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§1.12 Class Object
public class java.lang.Object
{
// Constructors
public Object(); §1.12.1
// Methods
protected Object clone(); §1.12.2
public boolean equals(Object obj); §1.12.3
protected void finalize(); §1.12.4
public final Class getClass(); §1.12.5
public int hashCode(); §1.12.6
public final void notify(); §1.12.7
public final void notifyAll(); §1.12.8
public String toString(); §1.12.9
public final void wait(); §1.12.10
public final void wait(long timeout); §1.12.11
public final void wait(long timeout, int nanos); §1.12.12
}
Class Object is the root of the class hierarchy. Every class has Object as a superclass. parent.
All objects, including arrays, implement the methods of this class.
Object
public Object()
- Allocates a new instance of class Object.
clone
protected Object clone()
throws CloneNotSupportedException
- The clone method of class Object creates a new object of the same class as
this object. It then initializes each of the new object's fields by assigning it
the same value as the corresponding field in this object. No constructor is
called.
- The clone method of class Object will only clone an object whose class indicates that it is willing for its instances to be cloned. A class indicates that
its instances can be cloned by declaring that it implements the Cloneable
(I-§1.22) interface.
- Returns:
- a clone of this instance.
- Throws
- OutOfMemoryError (I-§1.57)
- If there is not enough memory.
- Throws
- CloneNotSupportedException (I-§1.29)
- The object's class does not support the Cloneable interface. Subclasses
that override the clone method can also throw this exception to indicate
that an instance cannot be cloned.
equals
public boolean equals(Object obj)
- Indicates whether some other object is "equal to" this one.
- The equals method implements an equivalence relation:
- The equals method for class Object implements the most discriminating
possible equivalence relation on objects; that is, for any reference values x
and y, this method returns true if and only if x and y refer to the same object
(x==y has the value true).
- Parameters:
obj
-
the reference object with which to compare
- Returns:
- true if this object is the same as the obj argument; false otherwise.
- See Also:
- Hashtable (I-§3.4)
- hashCode (§1.12.6).
finalize
protected void finalize()
throws Throwable
- The finalize method is called by the garbage collector on an object when
garbage collection determines that there are no more references to the
object. A subclass overrides the finalize method in order to dispose of system resources or to perform other cleanup.
- Any exception thrown by the finalize method causes the finalization of this
object to be halted, but is otherwise ignored.
- The finalize method in Object does nothing.
getClass
public final Class getClass()
- Determines the run-time class of an object.
- Returns:
- the object of type Class (I-§1.3) that represents the run-time class of
the object.
hashCode
public int hashCode()
- Calculates a hash code value for the object. This method is supported for
the benefit of hash tables such as those provided by java.util.Hashtable (I-§3.4).
- The general contract of hashCode is:
- Returns:
- a hash code value for this object.
notify
public final void notify()
- Wakes up a single thread that is waiting on this object's monitor. A thread
waits on an object's monitor by calling one of the wait methods
(I-§1.12.10-§1.12.12).
- This method should only be called by a thread that is the owner of this
object's monitor. A thread becomes the owner of the object's monitor in
one of three ways:
- Only one thread at a time can only an object's monitor.
- Throws
- IllegalMonitorStateException (I-§1.33)
- If the current thread is not the owner of this object's monitor.
- See Also:
- notifyAll (I-§1.12.8).
notifyAll
public final void notifyAll()
- Wakes up all threads that are waiting on this object's monitor. A thread
waits on an object's monitor by calling one of the wait methods
(I-§1.12.10-§1.12.12).
- This method should only be called by a thread that is the owner of this
object's monitor. See the notify method (I-§1.12.7) for a description of the
ways in which a thread can become the owner of a monitor.
- Throws
- IllegalMonitorStateException (I-§1.33)
- If the current thread is not the owner of this object's monitor.
toString
public String toString()
- Creates a string representation of the object. In general, the toString method
returns a string that "textually represents" this object. The result should be
a concise but informative representation that is easy for a person to read.
- The toString method for class Object returns a string consisting of the name
of the class of which the object is an instance, the at-sign character `@',
and the unsigned hexadecimal representation of the hash code of the
object1.
- Returns:
- A string representation of the object.
wait
public final void wait()
throws InterruptedException
- Waits to be notified by another thread of a change in this object.
- The current thread must own this object's monitor. The thread releases
ownership of this monitor and waits until another thread notifies threads
waiting on this object's monitor to wake up either through a call to the
notify method (I-§1.12.7) or the notifyAll method(I-§1.12.7). The thread
then waits until it can re-obtain ownership of the monitor and resumes execution.
- This method should only be called by a thread that is the owner of this
object's monitor. See the notify method (I-§1.12.7) for a description of the
ways in which a thread can become the owner of a monitor.
- Throws
- IllegalMonitorStateException (I-§1.33)
- If the current thread is not the owner of the object's monitor.
- Throws
- InterruptedException (I-§1.37)
- Another thread has interrupted this thread.
wait
public final void wait(long timeout)
throws InterruptedException
- Waits to be notified by another thread of a change in this object.
- The current thread must own this object's monitor. The thread releases
ownership of this monitor and waits until either of the following two conditions has occurred:
- The thread then waits until it can re-obtain ownership of the monitor and
resumes execution
- This method should only be called by a thread that is the owner of this
object's monitor. See the notify method (I-§1.12.7) for a description of the
ways in which a thread can become the owner of a monitor.
- Parameters:
timeout
-
the maximum time to wait in milliseconds
- Throws
- IllegalMonitorStateException (I-§1.33)
- If the current thread is not the owner of the object's monitor.
- Throws
- InterruptedException (I-§1.37)
Another thread has interrupted this thread.
wait
public final void wait(long timeout, int nanos)
throws InterruptedException
- Waits to be notified by another thread of a change in this object.
- This method is similar to the wait method (I-§1.12.11) of one argument,
but it allows finer control over the amount of time to wait for a notification
before giving up.
- The current thread must own this object's monitor. The thread releases
ownership of this monitor and waits until either of the following two conditions has occurred:
- The thread then waits until it can re-obtain ownership of the monitor and
resumes execution
- This method should only be called by a thread that is the owner of this
object's monitor. See the notify method (I-§1.12.7) for a description of the
ways in which a thread can become the owner of a monitor.
- Parameters:
timeout
-
the maximum time to wait in milliseconds
nano
-
additional time, in nanoseconds range 0-999999
- Throws
- IllegalMonitorStateException (I-§1.33)
- If the current thread is not the owner of this object's monitor.
- Throws
- InterruptedException (I-§1.37)
- Another thread has interrupted this thread.
1
In Java 1.0, the hexidecimal string printed after the `@' is based on the hash code
value, but may not be the actual hash code value.
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Java API Document (HTML generated by dkramer on April 22, 1996)
Copyright © 1996 Sun Microsystems, Inc.
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Please send any comments or corrections to doug.kramer@sun.com