How to Find Number of Objects Created in Java

In Java, when we create an object of the class, the constructor of the class is always called, by default. We can count the number of objects directly if we keep tracking how many times the constructor is called. In this section, we will learn how to count the number of objects.

In order to count the number of objects, we need to add a count variable in the constructor and increments its value by 1 for each invocation. Remember that the variable count must a class-level variable. Now, the problem is that class-level variables have different values for each object, then how the value will be updated? So, declare the variable (count) as static.

The reason to make the variable static is that the static variable has only a copy per class that is shared by all objects of the class. By declaring the variable as static, all objects update the value of the variable.

Let's implement the logic in a Java program.

CountObject.java

public class CountObject
{
//variable to keep track of objects
private static int count;
//constructor of the class
public CountObject() 
{
// increase the count variable by 1
count++;
}
public static void main(String args[]) 
{
//creating objects
CountObject ob1 = new CountObject();
CountObject ob2 = new CountObject();
CountObject ob3 = new CountObject();
CountObject ob4 = new CountObject();
CountObject ob5 = new CountObject();
//prints number of objects
System.out.print("Total Number of Objects: " + CountObject.count);
}
}

Output:

Total Number of Objects: 5

The above program can also be written as follows:

ObjectCount.java

public class ObjectCount
{
static int count=0;
public static void main(String args[])
{
ObjectCount c1=new ObjectCount(); 
c1.count();
ObjectCount c2=new ObjectCount();
c2.count();
ObjectCount c3=new ObjectCount(); 
c3.count();
System.out.println("Total Number of Objects: "+count);
}
//function counts the number of objects
static void count()
{
count++;
}
}

Output:

Total Number of Objects: 3

Let's Create another Java program for the same.

EmployeeDemo.java

class Employee
{
public String name;
public int salary; 
public static int count=0;
//creating a constructor of the class
Employee(String name, int salary)
{
this.name= name;
this.salary= salary;
//increments the variable count by 1
count++;
}
}
public class EmployeeDemo
{
public static void main(String args[])
{
//creating objects    
Employee emp1 = new Employee("John", 20000);
Employee emp2 = new Employee("Tom", 60000);
Employee emp3 = new Employee("Andrew",29000);
Employee emp4 = new Employee("Mathew", 50000);
//prints total number of objects
System.out.println ("There are " + Employee.count + " objects in this class.");
}
}

Output: