Non-Access modifiers (기타 제어자)

Provide additional meaning, such as static behavior, finality, synchronization, etc.

• they are loaded into memory when the class is first loaded (usually when it’s first accessed or used), and they stay loaded until the class is unloaded — typically at program termination
• can use multiple of them at the same time

Modifier	Applies To	Meaning (설명)
static	Fields, methods, blocks, inner classes	Belongs to the class instead of instances
final	Variables, methods, classes	Cannot be changed/overridden/inherited
abstract	Classes, methods - Abstraction - Classes & Interfaces	Class cannot be instantiated; method has no implementation and must be overridden by subclasses
(there are more)

Static Members

• static variables
• static methods
• Static blocks
• Static classes (only inner)
• Static import
• Singleton Patterns

Static vs instance members

구분	static 멤버	인스턴스 멤버
메모리 영역	클래스 영역	힙 영역
접근 방식	클래스명.멤버	객체.멤버
공유 여부	모든 인스턴스 간 공유	객체마다 별도 보유
생성 시점	클래스 로드 시	new 생성 시
사용 예시	공통 속성, 유틸리티 메서드	객체의 개별 상태 관리

Static Members Initialization Order

• Instance Initialization Block
  • a block of code inside a class but outside any method or constructor, written simply as { ... }
  • runs every time an object (instance) of the class is created, before the constructor is executed

Static member initialization order:

순서	단계	설명 (Korean)	Description (English)
1	JVM 기본값	static 변수에 자료형에 맞는 기본값이 할당됨	JVM gives default values to static fields (e.g. 0, null, false)
2	명시적 초기화	static 변수에 대입한 초기값 실행	Static fields with assigned values get initialized
3	static 초기화 블록	static {} 안의 코드 실행	static {} block runs for more complex logic

class Example {
    static int a;              // 기본값 0
    static int b = 10;         // 명시적 초기화
    static {
        a = 100;               // static 초기화 블록
    }
}