Groovy - Built-in Exceptions

Groovy extends several exception classes inside the standard package groovy.lang.

The most general of these exceptions are subclasses of the standard type RuntimeException. Since groovy.lang is implicitly imported into all Groovy programs, most exceptions derived from RuntimeException are automatically available.

Types of Built-in Exceptions

Built-in Exceptions in Groovy are categorized into two categories Checked Exceptions and Unchecked Exceptions.

• Checked Exceptions: The checked exceptions are handled by the programmer during writing the code, they can be handled using the try-catch block. These exceptions are checked at compile-time.
• Unchecked Exceptions: The unchecked exceptions are not handled by the programmer. These exceptions are thrown on run-time. Some of the unchecked exceptions are NullPointerException, ArrayIndexOutOfBoundsException, ArithmeticException, etc.

Common Built-in Exceptions in Groovy

Groovy inherits several other types of exceptions from Java that relate to its various class libraries. Following is the list of Groovy Unchecked and Checked RuntimeException.

Example - Demonstrating Arithmetic Exception Without try-catch

In this example, we're creating an error by dividing a value by 0. In this case, an unchecked exception will be raised. Being unchecked, compiler won't complain and program will compile successfully. Once program runs, the exception will be thrown and JVM will intercepts the same and terminate the program before printing the last statement.

Example.groovy

class Example {
   static void main(String[] args) {       
      int b = 0;
      int c = 1/b;
      println("c :" + c);
   }
}

Output

This will produce the following result−

Caught: java.lang.ArithmeticException: / by zero
java.lang.ArithmeticException: / by zero
	at Example.main(Example.groovy:4)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)

Example - Demonstrating Arithmetic Exception With try-catch

In this example, we're handling unchecked exception. As first step, we're generating an error by dividing a value by 0. In this case, an unchecked exception will be raised. We're handling via ArithmeticException. Once program runs, the exception will be thrown and catch block will intercepts the same and print the last statement.

Example.groovy

class Example {
   static void main(String[] args) {
      try {
         int b = 0;
         int c = 1/b;
         println("c :" + c);
      }
      catch (ArithmeticException e) {
         println("Exception thrown  :" + e);
      }
      println("Out of the block");
   }
}

Output

This will produce the following result−

Exception thrown  :java.lang.ArithmeticException: / by zero
Out of the block

Example - Demonstrating No Such Method Exception

In this example, we're showcasing that a checked exception is to be handled by code otherwise compiler will complain. Whenever a method throws a checked exception, it has to either handle the exception or declare throws exception statement as we're doing for getName() method. When we try to run the method, JVM complains the compilation problem as shown in output listed below:

Example.groovy

class Example {
   static void main(String[] args) {
      new Example().getName();
   }
   
   String getName() throws NoSuchMethodException {
	   throw new NoSuchMethodException();
   }
}

Output

This will produce the following result−

Caught: java.lang.NoSuchMethodException
java.lang.NoSuchMethodException
	at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:62)
at Example.getName(Example.groovy:7)
	at Example$getName.call(Unknown Source)
	at Example.main(Example.groovy:3)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)