How to Declare, Create and Initialize an Object in Java

A class is a blueprint for Object, you can create an object from a class. Let's take Student class and try to create a Java object for it.

How to Declare, Create and Initialize an Object in Java

Let's create a simple Student class which has name and college fields. Let's write a program to declare, create and initialize a Student object in Java.
package net.javaguides.corejava.oops;

public class Student {
    private String name;
    private String college;

    public Student(String name, String college) {
        super();
        this.name = name;
        this.college = college;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
    public String getCollege() {
        return college;
    }

    public void setCollege(String college) {
        this.college = college;
    }

    public static void main(String[] args) {

        Student student = new Student("Ramesh", "BVB");
        Student student2 = new Student("Prakash", "GEC");
        Student student3 = new Student("Pramod", "IIT");
    }
}
From the above program, the Student objects are:
Student student = new Student("Ramesh", "BVB");
Student student2 = new Student("Prakash", "GEC");
Student student3 = new Student("Pramod", "IIT");
Each of these statements has three parts (discussed in detail below):
Declaration: The code Student student; declarations that associate a variable name with an object type. 
Instantiation: The new keyword is a Java operator that creates the object.
Initialization: The new operator is followed by a call to a constructor, which initializes the new object.

Declaring a Variable to Refer to an Object

General syntax:
type name;
This notifies the compiler that you will use a name to refer to data whose type is a type. With a primitive variable, this declaration also reserves the proper amount of memory for the variable.
From the above program, we can declare variables to refer to an object as:
Student student;
Student student2;
Student student3;

Instantiating a Class

The new operator instantiates a class by allocating memory for a new object and returning a reference to that memory. The new operator also invokes the object constructor.
For example:
Student student = new Student("Ramesh", "BVB");
Student student2 = new Student("Prakash", "GEC");
Student student3 = new Student("Pramod", "IIT");
Note that we have used a new keyword to create Student objects.

Initializing an Object

The new keyword is followed by a call to a constructor, which initializes the new object. For example:
Student student = new Student("Ramesh", "BVB");
Student student2 = new Student("Prakash", "GEC");
Student student3 = new Student("Pramod", "IIT");
From the above code will call below constructor in Student class.
public class Student {
    private String name;
    private String college;

    public Student(String name, String college) {
         super();
         this.name = name;
         this.college = college;
    }
}

Reference


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