Basic data type and reference data type in Java

The future of garlic 2021-01-21 23:47:05
basic data type reference data


One 、 Basic data type

  • byte、short、int、long( Integer types )
  • float、double( Floating point type )
  • char( Character )
  • boolean( Boolean type )

Java Most of the data is stored in the stack .

  • The stack area : Store local variables , Object declaration reference, etc .

  • Heap area : Deposit new keyword Create a class ( Contains member variables ) And arrays .

Advantages and disadvantages of heap and stack

  • The advantages of stacks : Stack data can be share , Access speed is faster than heap fast .   The disadvantage is that : In stack The data size and life cycle are determined Of .

  • The advantages of heaps : Sure Dynamically allocate memory size , You don't have to tell the compiler the lifetime . The disadvantage is that : The access speed is faster slow .

Take a chestnut , Here's the picture :

  • The compiler creates a... In the stack a References to , Then look up the stack with the literal value of 5 References to , take a Point to 5 The address of , If not found , I'll open up an address

    Deposit the literal value 5, And then a Point to the address . Definition int c=5; Because there are literal values in the stack 5, all c Will point directly to 5 The address of . Make a=8, Because it's in the stack

    There is no literal value for 8 References to , All will open up an address to store 8,a It will point back to 8 The address of ,c The direction of is not affected by a influence ,c The value of .

Two 、 Reference data type

1. Class( class )

2. Interface( Interface )

3. Array( Array )

  • Java yes object-oriented Language , It makes corresponding wrapper classes for each basic data type ( See the previous table ), That is to say, it implements the basic type variable to Packaging

    Object conversion . The reference type is generally through new keyword To create ,( object ) It's in memory Pile up in , Available at run time Dynamic allocation of memory size . quote

    The address of the variable content is stored in the variable , It's in memory Stack in . When reference type variables are not used ,Java The internal garbage collector GC Will automatically recycle .

1. Code example -Class:

public class Demo {
String Name;
int Age;
double Score;
Demo(String Name,int Age,double Score){
// Define a constructor with three arguments , To initialize
this.Name=Name;
this.Age=Age;
this.Score=Score;
};
public static void main(String[] args) {
Demo d1=new Demo(" Xiao Wu ",20,98);
Demo d2=new Demo(" Small days ",19,80);
}
}

  • The reference itself is reserved in Stack Medium , The object referred to by reference is stored in Pile up Medium .

2. Code example -Interface

interface Animal {// Definition Animal Interface
public void eat();
public void speak();
}
public class Dog implements Animal {//Dog Class implementation Animal Interface
public void eat() {
System.out.println(" I like to eat bones !");
}
public void speak() {
System.out.println(" Wang Wang Wang !");
}
public static void main(String[] args) {
Dog d=new Dog();
d.eat();
d.speak();
}
}
  • Interfaces are written in a similar way to classes , But they belong to different concepts . Class describes the properties and methods of an object . The interface contains the methods that the class will implement .

  • The difference between interface and class :

  1. Interfaces cannot be used to instantiate objects .

  2. Interface has no constructor .

  3. All methods in an interface must be abstract methods .

  4. Interface cannot contain member variables , except static and final Variable .

  5. Interfaces need to be implemented by classes .

  6. Interface supports multiple inheritance .

3. Code example -Array

public class Array {
public static void main(String[] args) {
int[] myList = new int[] {5,2,0,1,3,1,4};
for(int list: myList) {
System.out.print(list);
}
}
}
  • In the above code ,myList Variables hold references to array objects , It's stored on the stack , The space occupied by array objects is allocated on the heap ( Just like the picture above ).

expand 1:

  • The return value type of the method is the class name : Returns the object of this class .

  • The return value type of the method is the interface name : Returns the object of the implementation class of the interface .

 public static Comparable findMax(Comparable[] arr) {
int maxIndex=0;
for(int i=1;i<arr.length;i++)
if(arr[i].compareTo(arr[maxIndex])>0)
maxIndex=i;
return arr[maxIndex];
}
  • In the above code , Pass parameters to implement Comparable An array of objects for the interface , Method returns Comparable Interface implementation class object .

  • We usually use them Object、 Interface type, etc , The goal is to support code reuse .

expand 2: Autoboxing and unboxing

  • Automatic boxing : If one int The type quantity is transferred to the need for a Integer Where the object is , The compiler will insert a pair behind the scenes Integer Call to construct method .

