This method may be called to create a new copy of the
Object. The typical behavior is as follows:
o == o.clone() is false
o.getClass() == o.clone().getClass()
is true
o.equals(o) is true
However, these are not strict requirements, and may
be violated if necessary. Of the three requirements, the
last is the most commonly violated, particularly if the
subclass does not override Object.equals(Object).
If the Object you call clone() on does not implement
Cloneable (which is a placeholder interface), then
a CloneNotSupportedException is thrown. Notice that
Object does not implement Cloneable; this method exists
as a convenience for subclasses that do.
Object's implementation of clone allocates space for the
new Object using the correct class, without calling any
constructors, and then fills in all of the new field values
with the old field values. Thus, it is a shallow copy.
However, subclasses are permitted to make a deep copy.
All array types implement Cloneable, and override
this method as follows (it should never fail):
public Object clone()
{
try
{
super.clone();
}
catch (CloneNotSupportedException e)
{
throw new InternalError(e.getMessage());
}
}
Determine whether this Object is semantically equal
to another Object.
There are some fairly strict requirements on this
method which subclasses must follow:
It must be transitive. If a.equals(b) and
b.equals(c), then a.equals(c)
must be true as well.
It must be symmetric. a.equals(b) and
b.equals(a) must have the same value.
It must be reflexive. a.equals(a) must
always be true.
It must be consistent. Whichever value a.equals(b)
returns on the first invocation must be the value
returned on all later invocations.
a.equals(null) must be false.
It must be consistent with hashCode(). That is,
a.equals(b) must imply
a.hashCode() == b.hashCode().
The reverse is not true; two objects that are not
equal may have the same hashcode, but that has
the potential to harm hashing performance.
This is typically overridden to throw a ClassCastException
if the argument is not comparable to the class performing
the comparison, but that is not a requirement. It is legal
for a.equals(b) to be true even though
a.getClass() != b.getClass(). Also, it
is typical to never cause a NullPointerException.
In general, the Collections API (java.util) use the
equals method rather than the ==
operator to compare objects. However, IdentityHashMap
is an exception to this rule, for its own good reasons.
The default implementation returns this == o.
Get a value that represents this Object, as uniquely as
possible within the confines of an int.
There are some requirements on this method which
subclasses must follow:
Semantic equality implies identical hashcodes. In other
words, if a.equals(b) is true, then
a.hashCode() == b.hashCode() must be as well.
However, the reverse is not necessarily true, and two
objects may have the same hashcode without being equal.
It must be consistent. Whichever value o.hashCode()
returns on the first invocation must be the value
returned on all later invocations as long as the object
exists. Notice, however, that the result of hashCode may
change between separate executions of a Virtual Machine,
because it is not invoked on the same object.
Notice that since hashCode is used in
Hashtable and other hashing classes,
a poor implementation will degrade the performance of hashing
(so don't blindly implement it as returning a constant!). Also,
if calculating the hash is time-consuming, a class may consider
caching the results.
The default implementation returns
System.identityHashCode(this)
Convert this Object to a human-readable String.
There are no limits placed on how long this String
should be or what it should contain. We suggest you
make it as intuitive as possible to be able to place
it into System.out.println()
and such.
It is typical, but not required, to ensure that this method
never completes abruptly with a RuntimeException.
This method will be called when performing string
concatenation with this object. If the result is
null, string concatenation will instead
use "null".
The default implementation returns
getClass().getName() + "@" +
Integer.toHexString(hashCode()).
BasicAttribute.java --
Copyright (C) 2000, 2001, 2004, 2006 Free Software Foundation, Inc.
This file is part of GNU Classpath.
GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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