Rules

This is a list of all the rules that are currently implemented in jSparrow.

Tags

Coding Conventions, Formatting, Free, Java 1.1, Java 1.2, Java 1.3, Java 1.4, Java 1.5, Java 1.8, Java 10, Java 5, Java 6, Java 7, Java 8, Java 9, Lambda, Logging, Loop, Old Language Constructs, Performance, Readability, String Manipulation

Free rules in jSparrow Starter

The following rules are included in jSparrow Starter. See the documentation at: Registration for 15 free rules.

Rule Name
1 Remove Double Negations
2 Replace Expression Lambda with Method Reference
3 Replace Equality Check with isEmpty()
4 Reorder String Equality Check
5 Organize Imports
6 Remove Unnecessary Thrown Exceptions on Method Signatures
7 Remove Boxing for String Conversions
8 Remove toString() on String
9 Remove Unnecessary Semicolons
10 Replace For-Loop with Enhanced-For-Loop
11 Replace Inefficient Constructors with valueOf()
12 Replace equals() on Enum Constants
13 Split Multiple Variable Declarations
14 Use @Override Annotation
15 Use Try-With-Resource

Summary

Use @Override Annotation

This rule adds the '@Override' annotation to methods overriding or implementing parent class methods.

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Replace Assignment with Compound Operator

Simplifies arithmetic operations that an compound operator where possible.

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Reorder String Equality Check

Moves the string literals in the left-hand-side of 'equals()' or 'equalsIgnoreCase()' when checking for equality.

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Reformat Code

Reformats code according to the coding conventions defined in Eclipse.

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Collapse If Statements

Collapses, when possible, the nested if-statements into a single one by concatenating the conditions with the infix operator &&.

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Remove Lambda Expression Braces

If the body of the lambda statement contains only a single expression, the braces are optional. It can be reduced to a lambda expression. This is comparable to if-statements or loops with a single expression inside their body, where braces are also optional.

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Remove Deprecated Date Constructs

Some 'java.util.Date' constructors like 'new Date(int year, int month, int day)', 'new Date(int year, int month, int date, int hrs, int min)' and 'new Date(int year, int month, int date, int hrs, int min, int sec)' are deprecated. A 'Calendar' instance should be used instead. This rule searches for deprecated date constructors, introduces calendar instances, sets the time corresponding to the parameters in the deprecated constructor, and replaces the latter with an invocation of 'Calendar.getTime()'.

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Make SerialVersionUID Static Final

Adds the modifiers static and final to SerialVersionUid long variables when they are absent.

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Remove Explicit Type Argument

Since Java 1.7 the Diamond Operator (<>) can be used to simplify instance creation where generics are involved.

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Reorder Modifiers

This rule reorders the modifiers on Type, Field and Method declarations.

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Remove Unused Parameters in Private Methods

Finds and removes unused parameters in private method declarations. Updates the affected method invocations accordingly.

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Remove Unnecessary Thrown Exceptions on Method Signatures

Removes the RuntimeExceptions, duplications and exceptions which are subtypes of already thrown exceptions on the method signatures.

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Remove toString() on String

Removes all invocations of 'toString()' method used on a 'String' element.

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Remove Null-Checks Before Instanceof

Finds and removes null-checks before occurrences of instanceof. Since null is not an instance of anything, the null-check is redundant.

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Remove Modifiers in Interface Properties

Removes the 'public' modifiers from method declarations and 'public static final' modifiers from field declarations in Java interfaces.

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Rename Fields

Renames the non-final fields to comply with the naming convention "^[a-z][a-zA-Z0-9]*$" i.e. a lower case prefix followed by any sequence of alpha-numeric characters

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Remove Explicit Call To super()

Removes unnecessary explicit call to the default constructor of the super class.

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Remove Unnecessary Semicolons

Removes the unnecessary semicolons from the code blocks.

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Remove Double Negations

Removes multiple negations from boolean expressions.

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Rearrange Class Members

This rule rearranges the body declarations of a class based on the Oracle Code Convention for File Organization.

