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#
* @author Apache Software Foundation * @author Nissim Karpenstein * @author Janek Bogucki * @author Daniel L. Rall * @author Gary Gregory * @author Mario Winterer * @author David J. M. Karlsen * @since 1.0 * */ //@Immutable public class ObjectUtils { /** *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);
}
/**
* 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
*
*
* @param object1 the first object, may be null
* @param object2 the second object, may be null
* @return false if the values of both objects are the same
* @since 2.6
*/
public static boolean notEqual(Object object1, Object object2) {
return ObjectUtils.equals(object1, object2) == false;
}
/**
* 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)));
}
/**
* 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")
*
*
* @param buffer the buffer to append to, may be null
* @param object the object to create a toString for, may be null
* @return the default toString text, or null if
* null passed in
* @since 2.0
* @deprecated The design of this method is bad - see LANG-360. Instead, use identityToString(StringBuffer, Object).
*/
public static StringBuffer appendIdentityToString(StringBuffer buffer, Object object) {
if (object == null) {
return null;
}
if (buffer == null) {
buffer = new StringBuffer();
}
return 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();
}
// Min/Max
//-----------------------------------------------------------------------
/**
* Null safe comparison of Comparables.
*
* @param c1 the first comparable, may be null
* @param c2 the second comparable, may be null
* @return
* null is considered greater
* than a Non-null value or if false null is
* considered less than a Non-null value
* @return a negative value if c1 < c2, zero if c1 = c2
* and a positive value if c1 > c2
* @see java.util.Comparator#compare(Object, Object)
* @since 2.6
*/
public static int compare(Comparable c1, Comparable c2, boolean nullGreater) {
if (c1 == c2) {
return 0;
} else if (c1 == null) {
return (nullGreater ? 1 : -1);
} else if (c2 == null) {
return (nullGreater ? -1 : 1);
}
return c1.compareTo(c2);
}
/**
* Clone an object.
*
* @param o the object to clone
* @return the clone if the object implements {@link Cloneable} otherwise null
* @throws CloneFailedException if the object is cloneable and the clone operation fails
* @since 2.6
*/
public static Object clone(final Object o) {
if (o instanceof Cloneable) {
final Object result;
if (o.getClass().isArray()) {
final Class componentType = o.getClass().getComponentType();
if (!componentType.isPrimitive()) {
result = ((Object[])o).clone();
} else {
int length = Array.getLength(o);
result = Array.newInstance(componentType, length);
while (length-- > 0) {
Array.set(result, length, Array.get(o, length));
}
}
} else {
try {
result = MethodUtils.invokeMethod(o, "clone", null);
} catch (final NoSuchMethodException e) {
throw new CloneFailedException("Cloneable type "
+ o.getClass().getName()
+ " has no clone method", e);
} catch (final IllegalAccessException e) {
throw new CloneFailedException("Cannot clone Cloneable type "
+ o.getClass().getName(), e);
} catch (final InvocationTargetException e) {
throw new CloneFailedException("Exception cloning Cloneable type "
+ o.getClass().getName(), e.getTargetException());
}
}
return result;
}
return null;
}
/**
* Clone an object if possible. This method is similar to {@link #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.
*
* @param o the object to clone
* @return the clone if the object implements {@link Cloneable} otherwise the object itself
* @throws CloneFailedException if the object is cloneable and the clone operation fails
* @since 2.6
*/
public static Object cloneIfPossible(final Object o) {
final Object clone = clone(o);
return clone == null ? o : clone;
}
// 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; } } }