Closed
Description
child of #14890
Previously proposed in #6943
when using pattern matching with instance of, the null-check is redundant as instanceof operator implies non-nullity. It will be good if we have a check that violates this redundant condition to lead to a more concise and clear code
Config:
$ cat config.xml
<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
"-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
"https://checkstyle.org/dtds/configuration_1_3.dtd">
<module name="Checker">
<module name="TreeWalker">
<module name="UnnecessaryNullCheckWithInstanceof"/>
</module>
</module>Example 1
public class Test {
void test(Object obj) {
if (obj != null && obj instanceof String) { // violation
System.out.println("string");
}
}
}Expected Output
$ java -jar checkstyle-10.19.0-all.jar -c config.xml Test.java
Starting audit...
[ERROR] D:\Test.java:3:17: Unnecessary nullity check with instanceof operator in conditional expression.
Audit done.
Checkstyle ends with 1 errors.
the check should violate the null check here because Condition obj != null is covered by subsequent
condition obj instanceof String `
Example 2
class Test {
record ColoredPoint(int x, int y, String c) { }
void test(Object obj) {
if (obj instanceof ColoredPoint(_,_,_) && obj != null) { // violation
System.out.println("string");
}
}
}Expected Output
$ java -jar checkstyle-10.19.0-all.jar -c config.xml Test.java
Starting audit...
[ERROR] D:\Test.java:4:55: Unnecessary nullity check with instanceof operator in conditional expression.
Audit done.
Checkstyle ends with 1 errors.
the check should violate the null check here because Condition obj != null is always 'true' when reached