ThrowsCount
Since Checkstyle 3.2
Description
Rationale: Exceptions form part of a method's interface. Declaring a
method to throw too many differently rooted exceptions makes
exception handling onerous and leads to poor programming practices
such as writing code like catch(Exception ex).
4 is the empirical value which is based on reports that we had for
the ThrowsCountCheck over big projects such as OpenJDK.
This check also forces developers to put exceptions into a hierarchy
such that in the simplest case, only one type of exception need be
checked for by a caller but any subclasses can be caught specifically
if necessary. For more information on rules for the exceptions and
their issues, see Effective Java: Programming Language Guide
Second Edition by Joshua Bloch pages 264-273.
ignorePrivateMethods - allows to skip private methods as they do not cause problems for other classes.
Properties
Examples
To configure check:
<module name="Checker">
<module name="TreeWalker">
<module name="ThrowsCount"/>
</module>
</module>
Example:
public class Example1 {
// violation below, 'Throws count is 5 (max allowed is 4)'
public void myFunction() throws CloneNotSupportedException,
ArrayIndexOutOfBoundsException,
StringIndexOutOfBoundsException,
IllegalStateException,
NullPointerException {
}
public void myFunc() throws ArithmeticException,
NumberFormatException,
NullPointerException {
}
private void privateFunc() throws CloneNotSupportedException,
ClassNotFoundException,
IllegalAccessException,
ArithmeticException,
ClassCastException {
}
private void func() throws IllegalStateException,
NullPointerException {
}
}
To configure the check so that it doesn't allow more than two throws per method:
<module name="Checker">
<module name="TreeWalker">
<module name="ThrowsCount">
<property name="max" value="2"/>
</module>
</module>
</module>
Example:
public class Example2 {
// violation below, 'Throws count is 5 (max allowed is 2)'
public void myFunction() throws CloneNotSupportedException,
ArrayIndexOutOfBoundsException,
StringIndexOutOfBoundsException,
IllegalStateException,
NullPointerException {
}
// violation below, 'Throws count is 3 (max allowed is 2)'
public void myFunc() throws ArithmeticException,
NumberFormatException,
NullPointerException {
}
private void privateFunc() throws CloneNotSupportedException,
ClassNotFoundException,
IllegalAccessException,
ArithmeticException,
ClassCastException {
}
private void func() throws IllegalStateException,
NullPointerException {
}
}
To configure the check so that it doesn't skip private methods:
<module name="Checker">
<module name="TreeWalker">
<module name="ThrowsCount">
<property name="ignorePrivateMethods" value="false"/>
</module>
</module>
</module>
Example:
public class Example3 {
// violation below, 'Throws count is 5 (max allowed is 4)'
public void myFunction() throws CloneNotSupportedException,
ArrayIndexOutOfBoundsException,
StringIndexOutOfBoundsException,
IllegalStateException,
NullPointerException {
}
public void myFunc() throws ArithmeticException,
NumberFormatException,
NullPointerException {
}
// violation below, 'Throws count is 5 (max allowed is 4)'
private void privateFunc() throws CloneNotSupportedException,
ClassNotFoundException,
IllegalAccessException,
ArithmeticException,
ClassCastException {
}
private void func() throws IllegalStateException,
NullPointerException {
}
}
Example of Usage
Violation Messages
All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.
Package
com.puppycrawl.tools.checkstyle.checks.design