# Java basic knowledge

#### Primitive type and Autoboxing/Unboxing
Eg: int vs Integer
int is primitive type, while Integer is a class (eg: Integer.parseInt("1") is a call of Integer's class method)
All primitive type in Java has an equivalent wrapper class:
* byte -> Byte
* short -> Short
* int -> Integer
* long -> Long
* boolean -> Boolean
* char -> Character
* float -> Float
* double -> Double

Wrapper class inherit from Object class and primitive don't.
##### Java 5 have autoboxing.
Autoboxing is the automatic conversion that the Java compiler makes between the primitive types and their corresponding object
wrapper classes.

Auto boxing example
```java
List<Integer> li = new ArrayList<>();
int i = 2;
li.add(i);
```
This is actually
```java
li.add(Integer.valueOf(i));
```
Unboxing example
```java
int m = li.get(0);
```
This is actually
```java
int m = li.get(0).intValue();
```