Mutable 🆚 Immutable, Final

✅ Mutable

can be modified after initialization
encapsulate: getter, setter, private, final field
need to synchronize access for multi thread

• String Builder
• Stirng Buffer
• java.util.Date

✅ Immutable

cannot be modified after initialization
힙 영역에 저장된 값을 변경할 수 없는 것
preferred in multi threading, as it guarantees thread saftey
공유 자원이 Immutable하다면 여러개의 쓰레드가 읽고 써도 안 바뀌니까 safe!

• int
• long
• float
• double
• String
• legacy, wrapper classes

I changed value from 1 to 3. Does this mean Integer is mutable?

Integer i=1;
i=3;
//바꿨는데요??
// 아님, 힙 영역에 새로운 객체가 생성된 것이다.

NO. New object in heap created. and Integer with value 1 will be discared by GC

✅ Final

초기화 이후에 값 변경 불가
immutable

final Integer i=1;
i=3; //❌ compile error.

https://www.geeksforgeeks.org/mutable-and-immutable-objects-in-java-1/