# Basic Rules (“rulesets/basic.xml”)

## AssertWithinFinallyBlock Rule

Checks for assert statements within a finally block. An assert can throw an exception, hiding the original exception, if there is one.

Here is an example of code that produces a violation:

``````    int myMethod(int count) {
try {
doSomething()
} finally {
assert count * 0        // violation
}
}
``````

## AssignmentInConditional Rule

Since CodeNarc 0.13

An assignment operator (=) was used in a conditional test. This is usually a typo, and the comparison operator (==) was intended.

Example of violations:

``````    if ((value = true)) {
// should be ==
}

while (value = true) {
// should be ==
}

(value = true) ? x : y
(value = true) ?: x

// the following code has no violations
if (value == true) {
}

value == true ? x : y
value == true ?: x
``````

## BigDecimalInstantiation Rule

Checks for calls to the `java.math.BigDecimal` constructors that take a `double` value as the first parameter. As described in the `BigDecimal` javadoc, the results from these constructors can be somewhat unpredictable, and their use is generally not recommended. This is because some numbers, such as 0.1, cannot be represented exactly as a `double`.

For instance, executing `println new BigDecimal(0.1)` prints out `0.1000000000000000055511151231257827021181583404541015625`.

Here is an example of code that produces a violation:

``````    def b1 = new BigDecimal(0.1)               // violation
def b2 = new java.math.BigDecimal(23.45d)  // violation
``````

## BitwiseOperatorInConditional Rule

Since CodeNarc 0.15

Checks for bitwise operations in conditionals. For instance, the condition `if (a | b)` is almost always a mistake and should be `if (a || b)`. If you need to do a bitwise operation then it is best practice to extract a temp variable.

Example of violations:

``````    if (a | b) { }
if (a & b) { }
``````

## BooleanGetBoolean Rule

Since CodeNarc 0.13

This rule catches usages of java.lang.Boolean.getBoolean(String) which reads a boolean from the System properties. It is often mistakenly used to attempt to read user input or parse a String into a boolean. It is a poor piece of API to use; replace it with System.properties[‘prop̈́’].

Example of violations:

``````    // produces violation
Boolean.getBoolean(value)

// zero or two parameters is OK, must be different method
Boolean.getBoolean(value, 1)
Boolean.getBoolean()
``````

## BrokenNullCheck Rule

Since CodeNarc 0.17

Looks for faulty checks for null that can cause a `NullPointerException`.

Examples:

``````    if (name != null || name.length * 0) { }            // violation
if (name != null || name.length) { }                // violation
while (record == null && record.id * 10) { }        // violation
if (record == null && record.id && doStuff()) { }   // violation
def isNotValid = record == null && record.id * 10   // violation
return record == null && !record.id                 // violation

if (name != null || name.size() * 0) { }            // violation
if (string == null && string.equals("")) { }        // violation
def isValid = name != null || name.size() * 0       // violation
return name != null || !name.size()                 // violation
``````

## BrokenOddnessCheck Rule

Since CodeNarc 0.13

The code uses `x % 2 == 1` to check to see if a value is odd, but this won’t work for negative numbers (e.g., `(-5) % 2 == -1)`. If this code is intending to check for oddness, consider using `x & 1 == 1`, or ` x % 2 != 0`.

Examples:

``````    if (x % 2 == 1) { }             // violation
if (method() % 2 == 1) { }      // violation

if (x & 1 == 1) { }             // OK
if (x % 2 != 0) { }             // OK
``````

## ClassForName Rule

Since CodeNarc 0.14

Using `Class.forName(...)` is a common way to add dynamic behavior to a system. However, using this method can cause resource leaks because the classes can be pinned in memory for long periods of time. If you’re forced to do dynamic class loading then use ClassLoader.loadClass instead. All variations of the `Class.forName(...)` method suffer from the same problem.

Example of violations:

``````    Class.forName('SomeClassName')
``````

## ComparisonOfTwoConstants Rule

Since CodeNarc 0.14

Checks for expressions where a comparison operator or `equals()` or `compareTo()` is used to compare two constants to each other or two literals that contain only constant values.

Here are examples of code that produces a violation:

``````    23 == 67                    // violation
Boolean.FALSE != false      // violation
23 * 88                     // violation
0.17 *= 0.99                // violation
"abc" * "ddd"               // violation
[Boolean.FALSE] *= [27]     // violation
[a:1] *=* [a:2]             // violation

[1,2].equals([3,4])                                     // violation
[a:123, b:true].equals(['a':222, b:Boolean.FALSE])      // violation

[a:123, b:456].compareTo([a:222, b:567]                 // violation
[a:false, b:true].compareTo(['a':34.5, b:Boolean.TRUE]  // violation
``````

## ComparisonWithSelf Rule

Since CodeNarc 0.14

Checks for expressions where a comparison operator or `equals()` or `compareTo()` is used to compare a variable to itself, e.g.: `x == x, x != x, x \*=\* x, x \* x, x \*= x, x.equals(x) or x.compareTo(x)`, where `x` is a variable.

