Learning Java OOP: Getting to know a constructor & destructor in Java

What is a Constructor?

A constructor is a special method that will be executed during an instance .

Usually this method is used to initialize or prepare data for objects.

Example of a constructor and how to make it

The following is a sample constructor:

The way to make a constructor is to write the name of the constructor method the same as the class name.

In the example above the constructor is written like this:

public User() {
    System.out.println("eksekusi method constructor...");
}

Make sure to provide a modifier publicto the constructor, because he will be executed when the object creation (instance) .

Let's try to create a new object from the class User:

User petani = new User();

So now we have a complete code like this:

The result when executed:

Parameter Constructor

A constructor is usually used to initialize data for classes.

To do this, we must make parameters as input for the constructor.

Example:

public class User {
    public String username;
    public String password;

    public User(String username, String password){
        this.username = username;
        this.password = password;
    }
}

In the class code Userabove, we add parameters username and passwordinto the constructor.

Then later when we create an object, we must add a parameter value like this:

User petani = new User("petanikode", "kopi");

Sample complete code:

package konstruktor;

public class User {
    public String username;
    public String password;
    
    public User(String username, String password){
        this.username = username;
        this.password = password;
    }
       
}


class DemoConstructor{
    public static void main(String[] args) {
        User petani = new User("petanikode", "kopi");
        System.out.println("Username: " + petani.username);
        System.out.println("Password: " + petani.password);
    }
}

The output results:

Destructor in Java

Destructor is a special method that will be executed when the object is deleted from memory.

Java itself does not have a destructor method, because Java uses a gerbage collector for memory management.

So the gerbage collector will automatically delete unused objects.

As for other programming languages, like C ++ we can make destructors themselves like this:

class User {  
public:  
   User( String *username );  // <-- ini constructor  
   ~User(); //  <-- ini destructor.  
private:  
   String username;  
   String password;  
}; 

Sumber: https://www.petanikode.com/java-oop-constructor