Java - NoSuchMethodException

---

---

The Java NoSuchMethodException is thrown when a particular method is not found in a class. The NoSuchMethodException is a checked exception that is thrown when a particular method is not found in a class.

It extends ReflectiveOperationException, which is the superclass for exceptions thrown by reflection-related operations.

Hierarchy of NoSuchMethodException

Given below is the class hierarchy of NoSuchMethodException:

java.lang.Object
  ↳ java.lang.Throwable
      ↳ java.lang.Exception
          ↳ java.lang.ReflectiveOperationException
              ↳ java.lang.NoSuchMethodException

So, it means ReflectiveOperationException is the superclass for exceptions thrown by reflection-related operations and it is unchecked.

Cause of NoSuchMethodException

Following are the reasons when JVM throws a NoSuchMethodException in Java:

• A method that does not exist is accessed via reflection.
• A method exists but is private and is accessed using getMethod() instead of getDeclaredMethod().
• A misspelled method name is used.
• The class being inspected is dynamically loaded but does not contain the expected method.

Constructors of NoSuchMethodException

There are two constructors of NoSuchMethodException class:

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

Methods of NoSuchMethodException

There are some methods of NoSuchMethodException 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 1 : Accessing a Non-Existent Method

In this example, we are accessing a method that does not exist in the class, so JVM will throw a NoSuchMethodException.

import java.lang.reflect.Method;

public class NoSuchMethodExample {
   public static void main(String[] args) {
      Class<?> clazz = Class.forName("java.lang.String");
      Method method = clazz.getMethod("nonExistentMethod"); // This method does not exist
   }
}

Output

Following is the output of the above code:

NoSuchMethodExample.java:6: error: unreported exception NoSuchMethodException; must be caught or declared to be thrown
      Method method = clazz.getMethod("nonExistentMethod"); // This method does not exist
                                ^
2 errors

As you can see in the output, JVM throws a NoSuchMethodException because we are accessing a method that does not exist in the class.

Difference Between getMethod() and getDeclaredMethod()

There are two methods in the java.lang.Class class that are used to get the method of a class:

• getMethod(String name, Class<?>... parameterTypes): This method is used to get the public method of the class.
• getDeclaredMethod(String name, Class<?>... parameterTypes): This method is used to get the method of the class.

Following table shows the difference between getMethod() and getDeclaredMethod() methods:

Method	Visibility	Accesses Inherited Methods?
getMethod(String name, Class<?>... parameterTypes)	Only public	Yes
getDeclaredMethod(String name, Class<?>... parameterTypes)	Any (private, protected, public)	No

Example 2 : Accessing a Private Method Correctly

In this example, we are accessing a private method using getDeclaredMethod() method, so JVM will not throw a NoSuchMethodException.

import java.lang.reflect.Method;

public class NoSuchMethodExample {
   public static void main(String[] args) {
      Class<?> clazz = Class.forName("java.lang.String");
      Method method = clazz.getDeclaredMethod("nonExistentMethod"); // This method does not exist
   }
}

Output

Following is the output of the above code:

NoSuchMethodExample.java:6: error: unreported exception NoSuchMethodException; must be caught or declared to be thrown
      Method method = clazz.getDeclaredMethod("nonExistentMethod"); // This method does not exist
                                     ^
2 errors

As you can see in the output, JVM throws a NoSuchMethodException because we are accessing a method that does not exist in the class.

Handling NoSuchMethodException

In this example, we are accessing a method that does not exist in the class, so JVM will throw a NoSuchMethodException. We are handling this exception using a try-catch block.

import java.lang.reflect.Method;

public class NoSuchMethodExample {
   public static void main(String[] args) {
      try {
         Class<?> clazz = Class.forName("java.lang.String");
         Method method = clazz.getMethod("nonExistentMethod"); // This method does not exist
      } catch (NoSuchMethodException e) {
         System.out.println("Method does not exist");
      }
   }
}

Output

Following is the output of the above code:

Method does not exist

How to avoid NoSuchMethodException?

To avoid a NoSuchMethodException, you should always access the method of a class that exists in the class.

Let's try to access a method that exists in the class:

import java.lang.reflect.Method;

public class NoSuchMethodExample {
   public static void main(String[] args) {
      try {
         Class<?> clazz = Class.forName("java.lang.String");
         Method method = clazz.getMethod("length"); // This method exists
         System.out.println("Method exists");
      } catch (NoSuchMethodException e) {
         System.out.println("Method does not exist");
      }
   }
}

Output

Following is the output of the above code:

Method exists

As you can see in the output, we are accessing a method that exists in the class, so JVM does not throw a NoSuchMethodException.

Summary

• The NoSuchMethodException in Java occurs when a particular method is not found in a class.
• Following are the reasons when JVM throws a NoSuchMethodException in Java:
  • A method that does not exist is accessed via reflection.
  • A method exists but is private and is accessed using getMethod() instead of getDeclaredMethod().
  • A misspelled method name is used.
  • The class being inspected is dynamically loaded but does not contain the expected method.