Access modifier

✅ What does access modifier do?

Allow access or hide class, field, constructor, method from outside class/package

• Developer should not change speaker volume outside speaker class

• 👎🏻 Before(without access modifier)

public class Speaker1 {
     int volume;
}

public class SpeakerMain1 {

    public static void main(String[] args) {
        speaker.volume = 200; //👎🏻 Can change speaker volume in main class
    }

• 👍🏻 After
• add private
• main class cannot access speaker.volume

public class Speaker2 {
    private int volume; //🟢 add private access modifier
}

public class SpeakerMain2 {

    public static void main(String[] args) {
        speaker.volume = 200; //🔴 compile error
        //👍🏻 cannot access speaker.volume
    }

✅ Access modifier

• private: same class
• default: same package(package private)
• protected: same package + inherit
• public: allow all access

✅ Where is access modifier used?

• field
• method
• contructor
• class

✅ Class and access modifier

• class can only be public or default

✅ Encapsulation

• make a class’s field and method together into a capsule
• 🟰 OOP
• Access modifier helps encapsulation safe

• by limiting access to field and method inside capsule

• ✔️ field should be private

• private field: field should not be altered from outside class

  • field should be accessed through method
  • 계좌에서 입금, 출금을 하기 위해 버튼을 누르지 우리가 직접 잔액을 바꿀수는 없음!
  • 입금, 출금은 버튼을 통해서 ➡️ field 접근은 method를 통해서
• ✔️ make the most method private
  • hide methods that should not be altered from outside class
  • limit access to method from outside
  • 꼭 필요한 method만 노출하기
  • 사용자는 입금, 출금만 간단하게 하고, 금액이 유효한지/잔액이 충분한지 등 로직은 숨김

✅ what is a good Encapsulation?

• field and method in one class(capsule)
• field are private
• field should be accessed through method
• only required method should be accessible from outside
• limited access to method as well

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