Java class definition and instantiation

Class definition and instance generation

Use "new class name ()" to instantiate a class. [Example]

class Main {
  public static void main(String[] args) {
  new Person();  //Person(This time people)Create an instance of the class
  }
}

`Person.java`


class Person{
}

Instance to variable

To assign an instance to a variable, use "class type variable name = new class name ()". When assigning an instance, specify the class type, and the class name becomes the class type as it is. [Example]

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

`Person.java`


class Person{
}

Instance method

The instance method uses "public return type method name ()".

`Main.java`


class Main {
  public static void main(String[] args) {
    Person person = new Person();  //void is the return type
    person.hello();
  }
}

`Person.java`


class Person {
  public void hello() {
  System.out.println("Good morning");
  }
}

Instance field definition

For the instance field definition, add public before the variable definition, such as "public data type variable name". [Example]

`Person.java`


class Person {
  public String name;
}

String name defines the definition to put the name. For the instance field, use "instance name.field name". [Example]

`Main.java`


~abridgement~
    Person person = new Person();
    person.name("Sato");
    System.out.println(person.name);  //person.Getting the value of name with name
~abridgement~

[Example]

`Main.java`


class Main {
  public static void main(String[] args) {
    Person person = new Person();
    person.hello();
    person.name = "Sato";
    System.out.println(person.name); 
    }
}

`Person.java`


class Person {
  public String name;
  public void hello() {
    System.out.println("Good morning");
  }
}

this Use the "this" variable to access the instance field in the method. this can only be used in method definitions within a class. This is replaced with the instance calling the method when it is called. [Example]

`Main.java`


class Main {
  public static void main(String[] args) {
    Person person = new Person();
    person.hello();  //person calls this
    person.name = "Sato";
    System.out.println(person.name); 
    }
}

`Person.java`


class Person {
  public String name;
  public void hello() {
    System.out.println("Good morning" + this.name);  //this.(This time)name field of hello method
  }
}