Basic Rules ("rulesets/basic.xml")

AssertWithinFinallyBlock

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

New in 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

New in 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

New in 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

New in 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.

For more information see these links:

Example of violations:

    Class.forName('SomeClassName')
    Class.forName(aClassName, true, aClassLoader)

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

DeadCode Rule

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

New in 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

New in 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 volations are produced. 'ignore

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, 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

New in 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

New in 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

New in 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.

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
        }
    }

EqualsOverloaded Rule

New in 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 {
        // Overloading equals() with 2 parameters is just mean
        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 }
    }

    @SuppressWarnings('EqualsOverloaded')
    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

New in 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

New in 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

New in 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

New in 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)
    Integer.getInteger(value, radix)

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

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

RandomDoubleCoercedToZero Rule

New in 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
        }
    }