java建立5個類的對象_Java建立對象的5種方式

1.使用 new 關鍵字(最常用)：

objectname obj = new objectname();

2.使用反射的class類的newinstance()方法：

objectname obj = objectname.class.newinstance();

3.使用反射的constructor類的newinstance()方法：

objectname obj = objectname.class.getconstructor.newinstance();

4.使用對象克隆clone()方法：

objectname obj = obj.clone();

5.使用反序列化(objectinputstream)的readobject()方法：

objectname obj = new objectinputstream(new fileinputstream(file_name)).readobject();

代碼示例：

1.首先建立一個user類：

1 package com.example.demo.model;

2

3 import java.io.serializable;

4 import java.util.objects;

5

6 public class user implements serializable, cloneable {

7 private static final long serialversionuid = 1l;

8 private string id;

9 private string name;

10 private string phone;

11

12 public user(string id, string name, string phone) {

13 this.id = id;

14 this.name = name;

15 this.phone = phone;

16 }

17

18 public user() {

19 }

20

21 public string getid() {

22 return id;

23 }

24

25 public void setid(string id) {

26 this.id = id;

27 }

28

29 public string getname() {

30 return name;

31 }

32

33 public void setname(string name) {

34 this.name = name;

35 }

36

37 public string getphone() {

38 return phone;

39 }

40

41 public void setphone(string phone) {

42 this.phone = phone;

43 }

44

45 @override

46 public user clone() throws clonenotsupportedexception {

47 return (user) super.clone();

48 }

49

50 @override

51 public boolean equals(object o) {

52 if (this == o) return true;

53 if (o == null || getclass() != o.getclass()) return false;

54 user user = (user) o;

55 return objects.equals(id, user.id) &&

56 objects.equals(name, user.name) &&

57 objects.equals(phone, user.phone);

58 }

59

60 @override

61 public int hashcode() {

62 return objects.hash(id, name, phone);

63 }

64

65 @override

66 public string tostring() {

67 return "user{" +

68 "id='" + id + '\'' +

69 ", name='" + name + '\'' +

70 ", phone='" + phone + '\'' +

71 '}';

72 }

73 }

2.然後開始建立user對象：

1 package com.example.demo.practice;

2

3 import com.example.demo.model.user;

4

5 import java.io.fileinputstream;

6 import java.io.fileoutputstream;

7 import java.io.objectinputstream;

8 import java.io.objectoutputstream;

9

10 public class objectcreation {

11 private static final string file_name = "user.obj";

12

13 public static void main(string[] args) throws exception {

14 //方式一 使用new關鍵字

15 user user = new user("1", "張三", "135****8457");

16 system.out.println(user.tostring());

17

18 //方式二 使用class類的newinstance()方法

19 user user2 = user.class.newinstance();

20 user2.setname("李四");

21 system.out.println(user2.tostring());

22

23 //方式三 使用constructor類的newinstance()方法

24 user user3 = user.class.getconstructor().newinstance();

25 user3.setname("王五");

26 system.out.println(user3.tostring());

27

28 //方式四 使用clone()方法，前提是被克隆類必須實作cloneable接口并且重寫其clone()方法

29 user user4 = user.clone();

30 system.out.println(user4.tostring());

31 system.out.println(user == user4);

32 system.out.println(user.equals(user4));

33

34 //方式五 使用反序列化方式，調用objectinputstream對象的readobject()方法，前提是類需要實作serializable接口

35 //序列化

36 objectoutputstream oos = new objectoutputstream(new fileoutputstream(file_name));

37 oos.writeobject(user);

38 //反序列化

39 objectinputstream ois = new objectinputstream(new fileinputstream(file_name));

40 user user5 = (user) ois.readobject();

41 system.out.println(user5.tostring());

42 }

43 }

輸出結果如下：

user{id='1', name='張三', phone='135****8457'}

user{id='null', name='李四', phone='null'}

user{id='null', name='王五', phone='null'}

user{id='1', name='張三', phone='135****8457'}

false

true

user{id='1', name='張三', phone='135****8457'}

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