There are basic types in JAVA Why do you have a wrapper type? __java

The basic data types and packing types in Java are:

Basic Type	Wrapper Type
Boolean	Boolean
Char	Character
Int	Integer
Byte	Byte
Short	Short
Long	Long
Float	Float
Double	Double

Why are there two types of these?

We all know that in the Java language, new objects are stored in the heap, we use them through references in the stack, but for a series of types such as int that are often used, it's not very efficient to store them in a heap with new-especially simple small variables. So there's the basic type, like C + +, where Java uses a similar approach, which is more efficient when it is not created with the new keyword, but directly by storing the value of the variable in the stack.

Why do you have a packing type when you have a basic type?

We know that Java is a programming language of object-oriented objects, the basic type does not have the nature of the object, and in order for the base type to also have the object's characteristics, the wrapper type appears (such as we must use the wrapper type instead of the base type when using the collection type collection), which is equivalent to the base type " Wrapping up, makes it have the nature of the object, and adds attributes and methods to it, enriching the basic type of operation.

In addition, when you need to put something in the Arraylist,hashmap, the basic type like int,double is not put in, because the container is loaded object, this is the need for these basic types of wrapper class.

The two convert to each other:

1, int turn integer

int i = 0; Integer II = new Integer (i);
2, integer turn int

Integer II = new integer (0); int i = Ii.intvalue ();

the difference between the two:

1. Different ways of declaring:

The base type does not use the New keyword, and the wrapper type needs to use the New keyword to allocate storage space in the heap;

2. Different storage mode and location:

The basic type is to store the value of the variable directly on the stack, and the wrapper type is to place the object in the heap and then use it by reference;

3. Different initial values:

The initial value of the base type, such as int is 0,boolean to false, and the wrapper type's initial value is null;

4. Different ways of use:

Basic types are directly assigned directly to use, and package types are used when collections such as collection, map.