java对象实例化的几种方法

Dear 丶 2022-07-13 03:55 212阅读 0赞

java对象实例化有多少种方法？一般我们常用的有这么几种

1）用类的new （）创建

2）用clone方法创建， 需要类实现 Cloneable 接口

3）用 Class.forName方法获取类，在调用类的newinstance（）方法

4）将一个对象实例化后，进行序列化，再反序列化，也可以获得一个对象（远程通信的场景下使用）

下面的例子，有两个类，一个是要操作的对象类，一个是对这个类的使用，代码如下：

User.java

package com.study.javainstance; import java.io.Serializable; public class User implements Cloneable,Serializable { //实现Serializable，才有这个 private static final long serialVersionUID = -1L; //用户名 String Name=""; //用户联系方式 String Phone=""; //用户公司 String Company=""; /* * default 方法，没有这个方法，class.forname 会报错 */ public User( ) { this.Name = "default"; this.Phone = "default"; this.Company = "default"; } public User( String name,String phone, String company ) { this.Name = name; this.Phone = phone; this.Company = company; } public String getName() { return Name; } public void setName(String name) { Name = name; } public String getPhone() { return Phone; } public void setPhone(String phone) { Phone = phone; } public String getCompany() { return Company; } public void setCompany(String company) { Company = company; } @Override public Object clone() throws CloneNotSupportedException { // TODO Auto-generated method stub return super.clone(); } public String toString(){ return "Name:"+this.Name+", Phone:"+this.Phone+", Company:"+this.Company+";"; } }

UserTest.java

package com.study.javainstance; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; public class UserTest { public static void main(String[] args) { // java 实例化1，通过new方法 System.out.println("++++++++++通过Class New（）方式实例化+++++++++++++"); User user1 = new User("Kong zi", "13800010001", "Greatwalk"); System.out.println(user1.toString()); System.out.println(); // java 实例化2，通过clone方式 System.out.println("++++++++++通过 clone（）方式实例化+++++++++++++"); try { User user2 = (User) user1.clone(); user2.setName("zhuang zi"); System.out.println(user2.toString()); System.out.println(); } catch (CloneNotSupportedException e) { e.printStackTrace(); } System.out.println("++++++++++通过Class.forName 反射方式 实例化+++++++++++++"); // java 实例化3，通过反射方式，先获取class，再获取实例 { Class<?> c1 = null; //类泛型 try { c1 = Class.forName("com.study.javainstance.User"); } catch (ClassNotFoundException e) { e.printStackTrace(); } User p1 = null; try { p1 = (User) c1.newInstance(); p1.setPhone("18600010002"); System.out.println(p1.toString()); System.out.println(); } catch (InstantiationException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IllegalAccessException e) { // TODO Auto-generated catch block e.printStackTrace(); } } //通过序列化进行对象的序列化和反序列化 System.out.println("++++++++++通过序列化和反序列化进行 实例化+++++++++++++"); try{ ObjectOutputStream out = new ObjectOutputStream (new FileOutputStream("E:/objectUser.txt")); //序列化对象 out.writeObject(user1); //"Kong zi", "13800010001", "Greatwalk" out.close(); //反序列化对象 ObjectInputStream in = new ObjectInputStream(new FileInputStream("E:/objectUser.txt")); User user4 = (User) in.readObject(); System.out.println("反序列化user：" + user4); in.close(); } catch(ClassNotFoundException e ){ e.printStackTrace(); } catch(FileNotFoundException e ){ e.printStackTrace(); } catch(IOException e ){ e.printStackTrace(); } } }

上面的例子，执行的结果如下：

\++++++++++通过Class New（）方式实例化+++++++++++++  
Name:Kong zi, Phone:13800010001, Company:Greatwalk;  
  
  
\++++++++++通过 clone（）方式实例化+++++++++++++  
Name:zhuang zi, Phone:13800010001, Company:Greatwalk;  
  
  
\++++++++++通过Class.forName 反射方式  实例化+++++++++++++  
Name:default, Phone:18600010002, Company:default;  
  
  
\++++++++++通过序列化和反序列化进行 实例化+++++++++++++  
反序列化user：Name:Kong zi, Phone:13800010001, Company:Greatwalk;