View source for Java Programming/API/java.lang.Object

You do not have permission to edit this page, for the following reason:

Your IP address is in a range that has been blocked on all Wikimedia Foundation wikis.

The block was made by ‪EPIC‬. The reason given is Open proxy/Webhost: See the help page if you are affected.

Start of block: 11:19, 11 October 2024
Expiry of block: 11:19, 11 October 2029

Your current IP address is 52.15.129.80. The blocked range is 52.15.0.0/16.

Please include all above details in any queries you make.

If you believe you were blocked by mistake, you can find additional information and instructions in the Stewards Block Wizard.

You can view and copy the source of this page.

== java.lang.Object ==

{{java:Object}} class is the superclass of all Java classes.  All Java classes inherited from this class.  This makes it possible that we can have methods that are available in all Java classes. This simplifies things compared to C++ where this is not the case.  

{| class="wikitable"
|-
! {{java:Object}} class methods
! Description 
|-
| {{java:boolean}} equals( {{java:Object}} o );  
| Gives generic way to compare objects
|-
| {{java:Class}} getClass();
| The {{java:Class}} class gives us more information about the object
|-
| {{java:int}} hashCode();
| Returns a hash value that is used to search objects in a collection
|-
| {{java:void}} notify();
| Used in synchronizing threads
|-
| {{java:void}} notifyAll();
| Used in synchronizing threads
|-
| {{java:String}} toString();
| Can be used to convert the object to String
|-
| {{java:void}} wait();
| Used in synchronizing threads
|-
| {{java:protected}} {{java:Object}} clone() throws CloneNotSupportedException ;
| Return a new object that are exactly the same as the current object
|-
| {{java:protected}} {{java:void}} finalize() throws Throwable;
| This method is called just before an object is garbage collected
|-
|}

== equals() Method ==

* The <code>{{java:boolean}} equals( {{java:Object}} o )</code> method gives a generic way to compare objects for equality.  You need to override it, in your class. Then you can write:
 {{java:public}} {{java:boolean}} isCustomerExist( Customer newCustomer )
 {
    {{java:boolean}} isRet = {{java:false}};
    Iterator iter = _collAllCustomer.iterator();
    {{java:while}} ( iter.hasNext() )
    {
       {{java:if}} ( newCustomer.'''equals'''( (Customer) iter.next() )
       {
          // -- Customer was found ---
          isRet = {{java:true}};
       }
    }
   return isRet;
 }

Keep in mind that when you override equals(), you always need to also override hashCode() so the two methods are consistent. If two objects are equal, they must have the same hashcode.

For more information also see [[Java Programming/Comparing Objects]]

== getClass() Method ==

There is a {{java:Class}} object for each class in your program. Every array also belongs to a class that is reflected as a {{java:Class}} object that is shared by all arrays with the same element type and number of dimensions. The [[Java Programming/Primitive Types|primitive Java types]] ({{java:boolean}}, {{java:byte}}, {{java:char}}, {{java:short}}, {{java:int}}, {{java:long}}, {{java:float}}, and {{java:double}}), and the keyword {{java:void}} are also represented as {{java:Class}} objects. Class has no public constructor. Instead Class  objects are constructed automatically by the Java Virtual Machine as classes are loaded

For more information see {{java:Class}}.

The most popular use of the {{java:Class}} is to find out the object's class name during runtime.
 {{java:import}} com.yourCompany.Customer;
 ...
 Object obj = new Customer();
 ...
 System.out.println( "Name:" + obj.getClass().getName() );
The output:
 Name: com.yourCompany.Customer

== hashCode() Method ==

In most cases you should not override this method, since the default implementation of this method returns a unique number for the object. The number is used when the object is put into a [[Java Programming/Collection Classes|collection]].  Finding an object in a big collection may take a while, if objects are compared one by one sequentially.  To speed the search up, objects may be placed in a tree structure, weighted by an integer hash code.  Comparing the hash code while navigating through the tree, the number of object comparisons can be reduced.
    _______ A _____
    |              |  
 __ B__          __C__
 |     |        |     |
 D     E        F     G
 ...  ...      ...   ...
To give you a general idea of how it may work, see the above diagram. Let's say we are searching object G.  If at each 'node' of the tree we can decide which way to go, then by '''3 steps''' we reach the object G.

By constrast in a linear search:
 A --- B  ----- C  ---- C  ---- D  ---- E ---- F ---- G
We would need '''8 steps''' to reach the object G.

So the search will be faster with the tree structure. Adding a new object however, will be slower because the tree structure needs to be maintained. The place of the new object in the tree has to be found first.

== toString() Methods ==

This method can be used to convert an object to a {{java:String}}.  It is automatically used in many places to convert objects to String; for example: in PrintStream, in StringBuffer, and for the string concatenation operator when used on objects.

The default implementation returns a weird string with the class name and the hash code.

For example:
 {{java:String}} str = "This customer is " + objCust;
The <code>toString()</code> method is called on the <code>objCust</code> object.

The <code>toString()</code> method can also be used for debugging:
 {{java:public}} {{java:class}} Customer
 {
    {{java:private}} {{java:String}} _name;
    {{java:private}} {{java:String}} _address;
    {{java:private}} {{java:String}} _age;
 ...
    {{java:public}} {{java:String}} '''toString'''()
    {
        StringBuffer buf = new StringBuffer();
        buf.append( "Name   = " );  buf.append( _name );     buf.append( "\n" );
        buf.append( "Address= " );  buf.append( _address );  buf.append( "\n" );
        buf.append( "Age    = " );  buf.append( _age );      buf.append( "\n" );
     ...
        return buf.toString();
    }
 ...
 }
After that whenever in your code, you want to see what a customer object is, just call:
 System.out.println( objCustomer );

== Synchronizing Threads Methods ==
{{:Java Programming/Basic Synchronization}}

== See also: ==
* [[Java Programming/API/java.lang.Class]]
* [[Java Programming/API/java.lang.Thread]]

{{BookCat|filing=deep}}

Templates used on this page:

Java Programming/Basic Synchronization (edit)
Template:BOOKCATEGORY (view source) (protected)
Template:BookCat (view source) (protected)
Template:BookCat/core (view source) (protected)
Template:BookCat/default (view source) (protected)
Template:Evalx (view source) (protected)
Template:Java:Class (edit)
Template:Java:Object (edit)
Template:Java:String (edit)
Template:Java:api (edit)
Template:Java:boolean (edit)
Template:Java:byte (edit)
Template:Java:char (edit)
Template:Java:class (edit)
Template:Java:double (edit)
Template:Java:false (edit)
Template:Java:final (edit)
Template:Java:float (edit)
Template:Java:if (edit)
Template:Java:import (edit)
Template:Java:int (edit)
Template:Java:kw (edit)
Template:Java:long (edit)
Template:Java:private (edit)
Template:Java:protected (edit)
Template:Java:public (edit)
Template:Java:short (edit)
Template:Java:synchronized (edit)
Template:Java:true (edit)
Template:Java:void (edit)
Template:Java:while (edit)
Template:XExample (edit)
Module:TScope (view source) (protected)
Module:Wikilisp (view source) (protected)

Return to Java Programming/API/java.lang.Object.

Retrieved from "https://en.wikibooks.org/wiki/Java_Programming/API/java.lang.Object"