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Remove Inherited Interfaces from Class Declaration

This rule removes interfaces from class declaration, which are already implemented by a super class. These interfaces are inherited from the super class.

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Remove Boxing for String Conversions

When calling 'toString()' on a boxed primitive no new instance of that primitive has to be created. This rule replaces occurrences of such code with a static method

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Add Braces to Control Statements

Checks if braces are used to encapsulate control statements and adds them if they aren't present.

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Insert Break Statements in For-loops

Finds the Enhanced For-loops whose sole purpose is to compute a boolean value without causing side effects and inserts a break statement immediately after the boolean value is computed. Thus, eliminating redundant loop iterations.

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Organize Imports

Organize Imports according to the Eclipse's built in Organize Imports functionality.

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Replace For-Loop with Stream::sum

Transforms enhanced for-loops which are only used for summing up the elements of a collection to a 'Stream::sum' invocation.

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Replace Expression Lambda with Method Reference

This rule simplifies expression lambdas by using method reference. The rule can only be applied if the parameters of the lambda expression and the method match.

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Replace Equality Check with isEmpty()

This rule replaces comparisons of 'length()' or 'size()' with 0 with a call to 'isEmpty()'. Any occurrences of such a comparison will be replaced, regardless of surrounding control structure.

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Replace Concatenation with Infix-Operation

This rule replaces the 'concat()' method on 'Strings' with the + operator.

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Replace For-Loop with Stream::forEach

This rule replaces enhanced for loops (for-each-loops) with an invocation of 'java.util.stream.Stream::forEach' method and passes the body of the for-loop as a lambda Consumer parameter.

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Split Multiple Variable Declarations

Multiple field or variable declarations on the same line could cause confusion about their types and initial values. That also makes it harder to read and to understand the code. In order to improve readability, each field or variable should be declared on a separate line. This is recommended by the Code Conventions for the Java Programming Language.

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Replace While-Loop with Enhanced For-Loop

While-loops over Iterators which could be expressed with a for-loop, are transformed to an equivalent for-loop.

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Replace Map::get by Map::getOrDefault

Java 8 introduced 'Map::getOrDefault' which offers the possibility to return a default value if the map does not contain a mapping for the given key. This rule replaces the invocations of 'Map::get' followed by a null-check with 'Map::getOrDefault'.

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Replace Inefficient Constructors with valueOf()

All calls to a constructor of a primitive type will be replaced by the corresponding static 'valueOf()' method. For example 'new Integer("1")' becomes 'Integer.valueOf("1")'.

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Replace indexOf() with contains()

This rule replaces calls to 'indexOf()' on instances of Strings or Collections with calls to the 'contains()' method. 'contains()' was introduced in Java 1.4 and helps to make the code more readable.

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Replace For-Loop with Stream::collect(Collectors.joining())

This rule refactors the enhanced for loops which are only being used for concatenating the elements of collections or arrays.

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Replace put(..) with putIfAbsent(..)

If 'map.put(..)' is wrapped with a condition verifying the existence of an element one can use 'map.putIfAbsent(...)' instead.

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Replace static final Collections with Collections.unmodifiable...()

Wraps the initialization of a final collection with 'Collections.unmodifiable...()'

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Replace removeAll() with clear()

Simplifies the code by replacing all occurrences of 'removeAll()' which have the current collection as parameter with 'clear()'.

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Replace For-Loop with Stream::Match

Replaces occurrences of enhanced for-loops which are only used to initialize or return a boolean variable with 'Stream::anyMatch', 'Stream::allMatch' or 'Stream::noneMatch'. The stream syntax is more concise and improves readability.

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Replace For-Loop with Enhanced-For-Loop

Transforms all possible for loops with iterators to a ForEach loop.

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Replace Nested Loops with flatMap

Nested For-Loops or invocations of forEach commonly used to iterate over all elements of a collection of collections, can be avoided by using flatMap(). Using 'flatMap()' makes code much more readable and can be combined with other stream functions.

