org.apache.commons.lang
Class ObjectUtils

java.lang.Object
  extended byorg.apache.commons.lang.ObjectUtils

public class ObjectUtils
extends java.lang.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.

Since:
1.0
Version:
$Id: ObjectUtils.java 594336 2007-11-12 22:54:02Z bayard $
Author:
Nissim Karpenstein, Janek Bogucki, Daniel L. Rall, Stephen Colebourne, Gary Gregory, Mario Winterer, David J. M. Karlsen

Nested Class Summary
static class ObjectUtils.Null
          Class used as a null placeholder where null has another meaning.
 
Field Summary
static ObjectUtils.Null NULL
          Singleton used as a null placeholder where null has another meaning.
 
Constructor Summary
ObjectUtils()
          ObjectUtils instances should NOT be constructed in standard programming.
 
Method Summary
static java.lang.StringBuffer appendIdentityToString(java.lang.StringBuffer buffer, java.lang.Object object)
          Deprecated. The design of this method is bad - see LANG-360. Instead, use identityToString(StringBuffer, Object).
static java.lang.Object defaultIfNull(java.lang.Object object, java.lang.Object defaultValue)
          Returns a default value if the object passed is null.
static boolean equals(java.lang.Object object1, java.lang.Object object2)
          Compares two objects for equality, where either one or both objects may be null.
static int hashCode(java.lang.Object obj)
          Gets the hash code of an object returning zero when the object is null.
static java.lang.String identityToString(java.lang.Object object)
          Gets the toString that would be produced by Object if a class did not override toString itself.
static void identityToString(java.lang.StringBuffer buffer, java.lang.Object object)
          Appends the toString that would be produced by Object if a class did not override toString itself.
static java.lang.Object max(java.lang.Comparable c1, java.lang.Comparable c2)
          Null safe comparison of Comparables.
static java.lang.Object min(java.lang.Comparable c1, java.lang.Comparable c2)
          Null safe comparison of Comparables.
static java.lang.String toString(java.lang.Object obj)
          Gets the toString of an Object returning an empty string ("") if null input.
static java.lang.String toString(java.lang.Object obj, java.lang.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 Detail

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(java.lang.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 Detail

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 Detail

defaultIfNull

public static java.lang.Object defaultIfNull(java.lang.Object object,
                                             java.lang.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(java.lang.Object object1,
                             java.lang.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

hashCode

public static int hashCode(java.lang.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 java.lang.String identityToString(java.lang.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(java.lang.StringBuffer buffer,
                                    java.lang.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 java.lang.StringBuffer appendIdentityToString(java.lang.StringBuffer buffer,
                                                            java.lang.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 java.lang.String toString(java.lang.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 java.lang.String toString(java.lang.Object obj,
                                        java.lang.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 java.lang.Object min(java.lang.Comparable c1,
                                   java.lang.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 java.lang.Object max(java.lang.Comparable c1,
                                   java.lang.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.


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