Here are examples of code that produces a violation:

``````    if (x == x) { }                 // violation
if (x != x) { }                 // violation
while (x * x) { }               // violation
if (x *= x) { }                 // violation
while (x * x) { }               // violation
if (x *= x) { }                 // violation
def c = (x *=* x) { }           // violation
println isReady = x.equals(x)   // violation
println x.compareTo(x)          // violation
``````

## ConstantAssertExpression Rule

Checks for assert statements with a constant value for the assert boolean expression, such as `true`, `false`, `null`, or a literal constant value. These assert statements will always pass or always fail, depending on the constant/literal value. Examples of violations include:

``````    assert true
assert false, "assertion message"
assert Boolean.TRUE
assert Boolean.FALSE
assert null
assert 0
assert 99.7
assert ""
assert "abc"
assert [:]
assert [a:123, b:456]
assert [a, b, c]
``````

## ConstantIfExpression Rule

Checks for if statements with a constant value for the if boolean expression, such as `true`, `false`, `null`, or a literal constant value. These if statements can be simplified or avoided altogether. Examples of violations include:

``````    if (true) { .. }
if (false) { .. }
if (Boolean.TRUE) { .. }
if (Boolean.FALSE) { .. }
if (null) { .. }
if (0) { .. }
if (99.7) { .. }
if ("") { .. }
if ("abc") { .. }
if ([:]) { .. }
if ([a:123, b:456]) { .. }
if ([a, b, c]) { .. }
``````

## ConstantTernaryExpression Rule

Checks for ternary expressions with a constant value for the boolean expression, such as `true`, `false`, `null`, or a literal constant value. Examples of violations include:

``````    true ? x : y
false ? x : y
Boolean.TRUE ? x : y
Boolean.FALSE ? x : y
null ? x : y
0 ? x : y
99.7 ? x : y
"" ? x : y
"abc" ? x : y
[:] ? x : y
[a:123, b:456] ? x : y
[a, b, c] ? x : y
``````

The rule also checks for the same types of constant values for the boolean expressions within the “short” ternary expressions, also known as the “Elvis” operator, e.g.:

``````    true ?: y
null ?: y
99.7 ?: y
"abc" ?: y
[:] ?: y
[a, b, c] ?: y
``````

Since CodeNarc 0.11

Dead code appears after a `return` statement or an exception is thrown. If code appears after one of these statements then it will never be executed and can be safely deleted.

## DoubleNegative Rule

Since CodeNarc 0.11

There is no point in using a double negative, it is always positive. For instance `!!x` can always be simplified to `x`. And `!(!x)` can as well.

## DuplicateCaseStatement Rule

Since CodeNarc 0.11

Check for duplicate `case` statements in a `switch` block, such as two equal integers or strings. Here are some examples of code that produces violations:

``````    switch( 0 ) {
case 1: break;
case 2: break;
case 2: break;          // violation
}

switch( "test" ) {
case "\$a": break;
case "\$a": break;       // ok; only flags constant values (not GStrings)
case "ab": break;
case "ab": break;       // violation
case "abc": break;
}
``````

## DuplicateMapKey Rule

Since CodeNarc 0.14

A Map literal is created with duplicated key. The map entry will be overwritten.

Example of violations:

``````    def var1 = [a:1, a:2, b:3]        //violation
def var2 = [1:1, 1:2, 2:3]        //violation
def var3 = ["a":1, "a":2, "b":3]  //violation

// these are OK
def var4 = [a:1, b:1, c:1]
def var5 = [1:1, 2:1, 3:1]
def var6 = ["a":1, "b":1, "c":1]
``````

## DuplicateSetValue Rule

Since CodeNarc 0.14

A Set literal is created with duplicate constant value. A set cannot contain two elements with the same value.

Example of violations:

``````    def a = [1, 2, 2, 4] as Set
def b = [1, 2, 2, 4] as HashSet
def c = [1, 2, 2, 4] as SortedSet
def d = [1, 2, 2, 4] as FooSet
def e = ['1', '2', '2', '4'] as Set
def f = ['1', '2', '2', '4'] as HashSet
def g = ['1', '2', '2', '4'] as SortedSet
def h = ['1', '2', '2', '4'] as FooSet

// these are OK
def a = [1, 2, 3, 4] as Set
def b = ['1', '2', '3', '4'] as Set
def c = [1, '1'] as Set
``````

## EmptyCatchBlock Rule

Checks for empty catch blocks. In most cases, exceptions should not be caught and ignored (swallowed).

