Java创建对象的5种方式

1.使用 new 关键字（最常用）：

  objectname obj = new objectname();

2.使用反射的class类的newinstance()方法：
  objectname obj = objectname.class.newinstance();

3.使用反射的constructor类的newinstance()方法：
  objectname obj = objectname.class.getconstructor.newinstance();

4.使用对象克隆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();

 

代码示例：

1.首先创建一个user类：

 

 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.然后开始创建user对象：

 

 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关键字
15         user user = new user("1", "张三", "135****8457");
16         system.out.println(user.tostring());
17 
18         //方式二 使用class类的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类的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，前提是被克隆类必须实现cloneable接口并且重写其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，调用objectinputstream对象的readobject()方法，前提是类需要实现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 }

 

输出结果如下：

user{id='1', name='张三', phone='135****8457'}
user{id='null', name='李四', phone='null'}
user{id='null', name='王五', phone='null'}
user{id='1', name='张三', phone='135****8457'}
false
true
user{id='1', name='张三', phone='135****8457'}