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java.lang.Object
- See Also:
- Top Examples, Source Code,
Class
protected Object clone()
throws CloneNotSupportedException- See Also:
Cloneable
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[1524]DecimalFormat
By ednava58 { at } yahoo { dot } com on 2005/08/28 17:15:11 Rate
DecimalFormat percent = new DecimalFormat ( "0%" ) ;[1754]How many ways can we create an Object?
By Anonymous on 2006/05/04 15:49:45 Rate
I can think of 6 possible ways:
1. call new ( ) which calls a constructor of a class
2. In a singleton class, call method named getInstance ( ) which returns a reference to a new single object the first time it is called. But, under the hood, it still calls the private constructor. Singleton is a pattern, meaning there is only one instance of the object. [ NB: on subsequent calls, getInstance ( ) returns the same singleton object, so the object is no longer "a newly created object". ]
3. Deserialize a object from data that is stored within a byte [ ] array, stored within a disk file, or has been received from some network prototocol ( for example, from a socket that uses TCP/IP protocol. ) .
4. Call a method which returns a created object. ( This might not be a fair answer, since the called method has to do 1, 2, or 3 internally ) .
5. Use reflection: http://javaalmanac.com/egs/java.lang.reflect/UseConstructor.html
6. Use dynamic proxy object: http://java.sun.com/j2se/1.3/docs/guide/reflection/proxy.html
public boolean equals(Object obj) - See Also:
Hashtable, hashCode()
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[385]Two equals objects have matching hashCode()s as well
By Ry4an Brase on 2003/09/09 03:45:17 Rate
// The key is to make sure that two equals objects have matching
// hashCode ( ) s as well
public boolean equals ( Object o ) {
if ( o == null || ! ( o instanceof ThisClass ) ) {
return false;
}
if ( aField != o.aField ) { // and so on
return false;
}
// ASSERT o.hashCode ( ) == hashCode ( )
return true;
} [1694]Implementation of equals for Collections and Objects arrays.
By prasuvalli_i { at } yahoo { dot } co { dot } in on 2006/01/05 16:05:28 Rate
public static boolean equals ( Collection c1, Collection c2 ) {
boolean result = false;
if ( c1.getClass ( ) != c2.getClass ( ) )
return false;
Object [ ] o1 = ( Object [ ] ) c1.toArray ( new Object [ c1.size ( ) ] ) ;
Object [ ] o2 = ( Object [ ] ) c2.toArray ( new Object [ c2.size ( ) ] ) ;
result = equals ( o1, o2 ) ;
return result;
}
public static boolean equals ( Object [ ] c1, Object [ ] c2 ) {
if ( c1.length != c2.length ) { // could drop this check for fixed-length keys
return false;
}
if ( c1 == c2 )
return true;
if ( null == c1 || null == c2 )
return false;
for ( int i = 0, len = c1.length; i < len; i++ ) { // could skip invariants
if ( !equals ( c1 [ i ] ,c2 [ i ] ) ) {
return false;
}
}
return true;
}
protected void finalize()
throws Throwable- Geek's Notes:
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[1901]Avoid Finalizers
By Anonymous on 2007/07/05 08:24:12 Rate
Finalizers are unpredictable, often dangerous, and generally unnecessary. ... Finalizers have a few valid uses, which we'll cover later in this item, but as a rule of thumb, finalizers should be avoided. Further, System.gc and System.runFinalization may increase the odds of finalizers getting executed, but they don't guarantee it.[1902]A class to make the finalizer thread max priority to make sure stuff gets finalized
By Anonymous on 2007/07/05 08:35:34 Rate
I suffered lots of OutOfMemory. What I finally figured out was that all the memory was sitting around waiting to be finalized. I had many threads creating garbage that needed to be finalized ( on a multi-processor server ) , and apparently on a single "low-priority" finalizer thread trying to clean up after the fact. My workaround consists of this code ( which I call each time my servlet is invoked ) :
public static class finalizer_max {
public void finalize ( ) {
Thread.currentThread ( ) .setPriority ( Thread.MAX_PRIORITY ) ;
}
}
private static boolean finalize_fixed = false;
private synchronized static void fixFinalize ( ) {
if ( !finalize_fixed ) {
// Initialize the finalizer thread. We need to bump up the priority
// to make sure stuff gets finalized
finalizer_fixed = true;
new finalizer_max ( ) ;
System.gc ( ) ;
System.runFinalization ( ) ;
}
}
public final Class<? extends Object> getClass() - Geek's Notes:
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[310]Invoke a method on the Object class
By Anonymous on 2003/07/22 06:50:55 Rate
import java.lang.*;
import java.lang.reflect.* ;
public class try1 {
public static void main ( String [ ] args ) throws Exception {
try1 t = new try1 ( ) ;
t.processActions ( t ) ;
}
public void processActions ( Object obj ) throws Exception {
Method m = obj.getClass ( ) .getMethod ( "systemOut",null ) ;
m.invoke ( obj, new Object [ ] { } ) ;
}
public void systemOut ( ) {
System.out.println ( "Hello" ) ;
}
} [962]Class without instances
By Anonymous on 2004/10/01 14:36:02 Rate
There's a getClass ( ) method for getting the Class object of a given object, but this means you have to have an instance of the object first. But what if you just want to compare a Class variable to an existing class ( like instanceof but without having an instance ) or you want the Class object of a static class ( i.e. a class without instances ) ?