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Replace equals() on Enum Constants

Replaces occurrences of 'equals()' on Enum constants with an identity comparison (==). In the case the equals relation is wrapped with an boolean negation the result will be an not equals (!=).

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Replace For-Loop with Stream::findFirst

Replaces enhanced for-loops which are used to find an element within a collection by a stream and uses 'Stream::findFirst' to find the result. By using the stream syntax, a multi-line control statement can be reduced to a single line.

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Replace For-Loop with Stream::takeWhile

The Stream API in Java 9 is extended with the 'takeWhile' method to get the prefix of a stream. This rule replaces the enhanced for-loops with a stream iterating over the prefix of a collection with 'Stream::takeWhile'.

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Use Portable Newline

It is generally preferable better to use "%n", which will produce the platform-specific line separator.

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Use Stream::filter

This rule transforms an if-Statement (without an else statement), which wraps the whole execution block of a 'Stream::forEach' method into a call to 'Stream::filter' with a lambda expression (Predicate) as parameter. This lambda is constructed using the expression from the if-Statement.

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Use Optional::ifPresentOrElse

It is common to have an else-statement following an Optional.isPresent check. One of the extensions of the Optional API in Java 9 is Optional.ifPresentOrElse, which performs either a Consumer or a Runnable depending on the presence of the value. This rule replaces an 'isPresent' check followed by an else-statement with a single 'ifPresentOrElse' invocation.

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Use Functional Interfaces

Converts anonymous inner classes to equivalent lambda expressions.

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Use Factory Methods for Collections

Replaces the invocations of 'Collections.unmodifiableList/Set/Map' with the corresponding factory method 'List.of', 'Set.of' and 'Map.ofEntries' introduced in Java 9.

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System Out To Logging

Replaces the standard output statements with logger statements when possible.

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Use Guard Condition

Replaces the last statement of a method with a guard condition.

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StringBuffer() to StringBuilder()

This rule changes the type of local variables from 'StringBuffer()' to 'StringBuilder()'.

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Use Local Variable Type Inference

This rule replaces the types on the local variable declarations with the reserved word var introduced in Java 10.

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Use Multi Catch

Java 7 introduced the possibility to merge multiple catch clauses into a single multi-catch clause. Merging is only possible if the catch statements are identical.

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Use Optional::ifPresent

The usage of 'Optional.get' should be avoided in general because it can potentially throw a NoSuchElementException (it is likely to be deprecated in future releases). It is often the case that the invocation of 'Optional.get' is wrapped by a condition that uses 'Optional.isPresent'. Such cases can be replaced with the 'Optional.ifPresent(Consumer<? super T> consumer)'.

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Use BufferedReader::lines

Replaces While-Loops and For-Loops that are using 'BufferedReader::readLine' to iterate through lines of a file by a stream generated with 'BufferedReader::lines'.

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Use List Sort

Replace static invocations of 'Collections.sort(List, Comparator)' with 'List.sort(Comparator)'.

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Use Stream::collect

Replaces 'Stream::forEach' with 'Stream::collect' if the argument of the 'forEach' statement is only used for adding elements to a list. This simplifies adding elements to a list.

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Use Collections Singleton List

Replaces Arrays.asList with 0 or 1 parameters respectively with Collections.emptyList() or Collections.singletonList(..)

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Use Stream::map

Extracts a block from the body of the consumer of the 'Stream::forEach' method and introduces 'Stream::map' instead. This makes complicated code blocks easier to read and reuse.

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Use String Literals

Removes all class instantiations from 'String' if its parameter is empty or a 'String'.

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Use StringBuilder::append

Replaces the infix operator + on String concatenation by 'StringBuilder::append'

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Use StringUtils Methods

Replaces various 'String' methods with their null-safe counterparts from 'StringUtils'.

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Use Try-With-Resource

This rule adds the try-with-resources statement introduced in Java 7. Closing statements are removed as the construct takes care of that.

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Use equals() on Primitive Objects

This rule replaces the infix operators "==" and "!=" with 'equals()' when used on primitive objects.

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