equals
public boolean equals(Object fld)
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
.
- equals in interface Object
- whether this Object is semantically equal to another
getDeclaringClass
public Class getDeclaringClass()
Gets the class that declared this member. This is not the class where
this method was called, or even the class where this Member object
came to life, but the class that declares the member this represents.
- getDeclaringClass in interface Member
- the class that declared this member
getModifiers
public int getModifiers()
Gets the modifiers this member uses. Use the Modifier
class to interpret the values.
- getModifiers in interface Member
- an integer representing the modifiers to this Member
getName
public String getName()
Gets the simple name of this member. This will be a valid Java
identifier, with no qualification.
- getName in interface Member
hashCode
public int hashCode()
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)
- hashCode in interface Object
- the hash code for this Object
toString
public String toString()
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())
.
- toString in interface Object
- the String representing this Object, which may be null
Copyright (C) 1998, 1999, 2000, 2001, 2003 Free Software Foundation
This file is part of libgcj.
This software is copyrighted work licensed under the terms of the
Libgcj License. Please consult the file "LIBGCJ_LICENSE" for
details.