org.apache.commons.lang

Class ClassUtils

public class ClassUtils extends Object

Operates on classes without using reflection.

This class handles invalid null inputs as best it can. Each method documents its behaviour in more detail.

Since: 2.0

Version: $Id: ClassUtils.java 633621 2008-03-04 20:20:23Z mbenson $

Author: Stephen Colebourne Gary Gregory Norm Deane Alban Peignier Tomasz Blachowicz

Field Summary
static StringINNER_CLASS_SEPARATOR

The inner class separator String: "$".

static charINNER_CLASS_SEPARATOR_CHAR

The inner class separator character: '$' == {@value }.

static StringPACKAGE_SEPARATOR

The package separator String: ".".

static charPACKAGE_SEPARATOR_CHAR

The package separator character: '.' == {@value }.

Constructor Summary
ClassUtils()

ClassUtils instances should NOT be constructed in standard programming.

Method Summary
static ListconvertClassesToClassNames(List classes)

Given a List of Class objects, this method converts them into class names.

A new List is returned.

static ListconvertClassNamesToClasses(List classNames)

Given a List of class names, this method converts them into classes.

A new List is returned.

static ListgetAllInterfaces(Class cls)

Gets a List of all interfaces implemented by the given class and its superclasses.

The order is determined by looking through each interface in turn as declared in the source file and following its hierarchy up.

static ListgetAllSuperclasses(Class cls)

Gets a List of superclasses for the given class.

static ClassgetClass(ClassLoader classLoader, String className, boolean initialize)
Returns the class represented by className using the classLoader.
static ClassgetClass(ClassLoader classLoader, String className)
Returns the (initialized) class represented by className using the classLoader.
static ClassgetClass(String className)
Returns the (initialized )class represented by className using the current thread's context class loader.
static ClassgetClass(String className, boolean initialize)
Returns the class represented by className using the current thread's context class loader.
static StringgetPackageCanonicalName(Object object, String valueIfNull)

Gets the package name from the canonical name of an Object.

static StringgetPackageCanonicalName(Class cls)

Gets the package name from the canonical name of a Class.

static StringgetPackageCanonicalName(String canonicalName)

Gets the package name from the canonical name.

static StringgetPackageName(Object object, String valueIfNull)

Gets the package name of an Object.

static StringgetPackageName(Class cls)

Gets the package name of a Class.

static StringgetPackageName(String className)

Gets the package name from a String.

The string passed in is assumed to be a class name - it is not checked.

If the class is unpackaged, return an empty string.

static MethodgetPublicMethod(Class cls, String methodName, Class[] parameterTypes)

Returns the desired Method much like Class.getMethod, however it ensures that the returned Method is from a public class or interface and not from an anonymous inner class.

static StringgetShortCanonicalName(Object object, String valueIfNull)

Gets the canonical name minus the package name for an Object.

static StringgetShortCanonicalName(Class cls)

Gets the canonical name minus the package name from a Class.

static StringgetShortCanonicalName(String canonicalName)

Gets the canonical name minus the package name from a String.

The string passed in is assumed to be a canonical name - it is not checked.

static StringgetShortClassName(Object object, String valueIfNull)

Gets the class name minus the package name for an Object.

static StringgetShortClassName(Class cls)

Gets the class name minus the package name from a Class.

static StringgetShortClassName(String className)

Gets the class name minus the package name from a String.

The string passed in is assumed to be a class name - it is not checked.

static booleanisAssignable(Class[] classArray, Class[] toClassArray)

Checks if an array of Classes can be assigned to another array of Classes.

This method calls isAssignable for each Class pair in the input arrays.

static booleanisAssignable(Class cls, Class toClass)

Checks if one Class can be assigned to a variable of another Class.

Unlike the Class#isAssignableFrom(java.lang.Class) method, this method takes into account widenings of primitive classes and nulls.

Primitive widenings allow an int to be assigned to a long, float or double.

static booleanisInnerClass(Class cls)

Is the specified class an inner class or static nested class.

static Class[]primitivesToWrappers(Class[] classes)

Converts the specified array of primitive Class objects to an array of its corresponding wrapper Class objects.

static ClassprimitiveToWrapper(Class cls)

Converts the specified primitive Class object to its corresponding wrapper Class object.

