Class Object
- java.lang.Object
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public class Object
The root class of the Java class hierarchy. All non-primitive types (including arrays) inherit either directly or indirectly from this class.Object
provides some fundamental methods for accessing theClass
of an object, getting itshashCode()
, or checking whether one objectequals(Object)
another. ThetoString()
method can be used to convert an object reference into a printable string and is often overridden in subclasses.The
#wait()
and#notify()
methods provide a foundation for synchronization, acquiring and releasing an internal monitor associated with eachObject
.
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Constructor Summary
Constructors Constructor and Description Object()
Constructs a new instance ofObject
.
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Method Summary
Methods Modifier and Type Method and Description boolean
equals(Object o)
Compares this instance with the specified object and indicates if they are equal.Class<? extends Object>
getClass()
Returns the unique instance ofClass
which represents this object's class.int
hashCode()
Returns an integer hash code for this object.String
toString()
Returns a string containing a concise, human-readable description of this object.
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Method Detail
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equals
public boolean equals(Object o)
Compares this instance with the specified object and indicates if they are equal. In order to be equal,o
must represent the same object as this instance using a class-specific comparison. The general contract is that this comparison should be both transitive and reflexive.The implementation in
Object
returnstrue
only ifo
is the exact same object as the receiver (using the == operator for comparison). Subclasses often implementequals(Object)
so that it takes into account the two object's types and states.The general contract for the
equals(Object)
andhashCode()
methods is that ifequals
returnstrue
for any two objects, thenhashCode()
must return the same value for these objects. This means that subclasses ofObject
usually override either both methods or none of them.- Parameters:
o
- the object to compare this instance with.- Returns:
true
if the specified object is equal to thisObject
;false
otherwise.- See Also:
hashCode()
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getClass
public final Class<? extends Object> getClass()
Returns the unique instance ofClass
which represents this object's class. Note thatgetClass()
is a special case in that it actually returnsClass<? extends Foo>
whereFoo
is the erasure of the type of expressiongetClass()
was called upon.As an example, the following code actually compiles, although one might think it shouldn't:
List
l = new ArrayList (); Class extends List> c = l.getClass(); - Returns:
- this object's
Class
instance.
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hashCode
public int hashCode()
Returns an integer hash code for this object. By contract, any two objects for whichequals(Object)
returnstrue
must return the same hash code value. This means that subclasses ofObject
usually override both methods or neither method.- Returns:
- this object's hash code.
- See Also:
equals(java.lang.Object)
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toString
public String toString()
Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation simply concatenates the class name, the '@' sign and a hexadecimal representation of the object'shashCode()
, that is, it is equivalent to the following expression:getClass().getName() + '@' + Integer.toHexString(hashCode())
- Returns:
- a printable representation of this object.
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