Java - InstantiationException

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The InstantiationException in Java occurs when an application attempts to create an instance of a class using the newInstance() method of the Class class, but the class cannot be instantiated because it is either an interface or an abstract class. This is a checked exception.

Following is the reason when JVM throws an InstantiationException in Java:

• Occurs when an application attempts to create an instance of a class using the newInstance() method of the Class class, but the class cannot be instantiated because it is either an interface or an abstract class.

Constructors of InstantiationException

There are two constructors of InstantiationException class:

• InstantiationException(): This constructor is used to create an InstantiationException object without any message.
• InstantiationException(String message): This constructor is used to create an InstantiationException object with a message.

Methods of InstantiationException

There are some methods of InstantiationException class:

Method	Description
getMessage()	It is used to return the message of the exception.
toString()	It is used to return the detail message string of the exception.
printStackTrace()	It is used to print the stack trace of the exception.

Example of InstantiationException

In this example, we are trying to create an instance of an interface using the newInstance() method of the Class class, so JVM will throw an InstantiationException.

import java.util.ArrayList;

public class InstantiationExceptionExample {

   public static void main(String[] args) {
      Class<ArrayList> c = ArrayList.class;
      try {
         ArrayList<Integer> list = c.newInstance();
      } catch (InstantiationException e) {
         e.printStackTrace();
      } catch (IllegalAccessException e) {
         e.printStackTrace();
      }
   }
}

Output

Following is the output of the above code:

java.lang.InstantiationException: java.util.ArrayList
    at java.base/jdk.internal.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:48)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490)
    at InstantiationExceptionExample.main(InstantiationExceptionExample.java:7)

Handling InstantiationException

In this example, we are trying to create an instance of an interface using the newInstance() method of the Class class, so JVM will throw an InstantiationException. We are handling this exception using try-catch block.

import java.util.ArrayList;

public class InstantiationExceptionExample {

   public static void main(String[] args) {
      Class<ArrayList> c = ArrayList.class;
      try {
         ArrayList<Integer> list = c.newInstance();
      } catch (InstantiationException e) {
         System.out.println("InstantiationException: " + e.getMessage());
      } catch (IllegalAccessException e) {
         System.out.println("IllegalAccessException: " + e.getMessage());
      }
   }
}

Output

Following is the output of the above code:

InstantiationException: java.util.ArrayList

As you can see in the output, JVM throws an InstantiationException because we are trying to create an instance of an interface using the newInstance() method of the Class class.

Fixing the InstantiationException using reflection

Another method to fix the InstantiationException is to use the getDeclaredConstructor() method of the Class class to get the constructor of the class and then use the newInstance() method of the Constructor class to create an instance of the class.

import java.util.ArrayList;
import java.lang.reflect.Constructor;

public class InstantiationExceptionExample {

   public static void main(String[] args) {
      Class<ArrayList> c = ArrayList.class;
      try {
         Constructor<ArrayList> constructor = c.getDeclaredConstructor();
         constructor.setAccessible(true);
         ArrayList<Integer> list = constructor.newInstance();
         System.out.println("executed successfully");
      } catch (Exception e) {
         e.printStackTrace();
      }
   }
}

Output

Following is the output of the above code:

executed successfully

As you can see in the output, we are creating an instance of the ArrayList class using reflection and it is executed successfully.

How to avoid InstantiationException?

Following are the ways to avoid InstantiationException:

• Always check the class before creating an instance of it.
• Always use the getDeclaredConstructor() method of the Class class to get the constructor of the class.
• Always use the newInstance() method of the Constructor class to create an instance of the class.

By following the above ways, you can avoid the InstantiationException in Java.