Java Tutorial : What is an Object[Student]?

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What is an Object in Java? Student Class and Objects Explained

In Java Object-Oriented Programming (OOP), a class acts as the blueprint or template, while an object is a concrete instance created from that blueprint. To truly understand how objects work in memory and in code, let us look at a real-world example: modeling a Student.

1. Defining States and Behaviors in Student Class

Every student entity possesses characteristics (states) and actions they can perform (behaviors):

• States (Attributes / Variables): name, age, color, and sex.
• Behaviors (Actions / Methods): eating(), drinking(), and running().

2. Creating Multiple Objects from One Blueprint

Using a single Student blueprint, we can create multiple distinct student instances with unique state values:

• Student 1 (Peter): Age 3, white, male, eats more food, drinks more water, runs fast.
• Student 2 (John): Age 4, brown, male, eats less food, drinks more water, runs slow.
• Student 3 (Julia): Age 2, white, female, eats less food, drinks less water, runs fast.

3. Syntax for Object Creation in Java

In Java, an object is instantiated using the new keyword followed by the constructor:

ClassName objectName = new ClassName();

Here, the left side (ClassName objectName) represents the reference type, and the right side (new ClassName()) represents the actual object type allocated in memory.

4. Code Example: Student and StudentDemo

Student.java

public class Student {
    // States / Attributes
    String name;
    int age;
    String color;
    String sex;

    // Behaviors / Methods
    public void eating() {
        System.out.println(name + " is eating.");
    }

    public void drinking() {
        System.out.println(name + " is drinking water.");
    }

    public void running() {
        System.out.println(name + " is running.");
    }
}

StudentDemo.java

public class StudentDemo {
    public static void main(String[] args) {
        // Creating student object for Peter
        Student peter = new Student();
        peter.name = "Peter";
        peter.age = 3;
        peter.color = "White";
        peter.sex = "Male";

        displayStudentInfo(peter);
        peter.eating();
        peter.drinking();
        peter.running();
    }

    public static void displayStudentInfo(Student student) {
        System.out.println("Name: " + student.name);
        System.out.println("Age: " + student.age);
        System.out.println("Color: " + student.color);
        System.out.println("Sex: " + student.sex);
    }
}

5. Key Takeaways

• A class defines what properties and methods every object of that type will have.
• Each object maintains its own separate copy of instance variables.
• Methods execute actions based on the object's specific internal state.

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Watch More Java Tutorials from Ram N Java

• Java Object Class Explained | Java Tutorial
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Java Tutorial : What is an Object[Student]?

Java Tutorial : What is an Object[Student]?

Student.java

/**
 * Student class is the blueprint from which individual student objects can be
 * created.
 */
public class Student
{
    String name;
    int age;
    String color;
    String sex;

    public void eating(String string)
    {
        System.out.println(name + " " + string);
    }

    public void drinking(String string)
    {
        System.out.println(name + " " + string);
    }

    public void running(String string)
    {
        System.out.println(name + " " + string);
    }
}

StudentDemo.java

public class StudentDemo
{
    public static void main(String[] args)
    {
        Student peter = new Student();

        /*
         * Setting States/Attributes/Properties/Characteristics.
         */
        peter.name = "Peter";
        peter.age = 3;
        peter.color = "white";
        peter.sex = "male";

        displayStudentInformation(peter);
        
        System.out.println("\nBehaviors");
        System.out.println("----------");
        
        peter.eating("can eat more foods");
        peter.drinking("can drink more water");
        peter.running("can run fast");
        
        System.out.println("*********************************************");
        
        Student john = new Student();

        /*
         * Setting States/Attributes/Properties/Characteristics.
         */
        john.name = "John";
        john.age = 4;
        john.color = "brown";
        john.sex = "male";

        displayStudentInformation(john);
        
        System.out.println("\nBehaviors");
        System.out.println("----------");
        
        john.eating("can eat less foods");
        john.drinking("can drink more water");
        john.running("can run slow");
        
        System.out.println("*********************************************");
        
        Student julia = new Student();

        /*
         * Setting States/Attributes/Properties/Characteristics.
         */
        julia.name = "Julia";
        julia.age = 2;
        julia.color = "white";
        julia.sex = "female";

        displayStudentInformation(julia);
        
        System.out.println("\nBehaviors");
        System.out.println("----------");
        
        julia.eating("can eat less foods");
        julia.drinking("can drink less water");
        julia.running("can run fast");
        
        System.out.println("*********************************************");
    }

    private static void displayStudentInformation(Student student)
    {
        System.out.println("Attributes");
        System.out.println("--------------");

        System.out.println("Name : " + student.name);
        System.out.println("Age : " + student.age);
        System.out.println("Color : " + student.color);
        System.out.println("sex : " + student.sex);
    }
}

Output

Attributes
--------------
Name : Peter
Age : 3
Color : white
sex : male

Behaviors
----------
Peter can eat more foods
Peter can drink more water
Peter can run fast
*********************************************
Attributes
--------------
Name : John
Age : 4
Color : brown
sex : male

Behaviors
----------
John can eat less foods
John can drink more water
John can run slow
*********************************************
Attributes
--------------
Name : Julia
Age : 2
Color : white
sex : female

Behaviors
----------
Julia can eat less foods
Julia can drink less water
Julia can run fast
*********************************************

To Download StudentDemoObjectApp Project Click the below link:
https://sites.google.com/site/javaee4321/java/StudentDemoObjectApp.zip?attredirects=0&d=1

See also:

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