Why is there a packaging type?

Let the basic data type also have the characteristics of the object

private IntegerCache() {}

}

public class Main {

public static void main(String[] args) {

Double i1 = 100.0;

Double i2 = 100.0;

Double i3 = 200.0;

Double i4 = 200.0;

System.out.println(i1==i2);

System.out.println(i3==i4);

}

}

false

false

Get the latest interview manual In order to make basic types have the characteristics of objects , There are packaging types （ If we are using a collection type Collection You must make

Use the packaging type instead of the basic type ） Because the containers are filled object Of , This is where these basic types of wrapper classes are needed .

Automatic boxing ： new Integer(6); , Bottom call : Integer.valueOf(6)

Automatic dismantling : int i = new Integer(6); , Bottom call i.intValue(); Method realization .

The answer is found in the code below ：

The difference between the two ：

1. Different ways of declaration ： Base types are not used new keyword , The packaging type needs to be used new Keywords come in Empty allocated storage in heap

between ;

2. Storage mode and location are different ： The basic type is to store the values of variables directly on the stack , The wrapper type is to put the object in the heap , then

Use... By reference ;

3. Different initial values ： The initial value of the basic type is as follows int by 0,boolean by false, The initial value of the wrapper type is null;

4. Use in different ways ： Base types are simply assigned and used directly , While the wrapper type is in the collection such as Collection、Map Will use

To .