Understand java constructor

Introduction

From simple things, I will output java steadily. I am studying with the goal of passing java silver.

What is a constructor?

A method that is always executed when instantiated Used for variable initialization, etc.

How to write

Qualifier constructor name(){
Processing content
}

The constellator name will be the same as the class name.

I will write

`Main.java`


class Cat {
	String name;
	int age;
	
	//constructor
	Cat() {
		System.out.println("It will be executed when new is done ~");
	}
}

public class Main {
	public static void main(String[] args) {
		Cat obj = new Cat();
	}
}

Execution result

It will be executed when new is done ~

The constructor is running correctly when new.

You can also pass arguments.

`Main.java`


class Cat {
	String name;
	int age;
	
	//constructor
	Cat(String msg) {
		System.out.println("It will be executed when new is done ~" + msg);
	}
}

public class Main {
	public static void main(String[] args) {
		Cat obj = new Cat("I'm rumbling ~");
	}
}

Execution result

It will be executed when it is new ~

in conclusion

If you do not define a constructor, the default constructor will be defined at compile time. It has no arguments and the implementation is empty.

class Cat {
  Cat(){
  }
}

References

This article was written with reference to the following information.

-Oracle Certification Textbook Java Programmer Silver SE11