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

Understanding constructors 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:
Example constructor in Java
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:
Example constructor in Java
The result when executed:
Sample output constructor

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:
Sample output constructor with parameters

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
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