Java基础知识强化25：Java创建对象的四种方式

1. Java程序中对象的创建有四种方式：

● 调用new语句创建对象，最常见的一种

● 运用反射手段创建对象，调用java.lang.Class 或者 java.lang.reflect.Constructor 类的newInstance()实例方法

● 调用对象的clone()方法

● 运用序列化手段，调用java.io.ObjectInputStream 对象的 readObject()方法.

2. 四种方式的代码演示，如下：

（1）创建Java工程，如下：

（2）代码如下：

Person.java，如下：

 package com.himi.demo;

 public class Person implements Cloneable {

     private int age;
     private String name;

     public Person() {

     }
     public Person(int age, String name) {
         this.age = age;
         this.name = name;
     }
     public int getAge() {
         return age;
     }
     public void setAge(int age) {
         this.age = age;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }

     @Override
     protected Object clone() throws CloneNotSupportedException {
         // TODO Auto-generated method stub
         return super.clone();
     }

 }

与此同时，Person2.java，如下：

 package com.himi.demo;

 import java.io.Serializable;

 public class Person2 implements Serializable {

     private static final long serialVersionUID = 8735345334183008720L;
     private int age;
     private String name;

     public Person2() {

     }
     public Person2(int age, String name) {
         this.age = age;
         this.name = name;
     }
     public int getAge() {
         return age;
     }
     public void setAge(int age) {
         this.age = age;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }

     @Override
     public String toString() {
         // TODO Auto-generated method stub
         return "name=" + name + ", age=" + age;
     }

 }

测试类，如下：

 package com.himi.demo;

 import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.util.Date;

 public class TestDemo {

     public static void main(String[] args) throws Exception {
         //1. 使用new构造方法
         Person p1 = new Person(23,"Jack");
         System.out.println("使用new构造方法:"+p1);

         //2. 使用反射,默认调用空构造，必须实现，负责报错：InstantiationException
         Person p2 = (Person) Class.forName("com.himi.demo.Person").newInstance();
         System.out.println("使用反射:"+p2);

         //3. 使用clone,必须实现Cloneable接口,否则抛出CloneNotSupportedException
         Person p3 = (Person) p1.clone();
         System.out.println("使用clone:"+p3);

         //4. 用对象流来实现,前提是对象必须实现 Serializable
         System.out.println();
         System.out.println("----------用对象流来实现,前提是对象必须实现 Serializable---------");
         ObjectOutputStream out = new ObjectOutputStream (new FileOutputStream("p.txt"));
         //序列化对象
         Person2 obj = new Person2(24,"haobo");
         out.writeObject("你好!");
         out.writeObject(new Date());
         out.writeObject(obj);
         out.writeInt(123); //写入基本类型数据
         out.close(); 

         //反序列化对象
         ObjectInputStream in = new ObjectInputStream(new FileInputStream("p.txt")); 

         System.out.println("obj1=" + (String) in.readObject());
         System.out.println("obj2=" + (Date) in.readObject()); 

         Person2 obj1 = (Person2) in.readObject();
         System.out.println("obj1=" + obj1); 

         int num = in.readInt();
         System.out.println("num=" + num); 

         in.close();
     }

 }

运行结果，如下：