Object in Java - What is Object, State & Behaviour

Object in Java - State and Behaviour Explained

Table of Contents

• What is Object?
• i. State
• ii. Behaviour
• Object Example with Code
• Output

Object

1. Object is a real-world entity.
2. Object contains two things:
   i. State
   ii. Behaviour

i. State

• State can change.
• State is also called attributes or variables.
• State is used to represent type of data or state of an Object.

For Example:

• Student is an Object where roll is a state and roll type is int.
• Student is an Object where name is a state and name type is String.
• Student is an Object where marks is a state and marks type is float.

ii. Behaviour

• Behaviour of an Object never changes (method definition remains same).
• Behaviour is represented as a method.

For Example:

• Student is an Object where study() or learn() is a behaviour.
• Pen is an Object where write() is a behaviour.
• AC is an Object where on(), off(), swing() etc. are behaviours.

Object Example - Practical Code

// This is a template or blueprint of an Object.
// This class contains information about Student.
// But you don't know the state of student, that's why this type of class is called Template or Blueprint.
class Student {
    String name;
    int roll;
}

// This class is used for testing.
class Test {
    // This is an entry point from where your program starts.
    public static void main(String[] args) {
        // This is an object or instance
        // This object initializes the state with default values.
        // new is an operator/keyword used to create blank/new memory.
        // Student() is a constructor which initializes the values.
        // After completion it returns same type of address where data is allocated.
        // std works as a reference variable who points to address of default values.
        Student std = new Student();

        // If you want to change default values to actual values:
        std.name = "suresh singh";
        std.roll = 123;

        // To access data from that location:
        System.out.println(std.name);
        System.out.println(std.roll);
    }
}

Output is:

suresh singh
123

Conclusion

Object is an instance of class that has state (variables) and behaviour (methods). Class is blueprint, object is real entity created using new keyword. Understanding state and behaviour is foundation of OOP.

Next: Class vs Object, Constructor in Java, new keyword