NOTE: From v2.2, this method handles Void.TYPE, returning Void.TYPE.

static Class[]toClass(Object[] array)

Converts an array of Object in to an array of Class objects.

This method returns null for a null input array.

static Class[]wrappersToPrimitives(Class[] classes)

Converts the specified array of wrapper Class objects to an array of its corresponding primitive Class objects.

This method invokes wrapperToPrimitive() for each element of the passed in array.

static ClasswrapperToPrimitive(Class cls)

Converts the specified wrapper class to its corresponding primitive class.

This method is the counter part of primitiveToWrapper().

Field Detail

INNER_CLASS_SEPARATOR

public static final String INNER_CLASS_SEPARATOR

The inner class separator String: "$".

INNER_CLASS_SEPARATOR_CHAR

public static final char INNER_CLASS_SEPARATOR_CHAR

The inner class separator character: '$' == {@value }.

PACKAGE_SEPARATOR

public static final String PACKAGE_SEPARATOR

The package separator String: ".".

PACKAGE_SEPARATOR_CHAR

public static final char PACKAGE_SEPARATOR_CHAR

The package separator character: '.' == {@value }.

Constructor Detail

ClassUtils

public ClassUtils()

ClassUtils instances should NOT be constructed in standard programming. Instead, the class should be used as ClassUtils.getShortClassName(cls).

This constructor is public to permit tools that require a JavaBean instance to operate.

Method Detail

convertClassesToClassNames

public static List convertClassesToClassNames(List classes)

Given a List of Class objects, this method converts them into class names.

A new List is returned. null objects will be copied into the returned list as null.

Parameters: classes the classes to change

Returns: a List of class names corresponding to the Class objects, null if null input

Throws: ClassCastException if classes contains a non-Class entry

convertClassNamesToClasses

public static List convertClassNamesToClasses(List classNames)

Given a List of class names, this method converts them into classes.

A new List is returned. If the class name cannot be found, null is stored in the List. If the class name in the List is null, null is stored in the output List.

Parameters: classNames the classNames to change

Returns: a List of Class objects corresponding to the class names, null if null input

Throws: ClassCastException if classNames contains a non String entry

getAllInterfaces

public static List getAllInterfaces(Class cls)

Gets a List of all interfaces implemented by the given class and its superclasses.

The order is determined by looking through each interface in turn as declared in the source file and following its hierarchy up. Then each superclass is considered in the same way. Later duplicates are ignored, so the order is maintained.

Parameters: cls the class to look up, may be null

Returns: the List of interfaces in order, null if null input

getAllSuperclasses

public static List getAllSuperclasses(Class cls)

Gets a List of superclasses for the given class.

Parameters: cls the class to look up, may be null

Returns: the List of superclasses in order going up from this one null if null input

getClass

public static Class getClass(ClassLoader classLoader, String className, boolean initialize)
Returns the class represented by className using the classLoader. This implementation supports names like "java.lang.String[]" as well as "[Ljava.lang.String;".

Parameters: classLoader the class loader to use to load the class className the class name initialize whether the class must be initialized

Returns: the class represented by className using the classLoader

Throws: ClassNotFoundException if the class is not found

getClass

public static Class getClass(ClassLoader classLoader, String className)
Returns the (initialized) class represented by className using the classLoader. This implementation supports names like "java.lang.String[]" as well as "[Ljava.lang.String;".

Parameters: classLoader the class loader to use to load the class className the class name

Returns: the class represented by className using the classLoader

Throws: ClassNotFoundException if the class is not found

getClass

public static Class getClass(String className)
Returns the (initialized )class represented by className using the current thread's context class loader. This implementation supports names like "java.lang.String[]" as well as "[Ljava.lang.String;".

