Java Hints

Contents 1 APIs 2 Assignment Issues 3 Bitwise Operations 4 Braces 5 Class Structure 6 Code Maturity Issues 7 Empty Statements 8 Encapsulation 9 Error Fixes 10 Finalization 11 General 12 Imports 13 Initialization 14 JDK 1.5 and later 15 Javadoc 16 Logging 17 Maven 18 NetBeans Development 19 Performance 20 Probable Bugs 21 Standard Javac Warnings 22 Suggestions 23 Threading

APIs

Exporting non-public type through public API

Checks that return types and parameter types of allpublic methods and all types of public fields are publicly available from other packages.Having private or package private types in a package API is useless.

Utility class with visible constructor

Finds out classes containing only static elements with public or protected constructors.

Utility class without constructor

Finds out classes containing only static elements and still being instantiable.

Assignment Issues

Assignment replaceable with operator-assignment

Reports instances of assignment operations which can be replaced by operator-assignment. Code using operator-assignment may be clearer, and theoretically more performant. Since NetBeans 6.9

Assignment to catch-block parameter

Reports any instances of assignment to variable declared as a catch block parameter. While occasionally intended, this construct can be confusing. Since NetBeans 6.9

Assignment to for-loop parameter

Reports any instances of assignment to variable declared in a for statement in the body of that statement. It also reports any attempt to increment or decrement the variable. While occasionally intended, this construct can be extremely confusing, and is often the result of a typo. Since NetBeans 6.9

Assignment to method parameter

Reports any instances of assignment to a variable declared as a method parameter. It also reports any attempt to increment or decrement the variable. While occasionally intended, this construct can be extremely confusing, and is often the result of a typo. Since NetBeans 6.9

Nested assignment

Reports any instances of assignment expressions nested inside other expressions. While admirably terse, such expressions may be confusing, and violate the general design principle that a given construct should do precisely one thing. Since NetBeans 6.9

Value of increment/decrement expression used

Reports any instances of increment or decrement expressions nested inside other expressions. While admirably terse, such expressions may be confusing, and violate the general design principle that a given construct should do precisely one thing. Since NetBeans 6.9

Bitwise Operations

Incompatible mask

This inspection reports any instances of bitwise mask expressions which are guaranteed to evaluate to false. Expressions checked are of the form (var & constant1) == constant2 or (var | constant1) == constant2, where constant1and constant2 are incompatible bitmask constants. Since NetBeans 6.9

Pointless bitwise expression

This inspection reports any instances of pointless bitwise expressions. Such expressions include anding with zero, oring by zero, and shift by zero. Such expressions may be the result of automated refactorings not completely followed through to completion, and in any case are unlikely to be what the developer intended to do. Since NetBeans 6.9

Shift operation outside of the reasonable range

This inspection reports any instances of shift operations where the value shifted by is constant and outside of the reasonable range. Integer shift operations outside of the range 0..31 and long shift operations outside of therange 0..63 are reported. Shifting by negative or overly large values is almost certainly a coding error. Since NetBeans 6.9

Braces

Do-While Loops Must Use Braces

Do-While Loops Must Use Braces

For Loops Must Use Braces

Warns if a for loop does not
have its body wrapped in curly braces.

If-Else Statements Must Use Braces

If-Else Statements Must Use Braces

While Loops Must Use Braces

While Loops Must Use Braces

Class Structure

Class may be interface

Reports any concrete or abstract classes which may be simplified to be interfaces. This occurs if the class has no superclass (other than Object), has no fields declared that are not static, final, and public, and has no methods declared that are not public and abstract, and no inner classes that cannot themselves be interfaces. Since NetBeans 6.9

Final class

Reports any instances of classes being declared final. Some coding standards discourage final classes. Since NetBeans 6.9

Final method

Reports any instances of methods being declared final. Some coding standards discourage final classes. Since NetBeans 6.9

Final method in final class

Reports any instances of methods being declared final in classes that are declared final. This is unnecessary, and may be confusing. Since NetBeans 6.9

Final private method

Reports any instances of methods being declared final and private. As private methods cannot be meaningfully overridden, declaring them final is redundant. Since NetBeans 6.9

