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java5种常用的创建对象的方式

2018-11-27 08:30:50来源：博客园阅读 ()

除了new可以创建对象,你还知道哪一些创建对象的方式(文中介绍了5种常用创建对象的方式,有补充请在评论区留言)

Java中5种创建对象的方法

今天来聊一聊在Java创建对象的几种方法.

使用new关键字
Class对象(有3种方式获取,任意选择一种即可)的newInstance()方法
构造函数对象的newInstance()方法
对象反序列化
Object对象的clone()方法

1.使用new关键字

这是最常用也最简单的方式,也是我们最常用的创建方式，看看下面这个例子就知道了。

 1 public class Object1 {
 2 public static void main(String[] args) {
 3 Student songyoulian = new Student("songyoulian");
 4 }
 5 }
 6 class Student{
 7 private String name;
 8 public Student(String name) {
 9 this.name = name;
10 }

View Code

2.Class对象(有3种获取Class对象的方式,任意选择一种即可)的newInstance()方法

首先我们通过Class.forName()动态的加载类的Class对象，然后通过newInstance()方法获得Student类的对象

 1 public class Object2 {
 2 public static void main(String[] args) {
 3 String className = "com.zhuhuicong.objectspeak.Student";
 4 try {
 5 Class<?> clazz = Class.forName(className);
 6 Student student = (Student) clazz.newInstance();
 7 student.setName("songyoulian");
 8 System.out.println(student);
 9 } catch (ClassNotFoundException e) {
10 e.printStackTrace();
11 } catch (IllegalAccessException e) {
12 e.printStackTrace();
13 } catch (InstantiationException e) {
14 e.printStackTrace();
15 }
16 }
17 }
18 
19 class Student{
20 private String name;
21 public void setName(String name) {
22 this.name = name;
23 }
24 }

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3.构造函数对象的newInstance()方法

类Constructor也有newInstance方法，用到了反射的知识.

 1 import java.lang.reflect.Constructor;
 2 import java.lang.reflect.InvocationTargetException;
 3 
 4 public class Object4 {
 5 public static void main(String[] args) {
 6 try {
 7 Constructor<Student> constructor = Student.class.getConstructor(String.class);
 8 Student student = constructor.newInstance("songyoulian");
 9 System.out.println(student);
10 } catch (NoSuchMethodException e) {
11 e.printStackTrace();
12 } catch (IllegalAccessException e) {
13 e.printStackTrace();
14 } catch (InstantiationException e) {
15 e.printStackTrace();
16 } catch (InvocationTargetException e) {
17 e.printStackTrace();
18 }
19 }
20 }
21 
22 class Student{
23 private String name;
24 
25 public Student(String name) {
26 this.name = name;
27 }
28 
29 @Override
30 public String toString() {
31 return "Student{" +
32 "name='" + name + '\'' +
33 '}';
34 }
35 }

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4.对象反序列化

使用反序列化来获得类的对象，要求Student类要用到序列化Serializable接口.

 1 public class Object5 {
 2 public static void main(String[] args) {
 3 //先将一个对象写出到指定文件中
 4 try {
 5 Student student = new Student("songyoylian");
 6 FileOutputStream out = null;
 7 out = new FileOutputStream("E:/object.txt");
 8 ObjectOutputStream objectOutputStream = new ObjectOutputStream(out);
 9 objectOutputStream.writeObject(student);
10 objectOutputStream.flush(); //清缓存
11 objectOutputStream.close(); //关闭流
12 } catch (FileNotFoundException e) {
13 e.printStackTrace();
14 } catch (IOException e) {
15 e.printStackTrace();
16 }
17 
18 //将对象从文件中读出来
19 FileInputStream in = null;
20 try {
21 in = new FileInputStream("E:/object.txt");
22 ObjectInputStream objectInputStream = new ObjectInputStream(in);
23 Student student2 = (Student) objectInputStream.readObject();
24 System.out.println(student2);
25 } catch (FileNotFoundException e) {
26 e.printStackTrace();
27 } catch (IOException e) {
28 e.printStackTrace();
29 } catch (ClassNotFoundException e) {
30 e.printStackTrace();
31 }
32 }
33 }
34 
35 class Student implements Serializable{
36 private String name;
37 
38 public Student(String name) {
39 this.name = name;
40 }
41 
42 @Override
43 public String toString() {
44 return "Student{" +
45 "name='" + name + '\'' +
46 '}';
47 }
48 }

View Code

5.Object对象的clone()方法

Object对象中存在clone方法，它的作用是创建一个对象的副本。要求的是Student类必须继承Cloneable方法并且重写clone()方法.

 1 public class Object6{
 2 public static void main(String[] args) {
 3 Student student = new Student("songyoulian");
 4 try {
 5 Student student2 = (Student) student.clone();
 6 System.out.println(student2);
 7 } catch (CloneNotSupportedException e) {
 8 e.printStackTrace();
 9 }
10 }
11 }
12 
13 class Student implements Cloneable{
14 private String name;
15 
16 public Student(String name) {
17 this.name = name;
18 }
19 
20 @Override
21 public String toString() {
22 return "Student{" +
23 "name='" + name + '\'' +
24 '}';
25 }
26 
27 @Override
28 protected Object clone() throws CloneNotSupportedException {
29 return super.clone();
30 }
31 }