[Beginner] Java class field method / encapsulation (getter setter) [Note 25]

Class field / class method

Class field

There was an instance field, but a class field that belongs to a class There is also that. As a concrete example, count how many instances were created There is something called count. [Example]

class Person{
 public static int count = 0;
 //...Abbreviation

Person(String firstName,...);{
 Person.count++;
... //↑ By doing this, each time an instance is created, it will be added by 1.

Class method

class Person{
 public static int count = 0;
 //...Abbreviation
 public static void printCount(){
  System.out.println("total" + Person.count + "Is a person");
 }
}

Class methods can be called even if no instance is created.

//<Main.java>At
class Main{
 public static void main(String[]args){
  Person.printCount();
  Person person1 = new Person( //...Abbreviation);
  Person.printCount();
 }
}

output: 0 people in total 1 person in total

Note that both class fields and class methods have "static"!

Rewriting fullName with null

The content of the fullName created in the previous article was "firstName + lastName" I will write a concrete example of how to write when you want to add middleName ↓ (Since some instances do not have a middleName, they are indicated by conditional branching.)

If nothing is done, "null" is usually entered in the middleName (String type) part. (0 for int / 0.0 for double / false for boolean)

class Person{
...
 public String fullName(){
  if (this.middleName == null){
   return this.firstName + " " + this.lastName;
  }else{
   return this.firstname + " " + this.middleName + " " + this.lastName;
  }
}
...

Encapsulation

A mechanism used to prevent a defined object from being destroyed by touching it. An image like the inside of a personal computer. Until now, it was written as "public", but now it is written as "private".

Private fields cannot be accessed from the Main class, such as changes.

Getter

To make it private and then safely get the value from outside the class A mechanism that returns the value of a field. Write "get field name".

Setter

A mechanism used when you want to change the value outside the class after setting it to private. Write "set field name".

//<Person.java>At...After writing the constructor ↓
...
 public String getMiddleName() {
  return this.middleName;
 }
//First, define the getter, then define the setter
 public void setMiddleName(String middleName) {
  this.middleName=middleName;
 }
...

//<Main.java>At...Person person1 = new Person("Yamada","Hanako"...);If it is written.
...
person1.setMiddleName("Claire"); //If you want to change it.

System.out.println("Middle name" + person1.getMiddleName() + "Changed to");

Let's start the review task

・ When defining a getter

public String getName(){
 return this.name;

In the above case, I forget (), so review it carefully. Remember again.

from now on

To advance so that you can write the object orientation so far by yourself I will review how to write while using Progate and other sites. If you have any questions or findings, I will write them again.