CODEWITHSUNDEEP
java
Rajendra_Prasad
Rajendra_Prasad

Reputation: 1304

how to store recent values in a variable in java programming?

In my java program,I need to store the recent values in a variable and my code is as shown below 

public class Exmp2 
{

        int noOfInstances;
    public Exmp2() 
    {
        noOfInstances++;
    }
    public static void main(String[] args){
        Exmp2 e1=new Exmp2();
        System.out.println("No. of instances for sv1 : " + e1.noOfInstances);

        Exmp2 e2=new Exmp2();
        System.out.println("No. of instances for sv1 : "  + e2.noOfInstances);
        System.out.println("No. of instances for st2 : "  + e2.noOfInstances);

        Exmp2 e3=new Exmp2();
        System.out.println("No. of instances for sv1 : "  + e3.noOfInstances);
        System.out.println("No. of instances for sv2 : "  + e3.noOfInstances);
        System.out.println("No. of instances for sv3 : "  + e3.noOfInstances);
    }
}

My output should be 1 2 2 3 3 3 but am getting 1 1 1 1 1 1 can you give solution?

Upvotes: 5

Views: 13362

Answers (9)

user2243268
user2243268

Reputation:

You have to declare you variable as static : static variable always stores the recent values,its static variable would store in static pool

static int noOfInstances;

Upvotes: 2

Joe2013
Joe2013

Reputation: 997

See the below example on how to use the static variable for instance count

package com.stackoverflow.test;

public class Exmp2 {

    static int noOfInstances;

    public Exmp2() {
        noOfInstances++;
    }

    public static void main(String[] args) {
        System.out.println("No. of instances at this point "
                + Exmp2.noOfInstances);
        Exmp2 e1 = new Exmp2();
        System.out.println("No. of instances at this point "
                + Exmp2.noOfInstances);
        Exmp2 e2 = new Exmp2();
        System.out.println("No. of instances at this point "
                + Exmp2.noOfInstances);
        Exmp2 e3 = new Exmp2();
        System.out.println("No. of instances at this point "
                + Exmp2.noOfInstances);
    }
}

Upvotes: 1

aizaz
aizaz

Reputation: 3062

You Should declare your variable int noOfInstances; as static, in your code the instances are taking default value 0.

Upvotes: 2

AmitG
AmitG

Reputation: 10543

Make noOfInstances static like given below,

static int noOfInstances; // static are shared among all objects created.

and no need to call e1.noOfInstances instead you can call Exmp2.noOfInstances

Instance (non-static) variable are copied in Objects whereas static variables are not copied in object. static are at the class level. Every object can see it.

Upvotes: 2

Rahul
Rahul

Reputation: 45070

Declare your noOfInstances variable as static.

static int noOfInstances;

Since its not static, for every new Exmp2() a noOfInstances is created for that instance, with the default value as 0.

Upvotes: 7

G.S
G.S

Reputation: 10871

Whenever you do new Exmp2(); then noOfInstances assigned to 0 as you are instantiating a new Object, Make noOfInstances as static so that its scope shifts to class level.

Upvotes: 1

Narendra Pathai
Narendra Pathai

Reputation: 41955

The variable should be declared static.

Why? Because presently your variable noOfInstances is not static and for each instance of your class you create noOfInstances variable will also be created and always the value will be 1. So on declaring it static it is shared between all the instances of this class and will have the correct value.

Static variables are created when the class is loaded and are shared across all the instances.

Upvotes: 2

Joey Roosing
Joey Roosing

Reputation: 2155

noOfInstances should be declared static. For example:

static int noOfInstances;

This might be an interesting read. It should have an example with a similar situation as yours:

static keyword

In short, static literally makes a variable shared among instances of a given class. If you have a variable that is not static every instance will have its own private value for that variable. While a statically declared variable will have the same value in all instances of a class.

Upvotes: 2

gefei
gefei

Reputation: 19786

you havew to declare noOfInstances to be static

    static int noOfInstances;

otherwise every new instance create by new will have its own value of noOfInstances, beginning at 0 again

Upvotes: 3

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