  • Automatic boxing : If one Integer Objects are placed where they need to be int It's the place of quantity , The compiler will insert a pair behind the scenes intValue Method call .

notes : Reference resources 《 Data structure and algorithm analysis Java Language description 》 and Novice tutorial

版权声明
本文为[The future of garlic]所创,转载请带上原文链接,感谢
https://javamana.com/2021/01/20210121223812189N.html

  1. 【计算机网络 12(1),尚学堂马士兵Java视频教程
  2. 【程序猿历程,史上最全的Java面试题集锦在这里
  3. 【程序猿历程(1),Javaweb视频教程百度云
  4. Notes on MySQL 45 lectures (1-7)
  5. [computer network 12 (1), Shang Xuetang Ma soldier java video tutorial
  6. The most complete collection of Java interview questions in history is here
  7. [process of program ape (1), JavaWeb video tutorial, baidu cloud
  8. Notes on MySQL 45 lectures (1-7)
  9. 精进 Spring Boot 03:Spring Boot 的配置文件和配置管理,以及用三种方式读取配置文件
  10. Refined spring boot 03: spring boot configuration files and configuration management, and reading configuration files in three ways
  11. 精进 Spring Boot 03:Spring Boot 的配置文件和配置管理,以及用三种方式读取配置文件
  12. Refined spring boot 03: spring boot configuration files and configuration management, and reading configuration files in three ways
  13. 【递归,Java传智播客笔记
  14. [recursion, Java intelligence podcast notes
  15. [adhere to painting for 386 days] the beginning of spring of 24 solar terms
  16. K8S系列第八篇(Service、EndPoints以及高可用kubeadm部署)
  17. K8s Series Part 8 (service, endpoints and high availability kubeadm deployment)
  18. 【重识 HTML (3),350道Java面试真题分享
  19. 【重识 HTML (2),Java并发编程必会的多线程你竟然还不会
  20. 【重识 HTML (1),二本Java小菜鸟4面字节跳动被秒成渣渣
  21. [re recognize HTML (3) and share 350 real Java interview questions
  22. [re recognize HTML (2). Multithreading is a must for Java Concurrent Programming. How dare you not
  23. [re recognize HTML (1), two Java rookies' 4-sided bytes beat and become slag in seconds
  24. 造轮子系列之RPC 1:如何从零开始开发RPC框架
  25. RPC 1: how to develop RPC framework from scratch
  26. 造轮子系列之RPC 1:如何从零开始开发RPC框架
  27. RPC 1: how to develop RPC framework from scratch
  28. 一次性捋清楚吧,对乱糟糟的,Spring事务扩展机制
  29. 一文彻底弄懂如何选择抽象类还是接口,连续四年百度Java岗必问面试题
  30. Redis常用命令
  31. 一双拖鞋引发的血案,狂神说Java系列笔记
  32. 一、mysql基础安装
  33. 一位程序员的独白:尽管我一生坎坷,Java框架面试基础
  34. Clear it all at once. For the messy, spring transaction extension mechanism
  35. A thorough understanding of how to choose abstract classes or interfaces, baidu Java post must ask interview questions for four consecutive years
  36. Redis common commands
  37. A pair of slippers triggered the murder, crazy God said java series notes
  38. 1、 MySQL basic installation
  39. Monologue of a programmer: despite my ups and downs in my life, Java framework is the foundation of interview
  40. 【大厂面试】三面三问Spring循环依赖,请一定要把这篇看完(建议收藏)
  41. 一线互联网企业中,springboot入门项目
  42. 一篇文带你入门SSM框架Spring开发,帮你快速拿Offer
  43. 【面试资料】Java全集、微服务、大数据、数据结构与算法、机器学习知识最全总结,283页pdf
  44. 【leetcode刷题】24.数组中重复的数字——Java版
  45. 【leetcode刷题】23.对称二叉树——Java版
  46. 【leetcode刷题】22.二叉树的中序遍历——Java版
  47. 【leetcode刷题】21.三数之和——Java版
  48. 【leetcode刷题】20.最长回文子串——Java版
  49. 【leetcode刷题】19.回文链表——Java版
  50. 【leetcode刷题】18.反转链表——Java版
  51. 【leetcode刷题】17.相交链表——Java&python版
  52. 【leetcode刷题】16.环形链表——Java版
  53. 【leetcode刷题】15.汉明距离——Java版
  54. 【leetcode刷题】14.找到所有数组中消失的数字——Java版
  55. 【leetcode刷题】13.比特位计数——Java版
  56. oracle控制用户权限命令
  57. 三年Java开发,继阿里,鲁班二期Java架构师
  58. Oracle必须要启动的服务
  59. 万字长文!深入剖析HashMap,Java基础笔试题大全带答案
  60. 一问Kafka就心慌?我却凭着这份,图灵学院vip课程百度云