Constructor in Java

Constructor in Java. In this Article we will look into our class and learn how to create a constructor.

What is a Constructor

No	Constructor Features
1	A contructor is created automatically , when you did not create or declare a constructor specifically in your class.
2	Structure of the Constructor is similar to method , it will be called automatically when the class is created.
3	A Constructor can be Private or Public. If Public , the constructor will be able to be access by other constructor.
4	Constructor enable you to set a default or initial value in your Class. If a New Object is created it will overwrite the Constructor Default value.
5	Constructor can throw exception when un recoverable events happens .
6	You can create more than one Constructor in a class .
7	You can create more than one Constructor in a class .

 Constructor vs Method ( Constructor in Java)

No	Attributes	Constructor	Method
1	Called Automatically when a new Object is created	Yes	No
2	Considered as Member of a Class	No	Yes
3	Name of the Constructor must be same as the Class	Yes	No
4	Return Type	No	Yes
5	Created automatically in the System	Yes	No

Lets Step into the Code and learn how to create a constructor in a class

In the example below , i will create 2 Class . The First Class i name it the “Dog” Class while the second class i name it “AccessDog”  Class.The Dog class allows you to create a new object or instance for dogs.The AccessDog  class function is to access the Dog Class.

Dog Class

1. First , i created a Class name “Dog”
2. 4 Private Variable which can only be accessible within this Class is Declare (dogname, dogbreed, dogcolor, dogAge)
3. I set my first Constructor with the name “Dog ” as explain above the Constructor Name my be same and identical to the Class
4. The first Constructor does not pass through any parameter through its parentheses
5. I have set some default value inside my First Constructor
6. I Set my second Constructor which allow User to Pass through Parameter through its Paratheses
7. this.dogname= dogname;means, to assign the value in public Dog(String dogname ,String dogbreed, String dogcolor ,int dogAge)
   into private String dogname;
8. The Remaining code below shows how to code the setter and the getter for the class. Refer here on how to code the Setter and Getter.

 

package oop2;

public class Dog {
	
	private String dogname;
	private String dogbreed;
	private String dogcolor;
	private int dogAge;
	
	public Dog(){
		this.dogname = "wangwang";
		this.dogbreed = "labrador";
		this.dogcolor = "brown";
		this.dogAge = 2;
			
		
	}
	
	public Dog(String dogname ,String dogbreed, String dogcolor ,int dogAge){
		this.dogname= dogname;
		this.dogbreed=dogbreed;
		this.dogcolor=dogcolor;
		this.dogAge=dogAge;
		
		
	}
	
	
	public String getDogname() {
		return dogname;
	}

	public void setDogname(String dogname) {
		this.dogname = dogname;
	}

	public void setDogBreed(String dogbreed){
		
		this.dogbreed = dogbreed;
		
	}
	
	public String getDogBreed(){
		
		return this.dogbreed;
		
	}

	public String getDogcolor() {
		return dogcolor;
	}

	public void setDogcolor(String dogcolor) {
		this.dogcolor = dogcolor;
	}

	public int getDogAge() {
		return dogAge;
	}

	public void setDogAge(int dogAge) {
		this.dogAge = dogAge;
	}
	
		  	
	
}

 

AccessDog Class

1. Now we have finished our Dog class lets create our AcessDog Class
2. To use the Scan Function i will need to import java.util.*;
3. Declare 4 Static Variable to be Use later below in the program
4. Declare 4 new Scanner Object call inputScan1, 2,3,4
5. Create a new Dog name called origin using the Default Constructor
6. called the Getter method of the dog class to print out the Default Value
7. Print out the Statement to request the user to input the Dog name
8. inputDogname = inputScan1.nextLine(); Assign the value the user key in the Scanner object named inputScanner1 into the inputDogname variable
9. Same apply to the remaining below
10. Dog inputDog =new Dog(inputDogname,inputBreed,inputColor,inputAge); Assign the User input into the second constructor that we created
11. System.out.println(inputDog.getDogname()); Access the Dog Class Getter and print out all the Dog attributes that the User have enter just now
12. Close all the Scanner Objects.

package oop2;
 import java.util.*;


public class AccessDog {
	
	static String inputDogname;
	static String inputBreed;
	static String inputColor;
	static int  inputAge;


	public static void main(String[] args) {
		
		Scanner inputScan1 = new Scanner(System.in);
		Scanner inputScan2 = new Scanner(System.in);
		Scanner inputScan3 = new Scanner(System.in);
		Scanner inputScan4 = new Scanner(System.in);
		
		Dog origin =new Dog();
		
		//Print the Default Dog name
		
		System.out.println(origin.getDogname());
		System.out.println(origin.getDogBreed());
		System.out.println(origin.getDogcolor());
		System.out.print(origin.getDogAge());
		                   	
		
		System.out.println("Input Your Dog Name ?");
		inputDogname = inputScan1.nextLine();
		System.out.println("Input Your Dog Breed ?");
		inputBreed = inputScan2.nextLine();
		System.out.println("Input Your Dog Color ?");
		inputColor= inputScan3.nextLine();
		System.out.println("Input Your Dog Age ?");
		inputAge =inputScan4.nextInt();
		
		//Input all value into the Constructor
		Dog inputDog =new Dog(inputDogname,inputBreed,inputColor,inputAge);
		
		System.out.println(inputDog.getDogname());
		System.out.println(inputDog.getDogBreed());
		System.out.println(inputDog.getDogcolor());
		System.out.print(inputDog.getDogAge());
		
		
		inputScan1.close();
		inputScan2.close();
		inputScan3.close();
		inputScan4.close();

	}

}

Results as shown below

Well this Wrap up the article about Constructor in Java.

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