Return an empty collection instead of null. Open
return null;
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Returning null
instead of an actual array or collection forces callers of the method to explicitly test for nullity, making them more
complex and less readable.
Moreover, in many cases, null
is used as a synonym for empty.
Noncompliant Code Example
public static List<Result> getResults() { return null; // Noncompliant } public static Result[] getResults() { return null; // Noncompliant } public static void main(String[] args) { Result[] results = getResults(); if (results != null) { // Nullity test required to prevent NPE for (Result result: results) { /* ... */ } } }
Compliant Solution
public static List<Result> getResults() { return Collections.emptyList(); // Compliant } public static Result[] getResults() { return new Result[0]; } public static void main(String[] args) { for (Result result: getResults()) { /* ... */ } }
See
- CERT, MSC19-C. - For functions that return an array, prefer returning an empty array over a null value
- CERT, MET55-J. - Return an empty array or collection instead of a null value for methods that return an array or collection
Return an empty collection instead of null. Open
return null;
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Returning null
instead of an actual array or collection forces callers of the method to explicitly test for nullity, making them more
complex and less readable.
Moreover, in many cases, null
is used as a synonym for empty.
Noncompliant Code Example
public static List<Result> getResults() { return null; // Noncompliant } public static Result[] getResults() { return null; // Noncompliant } public static void main(String[] args) { Result[] results = getResults(); if (results != null) { // Nullity test required to prevent NPE for (Result result: results) { /* ... */ } } }
Compliant Solution
public static List<Result> getResults() { return Collections.emptyList(); // Compliant } public static Result[] getResults() { return new Result[0]; } public static void main(String[] args) { for (Result result: getResults()) { /* ... */ } }
See
- CERT, MSC19-C. - For functions that return an array, prefer returning an empty array over a null value
- CERT, MET55-J. - Return an empty array or collection instead of a null value for methods that return an array or collection
Rename "stringResponse" which hides the field declared at line 14. Open
String stringResponse = this.stringResponse.toString();
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Overriding or shadowing a variable declared in an outer scope can strongly impact the readability, and therefore the maintainability, of a piece of code. Further, it could lead maintainers to introduce bugs because they think they're using one variable but are really using another.
Noncompliant Code Example
class Foo { public int myField; public void doSomething() { int myField = 0; ... } }
See
- CERT, DCL01-C. - Do not reuse variable names in subscopes
- CERT, DCL51-J. - Do not shadow or obscure identifiers in subscopes
All overloaded methods should be placed next to each other. Placing non-overloaded methods in between overloaded methods with the same type is a violation. Previous overloaded method located at line '128'. Open
public Map<String, Object> getHeaders() {
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Checks that overloaded methods are grouped together. Overloaded methods have the samename but different signatures where the signature can differ by the number of inputparameters or type of input parameters or both.
This documentation is written and maintained by the Checkstyle community and is covered under the same license as the Checkstyle project.