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.

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

For example, in a HashMap the 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 ObjectUtils() 
{
        super();
}

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 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)));
}

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")

 public static Object defaultIfNull(Object object,
    Object defaultValue) 
{
        return object != null ? 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

 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 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

 public static int hashCode(Object obj) 
{
        return (obj == null) ? 0 : obj.hashCode();
}

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

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

 public static String identityToString(Object object) 
{
        if (object == null) {
            return null;
        }
        StringBuffer buffer = new StringBuffer();
        identityToString(buffer, object);
        return buffer.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"

 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 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")

 public static Object max(Comparable c1,
    Comparable c2) 
{
        if (c1 != null && c2 != null) {
            return c1.compareTo(c2)  >= 0 ? c1 : c2;
        } else {
            return c1 != null ? c1 : c2;
        }
}

Null safe comparison of Comparables.

 public static Object min(Comparable c1,
    Comparable c2) 
{
        if (c1 != null && c2 != null) {
            return c1.compareTo(c2) <  1 ? c1 : c2;
        } else {
            return c1 != null ? c1 : c2;
        }
}

Null safe comparison of Comparables.

 public static String toString(Object obj) 
{
        return obj == null ? "" : obj.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"

 public static String toString(Object obj,
    String nullStr) 
{
        return obj == null ? nullStr : 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"