Reference Variable in Java

What is a reference variable in java?

• Reference variable in java is a class type variable.
• In other words, declaring a variable along with class name is nothing but a reference variable.
• Reference variable stores the address of an object which acts as a way to access an object
• By using reference variable we can access non static members of the class.
• If no object is passed into the reference variable then by default null value will be stored .

Example

class Demo {
    int a=20;
    void test(){
        System.out.println("Test Method");
    }
}
class MainApp{
    public static void main(String[] args) {
        //Creating object for class Demo
        Demo d1=new Demo();
        //printing reference variable
        System.out.println(d1);
        //Accessing non-static members of Demo class using reference variable
        System.out.println("A value is "+d1.a);
        d1.test();
    }
}

Output:

ReferenceVariable.Demo@1b28cdfa
A value is 20
Test Method

To understand the above example let us have a look at the following points:

• When we create an object for the class Demo, the address of object new Demo() gets stored into the reference variable d1.
• When we print the reference variable the output contains fully qualified name of the class along with the hexadecimal value(hash code). In this case, it is ReferenceVariable.Demo@1b28cdfa.
• In the next step, we have accessed variable ‘a’ and method test() from demo class by using reference variable d1.

Is it possible to create an object with multiple references?

• It is possible to create a single object with multiple reference variables.
• It means we can copy address of one variable into another variable.
• If we create object with multiple references then all reference variables will be having same address.

Example:

class Sample {
    void display(){
        System.out.println("Display Method");
    }
}
class MainApp1{
    public static void main(String[] args) {
        Sample s1=new Sample();
        //Creating a copy of reference variable for the same object
        Sample s2=s1;
        //comparing the address for both reference variable
        System.out.println(s1==s2);
    }
}

Output:

true