Module prov.model

Package org.openprovenance.apache.commons.lang

Class ObjectUtils

java.lang.Object

org.openprovenance.apache.commons.lang.ObjectUtils

public class ObjectUtils
extends Object

Operations on Object.

This class tries to handle null input gracefully. An exception will generally not be thrown for a null input. Each method documents its behaviour in more detail.

#ThreadSafe#

Since:

1.0

Version:

$Id: ObjectUtils.java 1057434 2011-01-11 01:27:37Z niallp $

Author:

Apache Software Foundation, Nissim Karpenstein, Janek Bogucki, Daniel L. Rall, Gary Gregory, Mario Winterer, David J. M. Karlsen

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	ObjectUtils.Null	Class used as a null placeholder where null has another meaning.

Field Summary

Fields

Modifier and Type	Field	Description
static final ObjectUtils.Null	NULL	Singleton used as a null placeholder where null has another meaning.

Constructor Summary

Constructors

Constructor	Description
ObjectUtils()	ObjectUtils instances should NOT be constructed in standard programming.

Method Summary

Modifier and Type	Method	Description
static StringBuffer	appendIdentityToString(StringBuffer buffer, Object object)	Deprecated. The design of this method is bad - see LANG-360.
static Object	clone(Object o)	Clone an object.
static Object	cloneIfPossible(Object o)	Clone an object if possible.
static int	compare(Comparable c1, Comparable c2)	Null safe comparison of Comparables.
static int	compare(Comparable c1, Comparable c2, boolean nullGreater)	Null safe comparison of Comparables.
static Object	defaultIfNull(Object object, Object defaultValue)	Returns a default value if the object passed is null.
static boolean	equals(Object object1, Object object2)	Compares two objects for equality, where either one or both objects may be null.
static int	hashCode(Object obj)	Gets the hash code of an object returning zero when the object is null.
static String	identityToString(Object object)	Gets the toString that would be produced by Object if a class did not override toString itself.
static void	identityToString(StringBuffer buffer, Object object)	Appends the toString that would be produced by Object if a class did not override toString itself.
static Object	max(Comparable c1, Comparable c2)	Null safe comparison of Comparables.
static Object	min(Comparable c1, Comparable c2)	Null safe comparison of Comparables.
static boolean	notEqual(Object object1, Object object2)	Compares two objects for inequality, where either one or both objects may be null.
static String	toString(Object obj)	Gets the toString of an Object returning an empty string ("") if null input.
static String	toString(Object obj, String nullStr)	Gets the toString of an Object returning a specified text if null input.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

NULL

public static final ObjectUtils.Null NULL

Singleton used as a null placeholder where null has another meaning.

For example, in a HashMap the HashMap.get(Object) method returns null if the Map contains null or if there is no matching key. The Null placeholder can be used to distinguish between these two cases.

Another example is Hashtable, where null cannot be stored.

This instance is Serializable.

Constructor Details

ObjectUtils

public ObjectUtils()

ObjectUtils instances should NOT be constructed in standard programming. Instead, the class should be used as ObjectUtils.defaultIfNull("a","b");.

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

Method Details

defaultIfNull

public static Object defaultIfNull(Object object,
 Object defaultValue)

Returns a default value if the object passed is null.

 ObjectUtils.defaultIfNull(null, null)      = null
 ObjectUtils.defaultIfNull(null, "")        = ""
 ObjectUtils.defaultIfNull(null, "zz")      = "zz"
 ObjectUtils.defaultIfNull("abc", *)        = "abc"
 ObjectUtils.defaultIfNull(Boolean.TRUE, *) = Boolean.TRUE
 

Parameters:

object - the Object to test, may be null

defaultValue - the default value to return, may be null

Returns:

object if it is not null, defaultValue otherwise

equals

public static boolean equals(Object object1,
 Object object2)

Compares two objects for equality, where either one or both objects may be null.

 ObjectUtils.equals(null, null)                  = true
 ObjectUtils.equals(null, "")                    = false
 ObjectUtils.equals("", null)                    = false
 ObjectUtils.equals("", "")                      = true
 ObjectUtils.equals(Boolean.TRUE, null)          = false
 ObjectUtils.equals(Boolean.TRUE, "true")        = false
 ObjectUtils.equals(Boolean.TRUE, Boolean.TRUE)  = true
 ObjectUtils.equals(Boolean.TRUE, Boolean.FALSE) = false
 

Parameters:

object1 - the first object, may be null

object2 - the second object, may be null

Returns:

true if the values of both objects are the same

notEqual

public static boolean notEqual(Object object1,
 Object object2)

Compares two objects for inequality, where either one or both objects may be null.

 ObjectUtils.notEqual(null, null)                  = false
 ObjectUtils.notEqual(null, "")                    = true
 ObjectUtils.notEqual("", null)                    = true
 ObjectUtils.notEqual("", "")                      = false
 ObjectUtils.notEqual(Boolean.TRUE, null)          = true
 ObjectUtils.notEqual(Boolean.TRUE, "true")        = true
 ObjectUtils.notEqual(Boolean.TRUE, Boolean.TRUE)  = false
 ObjectUtils.notEqual(Boolean.TRUE, Boolean.FALSE) = true
 

Parameters:

object1 - the first object, may be null

object2 - the second object, may be null

Returns:

false if the values of both objects are the same

Since:

2.6

hashCode

public static int hashCode(Object obj)

Gets the hash code of an object returning zero when the object is null.

