Java : Static Methods and Static Blocks Output

Question

This is the source code for demonstrating a static block and static method.

class StaticDemo
{
static int count=10;

 StaticDemo(){
 count++;
 }
 static void display(){
  System.out.println(count);
 }

 static{
  System.out.println("Static Block written Before Main");
 }

 public static void main(String args[]){
     StaticDemo t1=new StaticDemo();
     StaticDemo t2=new StaticDemo();

     StaticDemo.display();
     t2.display();

  }
  static{
     System.out.println("Static Block written After Main");
  }
 }

I expect an output of

Static Block written Before Main 
Static Block written After Main 
11
12

whereas I get an output of

Static Block written Before Main 
Static Block written After Main 
12
12

I understand that the static blocks are the first set of code to be executed and hence the order of the first 2 statements. However, when the JVM creates the object t1 of StaticDemo class, doesn't the value of count get incremented to 11 ( 10+1 )? When does the initialization/increment actually occur in the program? Thank you!

What do you expect? It works just as should.

BobTheBuilder
– BobTheBuilder

2013-04-24 11:19:16 +00:00
Commented Apr 24, 2013 at 11:19 — BobTheBuilder
– BobTheBuilder, Commented Apr 24, 2013 at 11:19

Peter Lawrey · Accepted Answer · 2013-04-24 11:19:47Z

4

The increment occurs in the constructor. You call the constructor twice before displaying the counter so it is incremented twice. If you place the display() between the two constructor calls you will see 11 12 as you expect.

BTW You can see all this by stepping through the code in your debugger.

answered Apr 24, 2013 at 11:19

Peter Lawrey

535k83 gold badges770 silver badges1.2k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Aleks G · Accepted Answer · 2013-04-24 11:21:16Z

3

The output is explained by the order of the statements in your main method:

 StaticDemo t1=new StaticDemo();       //this increments count to 11
 StaticDemo t2=new StaticDemo();       //this increments count to 12

 StaticDemo.display();                 //this outputs 12
 t2.display();                         //this outputs 12

Essentially, you're incrementing twice, then outputting twice - hence the result.

answered Apr 24, 2013 at 11:21

Aleks G

57.5k34 gold badges180 silver badges280 bronze badges

Comments

MD Sayem Ahmed · Accepted Answer · 2013-04-24 11:19:29Z

2

Look at your constructor -

StaticDemo(){
    count++;
}

You are incrementing the static variable every time you create an object. You've created two objects here, so it will get incremented by two. This explains why you are getting 12 two times.

To get your "expected" output -

public static void main(String args[]){
    StaticDemo t1=new StaticDemo();    // count got incremented, now contains 11
    StaticDemo.display();    // will print 11

    StaticDemo t2=new StaticDemo();  // again count got incremented
    t2.display();    // will print 12
}

I hope this clears up the actual output for you.

answered Apr 24, 2013 at 11:19

MD Sayem Ahmed

29.3k27 gold badges115 silver badges183 bronze badges

Comments

Danny. · Accepted Answer · 2013-04-24 11:20:40Z

1

 public static void main(String args[]){
     StaticDemo t1=new StaticDemo();
     StaticDemo.display();
     StaticDemo t2=new StaticDemo();
     t2.display();

  }

Output:

Static Block written Before Main Static Block written After Main 11 12

edit:// problem is you call display(), after you called the constructer 2 times. because display() using the same value you get each time 12

edit2:// to late sry

answered Apr 24, 2013 at 11:20

Danny.

3631 gold badge4 silver badges23 bronze badges

Comments

Manish · Accepted Answer · 2013-04-24 11:22:58Z

0

See below:

public static void main(String args[]){
             //Initially value of count is 10
             StaticDemo t1=new StaticDemo(); //here it becomes 11
             StaticDemo t2=new StaticDemo(); //here it becomes 12

             StaticDemo.display(); //Now you are printing, it will print 12
             t2.display(); //The value has not changed, so again 12

          }

If you re-write the block as:

 public static void main(String args[]){

             StaticDemo t1=new StaticDemo(); 
             StaticDemo.display(); 
             StaticDemo t2=new StaticDemo(); 
              t2.display(); 

          }

Then you should see the output as 11, 12

answered Apr 24, 2013 at 11:22

Manish

3,9782 gold badges34 silver badges46 bronze badges

Comments

Srinivas · Accepted Answer · 2013-04-24 11:28:39Z

0

@user2315188..

Your are creating t1 and t2 objects so the no-argument constructor call 2 times,the first time count values is 11 and second time the count become 12 so you are getting output 12,12

     StaticDemo t1=new StaticDemo();
     StaticDemo t2=new StaticDemo();

answered Apr 24, 2013 at 11:28

Srinivas

1475 bronze badges

Collectives™ on Stack Overflow

Java : Static Methods and Static Blocks Output

6 Answers 6

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

6 Answers 6

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related