Parameters: className the class name

Returns: the class represented by className using the current thread's context class loader

Throws: ClassNotFoundException if the class is not found

getClass

public static Class getClass(String className, boolean initialize)
Returns the class represented by className using the current thread's context class loader. This implementation supports names like "java.lang.String[]" as well as "[Ljava.lang.String;".

Parameters: className the class name initialize whether the class must be initialized

Returns: the class represented by className using the current thread's context class loader

Throws: ClassNotFoundException if the class is not found

getPackageCanonicalName

public static String getPackageCanonicalName(Object object, String valueIfNull)

Gets the package name from the canonical name of an Object.

Parameters: object the class to get the package name for, may be null valueIfNull the value to return if null

Returns: the package name of the object, or the null value

Since: 2.4

getPackageCanonicalName

public static String getPackageCanonicalName(Class cls)

Gets the package name from the canonical name of a Class.

Parameters: cls the class to get the package name for, may be null.

Returns: the package name or an empty string

Since: 2.4

getPackageCanonicalName

public static String getPackageCanonicalName(String canonicalName)

Gets the package name from the canonical name.

The string passed in is assumed to be a canonical name - it is not checked.

If the class is unpackaged, return an empty string.

Parameters: canonicalName the canonical name to get the package name for, may be null

Returns: the package name or an empty string

Since: 2.4

getPackageName

public static String getPackageName(Object object, String valueIfNull)

Gets the package name of an Object.

Parameters: object the class to get the package name for, may be null valueIfNull the value to return if null

Returns: the package name of the object, or the null value

getPackageName

public static String getPackageName(Class cls)

Gets the package name of a Class.

Parameters: cls the class to get the package name for, may be null.

Returns: the package name or an empty string

getPackageName

public static String getPackageName(String className)

Gets the package name from a String.

The string passed in is assumed to be a class name - it is not checked.

If the class is unpackaged, return an empty string.

Parameters: className the className to get the package name for, may be null

Returns: the package name or an empty string

getPublicMethod

public static Method getPublicMethod(Class cls, String methodName, Class[] parameterTypes)

Returns the desired Method much like Class.getMethod, however it ensures that the returned Method is from a public class or interface and not from an anonymous inner class. This means that the Method is invokable and doesn't fall foul of Java bug 4071957).

Set set = Collections.unmodifiableSet(...);
  Method method = ClassUtils.getPublicMethod(set.getClass(), "isEmpty",  new Class[0]);
  Object result = method.invoke(set, new Object[]);

Parameters: cls the class to check, not null methodName the name of the method parameterTypes the list of parameters

Returns: the method

Throws: NullPointerException if the class is null SecurityException if a a security violation occured NoSuchMethodException if the method is not found in the given class or if the metothod doen't conform with the requirements

getShortCanonicalName

public static String getShortCanonicalName(Object object, String valueIfNull)

Gets the canonical name minus the package name for an Object.

Parameters: object the class to get the short name for, may be null valueIfNull the value to return if null

Returns: the canonical name of the object without the package name, or the null value

Since: 2.4

getShortCanonicalName

public static String getShortCanonicalName(Class cls)

Gets the canonical name minus the package name from a Class.

Parameters: cls the class to get the short name for.

Returns: the canonical name without the package name or an empty string

Since: 2.4

getShortCanonicalName

public static String getShortCanonicalName(String canonicalName)

Gets the canonical name minus the package name from a String.

The string passed in is assumed to be a canonical name - it is not checked.

Parameters: canonicalName the class name to get the short name for

Returns: the canonical name of the class without the package name or an empty string

Since: 2.4

getShortClassName

public static String getShortClassName(Object object, String valueIfNull)

Gets the class name minus the package name for an Object.

Parameters: object the class to get the short name for, may be null valueIfNull the value to return if null

Returns: the class name of the object without the package name, or the null value

getShortClassName

public static String getShortClassName(Class cls)

Gets the class name minus the package name from a Class.

Parameters: cls the class to get the short name for.

Returns: the class name without the package name or an empty string

getShortClassName

public static String getShortClassName(String className)

Gets the class name minus the package name from a String.

The string passed in is assumed to be a class name - it is not checked.

