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.
Singleton used as a null
placeholder where
* null
has another meaning.
For example, in a HashMap
the
* {@link java.util.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.
*/ public static final Null NULL = new Null(); /** *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.
*/ public ObjectUtils() { super(); } // Defaulting //----------------------------------------------------------------------- /** *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 ** * @param object the
Object
to test, may be null
* @param defaultValue the default value to return, may be null
* @return object
if it is not null
, defaultValue otherwise
*/
public static Object defaultIfNull(Object object, Object defaultValue) {
return object != null ? object : defaultValue;
}
/**
* 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 ** * @param object1 the first object, may be
null
* @param object2 the second object, may be null
* @return true
if the values of both objects are the same
*/
public static boolean equals(Object object1, Object object2) {
if (object1 == object2) {
return true;
}
if ((object1 == null) || (object2 == null)) {
return false;
}
return object1.equals(object2);
}
/**
* Gets the hash code of an object returning zero when the
* object is null
.
* ObjectUtils.hashCode(null) = 0 * ObjectUtils.hashCode(obj) = obj.hashCode() ** * @param obj the object to obtain the hash code of, may be
null
* @return the hash code of the object, or zero if null
* @since 2.1
*/
public static int hashCode(Object obj) {
return (obj == null) ? 0 : obj.hashCode();
}
// Identity ToString
//-----------------------------------------------------------------------
/**
* 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" ** * @param object the object to create a toString for, may be *
null
* @return the default toString text, or null
if
* null
passed in
*/
public static String identityToString(Object object) {
if (object == null) {
return null;
}
StringBuffer buffer = new StringBuffer();
identityToString(buffer, object);
return buffer.toString();
}
/**
* 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") ** * @param buffer the buffer to append to * @param object the object to create a toString for * @since 2.4 */ public static void identityToString(StringBuffer buffer, Object object) { if (object == null) { throw new NullPointerException("Cannot get the toString of a null identity"); } buffer.append(object.getClass().getName()) .append('@') .append(Integer.toHexString(System.identityHashCode(object))); } // ToString //----------------------------------------------------------------------- /** *
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" ** * @see StringUtils#defaultString(String) * @see String#valueOf(Object) * @param obj the Object to
toString
, may be null
* @return the passed in Object's toString, or nullStr if null
input
* @since 2.0
*/
public static String toString(Object obj) {
return obj == null ? "" : obj.toString();
}
/**
* 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" ** * @see StringUtils#defaultString(String,String) * @see String#valueOf(Object) * @param obj the Object to
toString
, may be null
* @param nullStr the String to return if null
input, may be null
* @return the passed in Object's toString, or nullStr if null
input
* @since 2.0
*/
public static String toString(Object obj, String nullStr) {
return obj == null ? nullStr : obj.toString();
}
// Null
//-----------------------------------------------------------------------
/**
* Class used as a null placeholder where null
* has another meaning.
For example, in a HashMap
the
* {@link java.util.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.
Ensure singleton.
* * @return the singleton value */ private Object readResolve() { return ObjectUtils.NULL; } } }