CODEWITHSUNDEEP
javavariablescount
Neod
Neod

Reputation: 1

Confuse with Count usage in this code.

I have a problem knowing what a part of this code works.

Here it is: 

public class fia1 {
  public static void main(String [] args) {
   Band b0 = new Band();
   b0.name = "Beastie";
   b0.age = 25;
   Band b1 = new Band();
   b1.name = "Orchestra";
   b1.age = 100;
   System.out.println(b0.count);

   Band b2 = new Band();
   b2.name = "Polka";
   b2.age = 5;

   System.out.println("Names: " + b0.name + " " + b1.name + "
   " + b2.name);
   System.out.println(Band.count);
   b1 = b2;
   b1.age = 10;
   b0.age = b2.age + b0.age;

   System.out.println("Ages = " + b0.age + " " + b1.age + " "
   + b2.age);
    }
      }

  class Band {
   String name;
   int age;
   static int count = 1;
   Band() {
   count = count * 2;
   }
     }

So what this print is:

4
Names: Beastie, Orchestra, Polka
8
Ages: 35, 10, 10

I am confused as to how I get a 4 from my first count. Also I know that 

 static int count = 1;

is where I am misunderstanding. Is this how java counts the variables? by 1, then 2 is Beastie, 3 is Orchestra and 4 is Polka? I really don't know how this is working. Thanks for your help!

Upvotes: 0

Views: 88

Answers (3)

Walter Wu
Walter Wu

Reputation: 59

the count field in your Band class is a static field or class variable, meaning that all object of the Band class share it. Each time the constructor is called, count is updated. If you want to learn more about class variables, you can check out this Java documentation

Upvotes: 1

dat3450
dat3450

Reputation: 954

You are using a static variable in static int count = 1;, which means every time you create a new Band the variable will be doubled for all Bands (since count = count * 2;)

See code below with comments that explains what happens:

public static void main(String [] args)
{
    Band b0 = new Band(); //Count becomes 1*2 = 2.
    b0.name = "Beastie";
    b0.age = 25;

    Band b1 = new Band(); //Count becomes 2*2 = 4.
    b1.name = "Orchestra";
    b1.age = 100;
    System.out.println(b0.count); //Prints 4.

    Band b2 = new Band(); //Count becomes 4*2 = 8.
    b2.name = "Polka";
    b2.age = 5;

    System.out.println("Names: " + b0.name + " " + b1.name + " " + b2.name);
    System.out.println(Band.count); //Prints 8.
    b1 = b2;
    b1.age = 10;
    b0.age = b2.age + b0.age;

    System.out.println("Ages = " + b0.age + " " + b1.age + " " + b2.age);
}

Upvotes: 2

Drone6251
Drone6251

Reputation: 128

Since your variable count is static, as it's declared as a static int count = 1;, each new construction of the class will perform any actions on count to all objects that have count. Anotherwords, when you call b1, the count = count * 2; command affects all instances of count, so the count variable in b0 is also doubled as well.

Hence, when you first construct band() with b0, it takes count and sets it equal to 1 * 2 = 2. The second instance of band() with b1 causes all instances of count to be equal to itself * 2. So, the count in b1 is equal to 1*2 = 2, and the count in b0 is equal to 2*2 = 4.

Upvotes: 0

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