Final static method

Reports any instances of methods being declared final and static. As static methods cannot be meaningfully overridden, declaring them final is redundant. Since NetBeans 6.9

Marker interface

Reports marker interfaces which have no methods or fields. Such interfaces may be confusing, and normally indicate a design failure. Interfaces which extend two or more other interfaces will not be reported. Since NetBeans 6.9

Multiple top-level classes in file

Reports any instances of multiple top-level classes in a single java file. Putting multiple top-level classes in a file can be confusing, and may degrade the usefulness of various software tools. Since NetBeans 6.9

No-op method in abstract class

Reports any instances of no-op methods in abstract classes. It is usually a better design to make such methods abstract themselves, so that classes which inherit the methods will not forget to provide their own implementations. Since NetBeans 6.9

Protected member in final class

Reports any instances of members being declared protected in classes that are declared final. Such members may be declared private or package-visible instead. Since NetBeans 6.9

Public constructor in non-public class

Reports all constructors in non-public classes that are declared public. Since NetBeans 6.9

Code Maturity Issues

Obsolete Collection

This inspection reports any uses of java.util.Vector or java.util.Hashtable. While still supported, these classes were made obsolete by the JDK1.2 collection classes, and should probably not be used in new development. Since NetBeans 6.9

Print Stack Trace

This inspection reports any uses Throwable.printStackTrace() without arguments. These are often temporary debugging statements, and should probably be either removed from production code, or replaced by a more robust logging facility. Since NetBeans 6.9

System out / err

This inspection reports any uses of System.out or System.err. These are often temporary debugging statements, and should probably be either removed from production code, or replaced by a more robust logging facility. Since NetBeans 6.9

Thread Dump Stack

This inspection reports any uses Thread.dumpStack().These are often temporary debugging statements, and should probably be either removed from production code,or replaced by a more robust logging facility. Since NetBeans 6.9

Empty Statements

Empty statement

Checks for empty statements in blocks usually representedas superfluous semicolon. Since NetBeans 6.9

Empty statement after 'do'

Checks for 'do/while' statements in form
do;
while. Since NetBeans 6.9

Empty statement after 'for'

Checks for 'for' statements in form
for(...);. Since NetBeans 6.9

Empty statement after 'if/else'

Checks for 'if/else' statements in form
if(...);
else;. Since NetBeans 6.9

Empty statement after 'while'

Checks for 'while' statements in form
while(...);. Since NetBeans 6.9

Encapsulation

Access of Private Field of Another Object

Warns about access of private fields of another objects Since NetBeans 6.9

Assignment to Array Field from Parameter

Warns about assignment of array into fields Since NetBeans 6.9

Assignment to Collection Field from Parameter

Warns about assignment of java.util.Collection into fields Since NetBeans 6.9

Assignment to Date or Calendar Field from Parameter

Warns about assignment of java.util.Date or java.util.Calendar into fields Since NetBeans 6.9

Package Field

Warns about existence of package visible variables Since NetBeans 6.9

Package Visible Inner Class

Warns about existence of package visible inner class Since NetBeans 6.9

Protected Field

Warns about existence of protected variables Since NetBeans 6.9

Protected Inner Class

Warns about existence of protected visible inner class Since NetBeans 6.9

Public Field

Warns about existence of public variables Since NetBeans 6.9

Public Inner Class

Warns about existence of public visible inner class Since NetBeans 6.9

Return of Array Field

Warns about return of array fields Since NetBeans 6.9

Return of Collection Field

Warns about return of collection fields Since NetBeans 6.9

Return of Date or Calendar Field

Warns about return of java.util.Date or java.util.Calendar fields Since NetBeans 6.9

Error Fixes

Create Field

Settings for Create Field Fix Since NetBeans 6.9

Create Local Variable

Settings for the Create Local Variable error fix Since NetBeans 6.9

Surround with try-catch

Settings for the Surround with try-catch error fix Since NetBeans 6.9

Finalization

finalize() called explicitly

Warns about an explicit call of the Object.finalize() Since NetBeans 6.9

finalize() declared

Warns about implementations of Object.finalize() Since NetBeans 6.9

finalize() does not call super.finalize()

Warns about implementations of Object.finalize() which do not call supertype implementation Since NetBeans 6.9

finalize() not declared protected

Warns about non protected implementations of Object.finalize() Since NetBeans 6.9

General

.equals Method not Checking Type

Implementation of .equals methods not checking the type of the input parameter

Accessing static via reference

Java language allows access to static fields thru instance variables, however this is often misleading and harder to read.

