iPhone XR 64GB

Design patterns - Singleton


You know how to create a perfect singleton class?

This is the way to create it..

class SingClass {
private static singClass;

public SingClass getInstance() {
if (singClass == null) {
singClass = new singClass();
}
}

private SingClass() { }
}

But, will it work always?
It works perfectly if only one thread will access it any time.

But what if multiple threads access getInstance() method simultaneously?
Use double-checking method, don't know what is double-checking?
Refer to complete explanation here..
http://www.ibm.com/developerworks/java/library/j-dcl.html


It talks about, double-checking and what are its pit falls...
Nice article...

Optimizations in OOO

What is the approximate output of the following:

private ByteArrayOutputStream baos;
private ObjectOutputStream out;
baos=new ByteArrayOutputStream(10000000);
out = new ObjectOutputStream(baos);

for(int i=0;i<1000;i++)
out.writeObject("Madhu");

System.out.println("Size = " + baos.size());

Hopefully it should print 1000*5(length of "Madhu").

But it prints a number <100.

Why .............................?????????

Because OOO has a lot of optimizations techniques. It knows that we are writing the same object again and again, so it just increases a count of the object written.

So, be careful with java....

Be careful with collection operations

Set set = new SomeSet();
short i=7;
set.add(i);
set.remove(i-1+1);
System.out.println("Size = " + set.size());

It prints 1 not 0.

Note i is short variable.
set.add(i) -> you are inserting short Object (auto boxing enters the picture).
set.remove(i-1+1) -> Here - operation promotes i to int and returns the result as int.
Finally we are trying to remove integer object (auto unboxing enters the picture).

Hence the answer is 1.

What is the output of the following program?

public class dsj {
public static void main(String args[]) {
Number ding = (true || !true) ? new Integer(7) : new Float(16);
System.out.println(ding);
}
}

It is 7.0.
? : operator is not so direct to understand.
Avoid using it, if you are mixing types such as int,float or float,long etc....
Use if...else... control structure.

శ్రీ దత్త స్తోత్ర

దత్తాత్రేయం మహాత్మానం వరదం భక్తవత్సలం
ప్రపన్నర్తిహారం వందే స్మర్త్రుగామి సనోవతు