There is a special language construct for getting the class object of a given class: < classname > .class. So, if we want the class object of, say, System:
Class systemclass = System.class;
The notation suggests that class is actually a public static field of Object, but this is not so. If you want the class field of an object, use getClass ( ) .
public int hashCode() - See Also:
Hashtable, equals(java.lang.Object)
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public final void notify() - See Also:
wait(), notifyAll(), IllegalMonitorStateException
- Geek's Notes:
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public final void notifyAll() - See Also:
wait(), notify(), IllegalMonitorStateException
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[1402]Difference between notify() and notifyAll()
By shamaz on 2005/04/26 11:11:59 Rate
this class shows the difference between notify ( ) and notifyAll ( )
public class Test
{
public void go ( )
{
Test test = new Test ( ) ;
( new Thread1 ( test ) ) .start ( ) ;
( new Thread2 ( test ) ) .start ( ) ;
( new Notifier ( test ) ) .start ( ) ;
}
class Thread1 extends Thread
{
Test t;
Thread1 ( Test t )
{
this.t = t;
}
public void run ( )
{
try
{
t.wait ( 5000 ) ;
}
catch ( InterruptedException ie ) { }
System.out.println ( "thread 1" ) ;
}
}
class Thread2 extends Thread
{
Test t;
Thread2 ( Test t )
{
this.t = t;
}
public void run ( )
{
try
{
t.wait ( 5000 ) ;
}
catch ( InterruptedException ie ) { }
System.out.println ( "thread 2" ) ;
}
}
class Notifier extends Thread
{
Test t;
Notifier ( Test t )
{
this.t = t;
}
public void run ( )
{
synchronized ( t )
{
t.notify ( ) ;
}
}
}
}
If you call the go ( ) method, then only one thread will awake.
If you put t.notifyAll ( ) , instead of t.notify ( ) then the 2 threads will awake[1434]wait() methode need a synchronized block
By Anonymous on 2005/05/19 04:24:53 Rate
class Test2
{
int a =0;
public static void main ( String [ ] args ) {
new Test2 ( ) .go ( ) ;
}
public void go ( )
{
Test2 test = new Test2 ( ) ;
( new Thread1 ( test ) ) .start ( ) ;
( new Thread2 ( test ) ) .start ( ) ;
( new Notifier ( test ) ) .start ( ) ;
}
class Thread1 extends Thread
{
Test2 t;
Thread1 ( Test2 t )
{
this.t = t;
}
public void run ( )
{
synchronized ( t ) {
try
{
t.wait ( 5000 ) ;
t.wait ( 5000 ) ;
}
catch ( InterruptedException ie ) { }
t.a=1;
System.out.println ( "thread 1"+t.a ) ;
}
}
}
class Thread2 extends Thread
{
Test2 t;
Thread2 ( Test2 t )
{
this.t = t;
}
public void run ( )
{
synchronized ( t ) {
try
{
t.wait ( 5000 ) ;
}
catch ( InterruptedException ie ) { }
t.a=2;
System.out.println ( "thread 2"+t.a ) ;
}
}
}
class Notifier extends Thread
{
Test2 t;
Notifier ( Test2 t )
{
synchronized ( t ) {
this.t = t;
}
}
public void run ( )
{
synchronized ( t )
{
t.notifyAll ( ) ;
}
}
}
}
Hello just to say that wait ( ) methode need a synchronized block.
public Object() - Geek's Notes:
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[177]Fine-grained locking
By Anonymous on 2003/03/14 08:54:54 Rate
//The explicit block is better than the standard implementation ( synchronizing all methods )
//because both methods can run concurrently, which reduces locking costs and
//increases scalability. The caveat is that you can't have two threads invoking
//the same method on the same object, which is the consistency we want to enforce.
import java.util.Date;
public class Person1
{
private String name, surname;
private Date birth, death;
private final Object nameLock =
new Object ( ) , dateLock = new Object ( ) ;
public void setNames (
String name, String surname )
{
synchronized ( nameLock )
{
this.name = name;
this.surname = surname;
}
}
public void setDates ( Date birth, Date death )
{
synchronized ( dateLock )
{
this.birth = birth;
this.death = death;
}
}
}
public String toString() - Geek's Notes:
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[1486]Manipulate Array element through reflection
By Sreenivas on 2005/07/17 10:00:05 Rate
public final class Tex3 {
private boolean flag=false;
public void sample ( ) {
Inner in1=new Inner ( ) ;
System.out.println ( "Sample \t"+in1 ) ;
}
public static void main ( String a [ ] ) {
Tex3 e1=new Tex3 ( ) ;
e1.sample ( ) ;
}
}
class Inner {
private boolean flag1=false;
int i=555;
public String toString ( ) {
if ( flag1 )
return "true"+i;
else
return "false"+i;
}
}
public final void wait()
throws InterruptedException- See Also:
notifyAll(), notify(), IllegalMonitorStateException
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[489]Sync block
By Anonymous on 2003/11/04 10:04:17 Rate
java.lang.Object sync = new java.lang.Object ( ) ;
synchronized ( sync ) {
sync.wait ( ) ;
}
public final void wait(long timeout)
throws InterruptedException- See Also:
notifyAll(), notify(), IllegalMonitorStateException, IllegalArgumentException, interrupted
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[1542]Difference between sleep and wait
By Anonymous on 2005/09/22 15:32:07 Rate
Unlike sleep ( 1000 ) which puts thread aside for exactly one second. wait ( 1000 ) causes a wait of up to one second. A thread could stop waiting earlier if it receives the notify ( ) or notifyAll ( ) call.
public final void wait(long timeout,
int nanos)
throws InterruptedException- See Also:
- IllegalMonitorStateException, IllegalArgumentException,
wait(long), notifyAll(), notify()
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- Description Add your codes or notes Search More Java Examples
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