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：