> For the complete documentation index, see [llms.txt](https://heunnajo.gitbook.io/java/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://heunnajo.gitbook.io/java/java.lang-package-and-useful-class/auto-boxing-and-auto-unboxing-1.md).

# Auto-boxing and (auto)Unboxing

Auto-boxing : primitive type=>object\
Unboxing : object=>primitive type

```java
ArrayList<Integer> list = new ArrayList<Integer>();
//only object is possible but compiler does automatically
list.add(10);//list.add(new Integer(10));

int value = list.get(0);//list.get(0).intValue()
```

intValue(), valueOf() : Integer -> int

```java
int i = 10;

//기본형을 참조형으로 형변환(형변환 생략가능)
Integer intg = (Integer)i;//Integer intg = Integer.valueOf(i);
Object obj = (Object)i;//Object obj = (Object)Integer.valueOf(i);

//참조형 변수
Long lng = 100L;//Long lng = new Long(100L);

//참조형과 기본형간의 연산 가능
int i2 = intg + 10;
//참조형간의 덧셈도 가능
long l = intg + lng;

Integer intg2 = new Integer(20);
int i3 = (int)intg2;//참조형을 기본형으로 형변환도 가능(형변환 생략가능)


```

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