Parameters: className the className to get the short name for

Returns: the class name of the class without the package name or an empty string

isAssignable

public static boolean isAssignable(Class[] classArray, Class[] toClassArray)

Checks if an array of Classes can be assigned to another array of Classes.

This method calls isAssignable for each Class pair in the input arrays. It can be used to check if a set of arguments (the first parameter) are suitably compatible with a set of method parameter types (the second parameter).

Unlike the Class#isAssignableFrom(java.lang.Class) method, this method takes into account widenings of primitive classes and nulls.

Primitive widenings allow an int to be assigned to a long, float or double. This method returns the correct result for these cases.

Null may be assigned to any reference type. This method will return true if null is passed in and the toClass is non-primitive.

Specifically, this method tests whether the type represented by the specified Class parameter can be converted to the type represented by this Class object via an identity conversion widening primitive or widening reference conversion. See The Java Language Specification, sections 5.1.1, 5.1.2 and 5.1.4 for details.

Parameters: classArray the array of Classes to check, may be null toClassArray the array of Classes to try to assign into, may be null

Returns: true if assignment possible

isAssignable

public static boolean isAssignable(Class cls, Class toClass)

Checks if one Class can be assigned to a variable of another Class.

Unlike the Class#isAssignableFrom(java.lang.Class) method, this method takes into account widenings of primitive classes and nulls.

Primitive widenings allow an int to be assigned to a long, float or double. This method returns the correct result for these cases.

Null may be assigned to any reference type. This method will return true if null is passed in and the toClass is non-primitive.

Specifically, this method tests whether the type represented by the specified Class parameter can be converted to the type represented by this Class object via an identity conversion widening primitive or widening reference conversion. See The Java Language Specification, sections 5.1.1, 5.1.2 and 5.1.4 for details.

Parameters: cls the Class to check, may be null toClass the Class to try to assign into, returns false if null

Returns: true if assignment possible

isInnerClass

public static boolean isInnerClass(Class cls)

Is the specified class an inner class or static nested class.

Parameters: cls the class to check, may be null

Returns: true if the class is an inner or static nested class, false if not or null

primitivesToWrappers

public static Class[] primitivesToWrappers(Class[] classes)

Converts the specified array of primitive Class objects to an array of its corresponding wrapper Class objects.

Parameters: classes the class array to convert, may be null or empty

Returns: an array which contains for each given class, the wrapper class or the original class if class is not a primitive. null if null input. Empty array if an empty array passed in.

Since: 2.1

primitiveToWrapper

public static Class primitiveToWrapper(Class cls)

Converts the specified primitive Class object to its corresponding wrapper Class object.

NOTE: From v2.2, this method handles Void.TYPE, returning Void.TYPE.

Parameters: cls the class to convert, may be null

Returns: the wrapper class for cls or cls if cls is not a primitive. null if null input.

Since: 2.1

toClass

public static Class[] toClass(Object[] array)

Converts an array of Object in to an array of Class objects.

This method returns null for a null input array.

Parameters: array an Object array

Returns: a Class array, null if null array input

Since: 2.4

wrappersToPrimitives

public static Class[] wrappersToPrimitives(Class[] classes)

Converts the specified array of wrapper Class objects to an array of its corresponding primitive Class objects.

This method invokes wrapperToPrimitive() for each element of the passed in array.

Parameters: classes the class array to convert, may be null or empty

Returns: an array which contains for each given class, the primitive class or null if the original class is not a wrapper class. null if null input. Empty array if an empty array passed in.

Since: 2.4

See Also: wrapperToPrimitive

wrapperToPrimitive

public static Class wrapperToPrimitive(Class cls)

Converts the specified wrapper class to its corresponding primitive class.

This method is the counter part of primitiveToWrapper(). If the passed in class is a wrapper class for a primitive type, this primitive type will be returned (e.g. Integer.TYPE for Integer.class). For other classes, or if the parameter is null, the return value is null.

Parameters: cls the class to convert, may be null

Returns: the corresponding primitive type if cls is a wrapper class, null otherwise

Since: 2.4

See Also: primitiveToWrapper

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