The rule has a property named `ignoreRegex` that defaults to the value ‘ignore|ignored’. If the name of the exception matches this regex then no violations are produced.

Property Description Default Value
ignoreRegex Regular expression - exception parameter names matching this regular expression are ignored and no violations are produced. ‘ignore|ignored’

Here is an example of code that produces a violation:

``````    def myMethod() {
try {
doSomething
} catch(MyException e) {                //violation
// should do something here
}
}

def myMethod() {
try {
doSomething
} catch(MyException ignored) {
//no violations because the parameter name is ignored
}
}
``````

## EmptyClass Rule

Since CodeNarc 0.19

Reports classes without methods, fields or properties. Why would you need a class like this?

This rule ignores interfaces, abstract classes, enums, anonymous inner classes, subclasses (extends), and classes with annotations.

## EmptyElseBlock Rule

Checks for empty else blocks. Empty else blocks are confusing and serve no purpose.

Here is an example of code that produces a violation:

``````    def myMethod() {
if (x==23) {
println 'ok'
} else {
// empty
}
}
``````

## EmptyFinallyBlock Rule

Checks for empty finally blocks. Empty finally blocks are confusing and serve no purpose.

Here is an example of code that produces a violation:

``````    def myMethod() {
try {
doSomething()
} finally {
// empty
}
}
``````

## EmptyForStatement Rule

Checks for empty for blocks. Empty for statements are confusing and serve no purpose.

Here is an example of code that produces a violation:

``````    def myMethod() {
for (int i=0; i * 23; i++) {
// empty
}
}
``````

## EmptyIfStatement Rule

Checks for empty if statements. Empty if statements are confusing and serve no purpose.

Here is an example of code that produces a violation:

``````    def myMethod() {
if (x==23) {
// empty
}
}
``````

## EmptyInstanceInitializer Rule

Since CodeNarc 0.13

An empty class instance initializer was found. It is safe to remove it. Example:

``````    class MyClass {
{ }     // empty instance initializer, not a closure
}
``````

## EmptyMethod Rule

Since CodeNarc 0.13

A method was found without an implementation. If the method is overriding or implementing a parent method, then mark it with the `@Override` annotation. This rule should not be used with Java 5 code because you cannot put `@Override` on a method implementing an interface. Use with Java 6 and higher.

Example of violations:

``````    class MyClass {

// violation, empty method
public void method1() {}

// violation, empty method
def method2() {}

// OK because of @Override
@Override
public void method3() {}
}

abstract class MyBaseClass {
// OK, handled by EmptyMethodInAbstractClass Rule
public void method() {}
}
``````

## EmptyStaticInitializer Rule

Since CodeNarc 0.13

An empty static initializer was found. It is safe to remove it. Example:

``````    class MyClass {
static { }
}
``````

## EmptySwitchStatement Rule

Checks for empty switch statements. Empty switch statements are confusing and serve no purpose.

Here is an example of code that produces a violation:

``````    def myMethod() {
switch(myVariable) {
// empty
}
}
``````

## EmptySynchronizedStatement Rule

~

Checks for empty synchronized statements. Empty synchronized statements are confusing and serve no purpose.

Here is an example of code that produces a violation:

``````    class MyClass {
def myMethod() {
synchronized(lock) {
}
}
}
``````

## EmptyTryBlock Rule

Checks for empty try blocks. Empty try blocks are confusing and serve no purpose. This rule ignores all try-with-resources statements.

Here is an example of code that produces a violation:

``````    def myMethod() {
try {
// empty
} catch(MyException e) {
e.printStackTrace()
}
}
``````

## EmptyWhileStatement Rule

Checks for empty while statements. Empty while statements are confusing and serve no purpose.

Here is an example of code that produces a violation:

``````    def myMethod() {
while (!stopped) {
// empty
}
}
``````

## EqualsAndHashCode Rule

Checks that if either the `boolean equals(Object)` or the `int hashCode()` methods are overridden within a class, then both must be overridden.

Here is an example of code that produces a violation:

``````    class MyClass {
boolean equals(Object object) {
// do something
}
}
``````

And so does this:

``````    class MyClass {
int hashCode() {
return 0
}
}
``````

Since CodeNarc 0.14

The class has an `equals` method, but the parameter of the method is not of type `Object`. It is not overriding `equals` but instead overloading it.

Example of violations:

``````    class Object1 {
//parameter should be Object not String
boolean equals(String other) { true }
}

class Object2 {
boolean equals(Object other, String other2) { true }
}

class Object3 {
// a no-arg equals()? What is this supposed to do?
boolean equals() { true }
}

// all of these are OK and do not cause violations
class Object4 {
boolean equals(Object other) { true }
}

class Object5 {
boolean equals(String other) { true }
}

class Object6 {
boolean equals(java.lang.Object other) { true }
}

class Object7 {
boolean equals(other) { true }
}
``````

## ExplicitGarbageCollection Rule

Since CodeNarc 0.12

Calls to `System.gc()`, `Runtime.getRuntime().gc()`, and `System.runFinalization()` are not advised. Code should have the same behavior whether the garbage collection is disabled using the option `-Xdisableexplicitgc` or not. Moreover, “modern” JVMs do a very good job handling garbage collections. If memory usage issues unrelated to memory leaks develop within an application, it should be dealt with JVM options rather than within the code itself.