Assignment To Itself

Assignment To Itself

Comparing Strings using == or !=

Checks for usages of == or != operator for comparing Strings.
String comparisons should generally be done using the equals() method.

Field hides another field

Declaration of a field in a class can hide declaration of another field in superclasses. Although possible, this is not very good programming style.

Generate missing hashCode or equals

Checks whether a class which overrides equals method also overrides hashCode.

Local variable hides a field

Declaration of a variable in a method can hide declaration of a field declared in the surrounding class. Although possible, this is not very good programming style.

Remove Unnecessary Return Statement

Remove Unnecessary Return Statement Since NetBeans 7.1

Unnecessary Throwable.initCause

Finds invocations of Throwable.initCause which can be replaced with simple constructor invocation. When the "Never alter result of getMessage()" checkbox is unchecked, (IllegalStateException) new IllegalStateException().initCause(ex) will be rewritten to new IllegalStateException(ex), which will alter the value of getMessage(). When the checkbox is checked, the code will become new IllegalStateException(null, ex). Similar rule holds for creating the exception from getMessage() or getLocalizedMessage() of the cause. Since NetBeans 6.9

Wrong Package

Wrong Package

Imports

Import From The Same Package

Import From The Same Package

Import From java.lang Package

Import From java.lang Package

Import from Excluded

Import from package or class which has been labelled "Excluded" in the Code Completer

Organize imports

Checks whether import statements correspond to the specified code style rules Since NetBeans 7.1

Star import

Star import

Unused Import

Unused Import

Initialization

Passing suspicious parameter in the constructor

Using this as parameter can be dangerous in the contructor because the object is not fully initialized. Since NetBeans 6.9

Problematic call in the constructor

Calling methods that can be overridden can be dangerous in the contructor because in the moment when the overridden method is called the object is not fully initialized. Since NetBeans 6.9

Static non-final variable used during initialization

Using static non-final variables can be dangerous in the initialization code because their values may depend on the order of initialization statements Since NetBeans 6.9

JDK 1.5 and later

AbstractProcessor.getSupportedAnnotations() is overridden

Overriding Processor.getSupportedAnnotations() may lead to unnecessary classloading during development, and may prevent important optimalizations. consider using @javax.annotation.processing.SupportedAnnotationTypes In current development version

Add @Override Annotation

Add @Override Annotation

Add Underscores

Proposed to add underscores to integer literals to improve their readability In current development version

Can Use Diamond

Warns about places where the diamond operator in JDK 7 can be used instead of explicit type parameters Since NetBeans 7.1

Convert to try-with-resources

Converts try finally block to try-with-resources Since NetBeans 7.0

Don't use Annotation as super interface

Despite the compiler permitting such constructs,Annotations should not be used as superinterfaces.

Join catch sections using multicatch

Join catch sections using multicatch Since NetBeans 7.0

Static imports

Convert method to static import. Feedback to http://www.netbeans.org/issues/show_bug.cgi?id=89258 Since NetBeans 6.9

Use specific catch

Converts catch (Throwable) or catch (Exception) to multicatch catching the exceptions thrown by the try body. Since NetBeans 7.0

Use switch over Strings where possible.

Marks cascades of ifs which can be converted to switch over Strings . Since NetBeans 6.9

Javadoc

Create Javadoc

Create Javadoc

Error in Javadoc

Error in Javadoc

Logging

Logger declaration is not static final

Each class should have one unique logger. If declared as a field it should be static and final. Since NetBeans 6.9

Multiple loggers

There are several loggers declared for a single class. Since NetBeans 6.9

No loggers

There is no logger declared for a class. Since NetBeans 6.9

String concatenation in logger

It is not performance efficient to concatenate strings in logger messages. It is better to use a template message with placeholders that are replaced by concrete values only when the message is really going to be logged. Since NetBeans 6.9

