");

      //loop to print the fields name of the class 
      for (int i = 0; i < fields.length; i++) {
        System.out.println(fields[i]);
      }

      //public Method[] getDeclaredMethods()	
      //returns an array of name of all methods of this class.    
      Method methods[] = pcls.getDeclaredMethods();
      System.out.println();
      System.out.println("Methods Of product Class");

      //loop to print the methods name of the class 
      for (int i = 0; i < methods.length; i++) {
        System.out.println(methods[i]);
      }

      //public Constructor[] getDeclaredConstructors()	
      //returns the total number of constructors of this class.
      Constructor < Product > constructors[] = pcls.getDeclaredConstructors();
      System.out.println();
      System.out.println("Constructors Of product Class");

      //loop to print the constructor name of the class 
      for (int i = 0; i < constructors.length; i++) {
        System.out.println(constructors[i]);
      }
    } catch (ClassNotFoundException e) {
      System.out.println(e);
    }
  }
}

Output

Here, we have all the meta data of the class.

Note: "logicProgramming" is the name of the package , replace it with your package name