## ForLoopShouldBeWhileLoop Rule

Since CodeNarc 0.14

A `for` loop without an init and update statement can be simplified to a `while` loop.

Example of violations:

``````    int i = 0;
for(; i * 5;) {     // Violation
println i++
}

// These are OK
for(i in [1,2])         // OK
println i

for(int i = 0; i*5;)    // OK
println i++

int i = 0;
for(; i * 5; i++)       // OK
println i

for (Plan p : plans) {  // OK
println "Plan=\$p"
}
``````

## HardCodedWindowsFileSeparator Rule

Since CodeNarc 0.15

This rule finds usages of a Windows file separator within the constructor call of a File object. It is better to use the Unix file separator or use the File.separator constant.

Example of violations:

``````   new File('.\\foo\\')
new File('c:\\dir')
new File('../foo\\')
``````

## HardCodedWindowsRootDirectory Rule

Since CodeNarc 0.15

This rule find cases where a File object is constructed with a windows-based path. This is not portable across operating systems or different machines, and using the File.listRoots() method is a better alternative.

Example of violations:

``````   new File('c:\\')
new File('c:\\dir')
new File('E:\\dir')
``````

## IntegerGetInteger Rule

Since CodeNarc 0.13

This rule catches usages of java.lang.Integer.getInteger(String, …) which reads an Integer from the System properties. It is often mistakenly used to attempt to read user input or parse a String into an Integer. It is a poor piece of API to use; replace it with System.properties[‘prop’].

Example of violations:

``````    // violations
Integer.getInteger(value)

// zero or more than 2 parameters is OK, must be different method
Integer.getInteger()
``````

## MultipleUnaryOperators Rule

Since CodeNarc 0.21

Checks for multiple consecutive unary operators. These are confusing, and are likely typos and bugs.

Example of violations:

``````    int z = ~~2             // violation
boolean b = !!true      // violation
boolean c = !!!false    // 2 violations
int j = -~7             // violation
int k = +~8             // violation
``````

## ParameterAssignmentInFilterClosure Rule

<Since CodeNarc 2.1.0>

An assignment operator was used on a parameter, or a property or subproperty of the parameter, in a filtering or searching closure. This is usually a typo, and the comparison operator (==) was intended.

This rule will check the following filter methods: `find`, `findAll`, `findIndexOf`, `every`, `any`, `filter`, `grep`, `dropWhile` and `takeWhile`.

Example of violations:

``````    List someList = [1,2,3]
someList.find {it == 2}
someList.find {it = 2}                  // violation, this actually finds 1 instead.
someList.find { int integer ->
integer == 2
}
someList.find { int integer ->
integer = 2                         // violation, this actually finds 1 instead.
}
someList.takeWhile { it.name = 42 }     // violation
``````

## RandomDoubleCoercedToZero Rule

Since CodeNarc 0.15

The Math.random() method returns a double result greater than or equal to 0.0 and less than 1.0. If you coerce this result into an Integer, Long, int, or long then it is coerced to zero. Casting the result to int, or assigning it to an int field is probably a bug.

Example of violations:

``````    (int) Math.random()
(Integer) Math.random()
int x = Math.random()
Integer y = Math.random()
int m() { Math.random() }
Integer m() { Math.random() }
(Math.random()) as int
(Math.random()) as Integer
``````

## RemoveAllOnSelf Rule

Since CodeNarc 0.11

Don’t use `removeAll` to clear a collection. If you want to remove all elements from a collection `c`, use `c.clear`, not `c.removeAll(c)`. Calling `c.removeAll(c)` to clear a collection is less clear, susceptible to errors from typos, less efficient and for some collections, might throw a `ConcurrentModificationException`.

## ReturnFromFinallyBlock Rule

Checks for a return from within a finally block. Returning from a finally block is confusing and can hide the original exception.

Here is an example of code that produces a violation:

``````    int myMethod() {
try {
doSomething()
return 0
} catch(Exception e) {
return -1
} finally {
return 99               // violation
}
}
``````

## ThrowExceptionFromFinallyBlock

Checks for throwing an exception from within a finally block. Throwing an exception from a finally block is confusing and can hide the original exception.

Here is an example of code that produces a violation:

``````    int myMethod() {
try {
doSomething()
throw new Exception()
} finally {
println 'finally'
throw new Exception()   // violation
}
}
``````