Maven

Resolve Missing Class Dependency

Resolve missing class dependency and add to project POM Since NetBeans 6.9

NetBeans Development

Empty cancel() for cancelable tasks

Warn about empty cancel() methods for cancelable tasks

HelpCtx issues

Warnings about misuse of org.openide.util.HelpCtx. In current development version

Illegal Use of instanceOf operator

Show illegal use of instanceof on javax.lang.model.elements, javax.lang.model.type and com.sun.source.tree

Use @NbBundle.Messages

Use @NbBundle.Messages in preference to Bundle.properties plus NbBundle.getMessage(...). Since NetBeans 7.0

Performance

.getClass() replaceable with .class

Finds instantions of a class directly followed by invocation of .getClass() on the newly constructed object Since NetBeans 6.9

Collections without initial capacity

Looks for instatiations of collections with missing initial capacity. Only collections backed-up with an array are tested. Since NetBeans 6.9

Creating new Boolean

Creating new Boolean is inefficient and typically useless. Since NetBeans 6.9

Length one String in String.indexOf

Length one String literal in String.indexOf can be replaced with a character literal Since NetBeans 6.9

Manual array copy

Finds occurrences of manual array copying via for loop Since NetBeans 6.9

Map replaceable with EnumMap

Finds instantiations of Maps that can be replaced with EnumMap Since NetBeans 6.9

Set replaceable with EnumSet

Finds instantiations of Sets that can be replaced with EnumSet Since NetBeans 6.9

String concatenation in StringBuilder.append

Looks for string concatenation in the parameter of an invocation of the append method of StringBuilder or StringBuffer. Since NetBeans 6.9

String constructor

Use of java.lang.String constructor is usually useless. Since NetBeans 6.9

String.equals("")

Use of String.equals("") can be replaced with with String.length() == 0 (for JDK5 and lower) or String.isEmpty() (for JDK6 and higher) Since NetBeans 6.9

String.intern() called on constant

Invocations of String.intern() on compile-time constants are superfluous. Since NetBeans 6.9

StringBuilder without initial capacity

Looks for instantiations of StringBuilder or StringBuffer with missing initial capacity. Since NetBeans 6.9

Usage of .size() == 0

Use .isEmpty() or !.isEmpty() instead of .size() == 0 or .size() != 0 where possible. Since NetBeans 6.9

Useless use of StringBuffer

Use StringBuilder instead of StringBuffer where possible. Since NetBeans 6.9

Zero element array passed to Collection.toArray

Passing zero element array to Collection.toArray may affect performance In current development version

Probable Bugs

.equals on Array

.equals on array Since NetBeans 6.9

.equals on Incompatible Types

.equals on incompatible types

.equals(null)

Finds invocations of the Object.equals method with literal parameter 'null'. Since NetBeans 6.9

@CheckReturnValue

Verifies that a result of method marked with @CheckReturnValue is really checked. In current development version

Annotations without runtime Retention

Warns about reflective access to annotations with CLASS or SOURCE retentions Since NetBeans 6.9

Dead Branch

Dead Branch Since NetBeans 7.1

Incompatible cast/instanceof

Incompatible cast surrounded with incompatible instanceof Since NetBeans 6.9

Incorrect column index in ResultSet

Reports Iincorrect column indices passed to various methods of java.sql.ResultSet Since NetBeans 6.9

Malformed regular expression

Warns about malformed regular expressions Since NetBeans 6.9

Result of new Object ignored

Result of new Object ignored. Since NetBeans 6.9

String.replaceAll(".", )

Finds occurrences of calls to String.replaceAll(".", $target), which would replace all characters of the source string with $target. Since NetBeans 6.9

Suspicious invocation of System.arraycopy

Finds invocations of System.arraycopy with negative offsets, length or used on non-array objects. Since NetBeans 6.9

Suspicious method call

Warns about suspicious calls to Collection.remove/contains and Map.containsKey/containsValue/remove Since NetBeans 6.9

Synchronizing on this in anonymous class

<html>Synchronizing on this in anonymous or local class is probably a result of refactoring and possibly a mistake Since NetBeans 6.9