 ObjectUtils.hashCode(null)   = 0
 ObjectUtils.hashCode(obj)    = obj.hashCode()
 

Parameters:

obj - the object to obtain the hash code of, may be null

Returns:

the hash code of the object, or zero if null

Since:

2.1

identityToString

public static String identityToString(Object object)

Gets the toString that would be produced by Object if a class did not override toString itself. null will return null.

 ObjectUtils.identityToString(null)         = null
 ObjectUtils.identityToString("")           = "java.lang.String@1e23"
 ObjectUtils.identityToString(Boolean.TRUE) = "java.lang.Boolean@7fa"
 

Parameters:

object - the object to create a toString for, may be null

Returns:

the default toString text, or null if null passed in

identityToString

public static void identityToString(StringBuffer buffer,
 Object object)

Appends the toString that would be produced by Object if a class did not override toString itself. null will throw a NullPointerException for either of the two parameters.

 ObjectUtils.identityToString(buf, "")            = buf.append("java.lang.String@1e23"
 ObjectUtils.identityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa"
 ObjectUtils.identityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa")
 

Parameters:

buffer - the buffer to append to

object - the object to create a toString for

Since:

2.4

appendIdentityToString

public static StringBuffer appendIdentityToString(StringBuffer buffer,
 Object object)

Deprecated.

The design of this method is bad - see LANG-360. Instead, use identityToString(StringBuffer, Object).

Appends the toString that would be produced by Object if a class did not override toString itself. null will return null.

 ObjectUtils.appendIdentityToString(*, null)            = null
 ObjectUtils.appendIdentityToString(null, "")           = "java.lang.String@1e23"
 ObjectUtils.appendIdentityToString(null, Boolean.TRUE) = "java.lang.Boolean@7fa"
 ObjectUtils.appendIdentityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa")
 

Parameters:

buffer - the buffer to append to, may be null

object - the object to create a toString for, may be null

Returns:

the default toString text, or null if null passed in

Since:

2.0

toString

public static String toString(Object obj)

Gets the toString of an Object returning an empty string ("") if null input.

 ObjectUtils.toString(null)         = ""
 ObjectUtils.toString("")           = ""
 ObjectUtils.toString("bat")        = "bat"
 ObjectUtils.toString(Boolean.TRUE) = "true"
 

Parameters:

obj - the Object to toString, may be null

Returns:

the passed in Object's toString, or nullStr if null input

Since:

2.0

See Also:

• StringUtils.defaultString(String)
• String.valueOf(Object)

toString

public static String toString(Object obj,
 String nullStr)

Gets the toString of an Object returning a specified text if null input.

 ObjectUtils.toString(null, null)           = null
 ObjectUtils.toString(null, "null")         = "null"
 ObjectUtils.toString("", "null")           = ""
 ObjectUtils.toString("bat", "null")        = "bat"
 ObjectUtils.toString(Boolean.TRUE, "null") = "true"
 

Parameters:

obj - the Object to toString, may be null

nullStr - the String to return if null input, may be null

Returns:

the passed in Object's toString, or nullStr if null input

Since:

2.0

See Also:

• StringUtils.defaultString(String,String)
• String.valueOf(Object)

min

public static Object min(Comparable c1,
 Comparable c2)

Null safe comparison of Comparables.

Parameters:

c1 - the first comparable, may be null

c2 - the second comparable, may be null

Returns:

• If both objects are non-null and unequal, the lesser object.
• If both objects are non-null and equal, c1.
• If one of the comparables is null, the non-null object.
• If both the comparables are null, null is returned.

max

public static Object max(Comparable c1,
 Comparable c2)

Null safe comparison of Comparables.

Parameters:

c1 - the first comparable, may be null

c2 - the second comparable, may be null

Returns:

• If both objects are non-null and unequal, the greater object.
• If both objects are non-null and equal, c1.
• If one of the comparables is null, the non-null object.
• If both the comparables are null, null is returned.

compare

public static int compare(Comparable c1,
 Comparable c2)

Null safe comparison of Comparables. null is assumed to be less than a non-null value.

Parameters:

c1 - the first comparable, may be null

c2 - the second comparable, may be null

Returns:

a negative value if c1 < c2, zero if c1 = c2 and a positive value if c1 > c2

Since:

2.6

compare

public static int compare(Comparable c1,
 Comparable c2,
 boolean nullGreater)

Null safe comparison of Comparables.

Parameters:

c1 - the first comparable, may be null

c2 - the second comparable, may be null

nullGreater - if true null is considered greater than a Non-null value or if false null is considered less than a Non-null value

Returns:

a negative value if c1 < c2, zero if c1 = c2 and a positive value if c1 > c2

Since:

2.6

See Also:

• Comparator.compare(Object, Object)

clone

public static Object clone(Object o)

Clone an object.

Parameters:

o - the object to clone

Returns:

the clone if the object implements Cloneable otherwise null

Throws:

org.openprovenance.apache.commons.lang.exception.CloneFailedException - if the object is cloneable and the clone operation fails

Since:

2.6

cloneIfPossible

public static Object cloneIfPossible(Object o)

Clone an object if possible. This method is similar to clone(Object), but will return the provided instance as the return value instead of null if the instance is not cloneable. This is more convenient if the caller uses different implementations (e.g. of a service) and some of the implementations do not allow concurrent processing or have state. In such cases the implementation can simply provide a proper clone implementation and the caller's code does not have to change.

Parameters:

o - the object to clone

Returns:

the clone if the object implements Cloneable otherwise the object itself

Throws:

org.openprovenance.apache.commons.lang.exception.CloneFailedException - if the object is cloneable and the clone operation fails

Since:

2.6