Unbalanced read/write with arrays

Unbalanced read/write with arrays Since NetBeans 7.1

Unbalanced read/write with collections

Unbalanced read/write with collections Since NetBeans 7.1

Unused Assignment

Unused Assignment Since NetBeans 7.1

Standard Javac Warnings

Deprecated

Warn when code uses deprecated API. Since NetBeans 6.9

Division By Zero

Division By Zero Since NetBeans 6.9

Empty Statement After If

Empty Statement After If Since NetBeans 6.9

Fallthrough

Warn when a case can fall through to the next case. Since NetBeans 6.9

Finally

Warn when a finally block interrupts flow of a try/catch block. Since NetBeans 6.9

Overrides

Warn when an overriding method is not annotated with @Overrides Since NetBeans 6.9

Raw Types

Raw Types Since NetBeans 6.9

Serialization

Warn when a class which implements java.io.Serializable does not declare a serialVersionUID. Since NetBeans 6.9

Unchecked

Warn when unchecked conversions may cause ClassCastExceptions at runtime. Since NetBeans 6.9

Unnecessary Cast

Warn when an object is cast unnecessarily to the same type or a supertype. Since NetBeans 6.9

Suggestions

Assign Return Value To New Variable

Assign Return Value To New Variable

Assign Unused Constructor Parameter to Field

Assign Unused Constructor Parameter to Field

Convert Anonymous to Member

Convert Anonymous to Member

Convert integer constant to different base

Convert integer constant to different base Since NetBeans 7.0

Create Subclass

Create Subclass In current development version

Declaration for instanceof

Declaration for instanceof

Expand Enhanced For Loop

Expand Enhanced For Loop Since NetBeans 7.1

Fill Missing Cases to Switch

Adds missing cases to switch statement. The default clause template should be one Java statement, occurrences of $expression will be replaced with the expression over which the switch statement works. In current development version

Flip .equals

Allows to flip .equals parameter and call site Since NetBeans 6.9

Split Declaration

Splits declaration with initializer to a declaration and assignment In current development version

Threading

.wait invoked outside a synchronized context

.wait invoked outside a synchronized context Since NetBeans 6.9

.wait invoked outside a synchronized context

.wait invoked outside a synchronized context Since NetBeans 6.9

Double-checked locking

Searches for examples of double checked locking - e.g.when a variable is tested before as well as inside a synchronized block.

Empty synchronized block

Empty synchronized block are usually useless Since NetBeans 6.9

Invoking Condition.notify()

Invoking notify or notifyAll on java.util.concurrent.locks.Condition should probably be replaced with invoking signal or signalAll. Since NetBeans 6.9

Invoking Condition.wait()

Invoking notify or notifyAll on java.util.concurrent.locks.Condition is probably unintended. Since NetBeans 6.9

Invoking Thread.run()

Invoking run on java.lang.Thread should be probably replaced with invocation of method start() Since NetBeans 6.9

Invoking Thread.stop()/suspend()/resume()

Methods stop(), suspend() and resume() of java.lang.Thread are dangerous and should not be used. Since NetBeans 6.9

Invoking Thread.yield()

Invocation of method yield() on java.lang.Thread is usually used to masquerade synchronization problems and should be avoided. Since NetBeans 6.9

Lock not unlocked in finally

Finds occurrences of Lock.lock()-Lock.unlock() not properly wrapped in try-finally. Since NetBeans 6.9

Nested synchronized blocks

Nesting synchronized blocks is either useless (if they use the same lock object) or dangerous. Since NetBeans 6.9

Starting Thread in constructor

Starting a new Thread in constructor is dangerous and should be prevented. Since NetBeans 6.9

Synchronization on non-final field

Synchronization on non-final field

Synchronizing on Lock

Synchronizing on java.util.concurrent.locks.Lock is usually unintended and should be replaced with Lock.lock()-Lock.unlock() Since NetBeans 6.9

Thread.sleep in loop

Invoking Thread.sleep in loop can cause performance problems Since NetBeans 6.9

Thread.sleep in synchronized context

Invoking Thread.sleep in synchronized context can cause performance problems Since NetBeans 6.9

Volatile array field

Finds declarations of volatile array fields. Since NetBeans 6.9