Java创建对象的4种方式

面试关：同学你好，请Java有几种创建对象的方式? 我这有有台 Mac ,你能否手写实现？

public class User implements Cloneable,  Serializable {


    //历史序列化对象的反序列化 版本号不一致的情况解决
    private static final long serialVersionUID = 1L;

    private String username;
    private String pwd;

    @Override
    protected User clone() throws CloneNotSupportedException {
        return (User) super.clone();
    }

    @Override
    public String toString() {
        return "User{" +
                "username='" + username + ''' +
                ", pwd='" + pwd + ''' +
                '}';
    }

    public User(String username, String pwd) {
        this.username = username;
        this.pwd = pwd;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }
}

1. Java 反序列化创建对象
   1. 先 序列化保存对象

   public class B_0622 {
       //序列化 保存对象
       public static void main(String[] args) throws IOException {
           FileOutputStream fileOutputStream = null;
           ObjectOutputStream objectOutputStream =null;
           //序列化
           try {
               fileOutputStream = new FileOutputStream("user01.object");
               objectOutputStream = new ObjectOutputStream(fileOutputStream);
               User user01=new User("ggbond","123456");
               objectOutputStream.writeObject(user01);
           } catch (FileNotFoundException e) {
               e.printStackTrace();
           } catch (IOException e) {
               e.printStackTrace();
           }finally {
               objectOutputStream.flush();
               objectOutputStream.close();
           }
       }
   }
   

   public class B_0622_1 {
       public static void main(String[] args) throws IOException, ClassNotFoundException {
           //反序列化
   
               FileInputStream fileInputStream = new FileInputStream("user01.object");
               ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
               User user = (User) objectInputStream.readObject();
               System.out.println(user.toString());
   
   
       }
   }
   

2. Java 通过 new 创建对象

    
   public class B_0622_2 {
       public static void main(String[] args) throws CloneNotSupportedException {
           User user = new User("ggbond02", "123456");
       }
   }
   

3. Java 通过 克隆创建对象

   public class B_0622_3 {
   
       public static void main(String[] args) throws CloneNotSupportedException {
           User user = new User("ggbond03", "123456");
           User user02 = user.clone();
           System.out.println(user02.toString());
       }
   }
   

4. Java通过 反射 创建对象

   public class B_0622_4 {
   
       public static void main(String[] args) throws CloneNotSupportedException, ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
   
           //01.多种获得类对象方法- 通过 User类的全路径 获得类对象 再获取类对象实例
           User user04_1 = (User) Class.forName("blog.User").getConstructor().newInstance();
           user04_1.setUsername("ggbond04_00");
           user04_1.setPwd("123456");
           System.out.println(user04_1.toString());
   
           //02.多种获得类对象方法- 通过 User类.class 调用构造器方法 获得类对象 再获取类对象实例
           User user04_2 =  User.class.getConstructor().newInstance();
           user04_2.setUsername("ggbond04_01");
           user04_2.setPwd("123456");
           System.out.println(user04_2.toString());
   
           //02.多种获得类对象方法- 通过 User类.class 直接 获得类对象 再获取类对象实例
           // jdk 9 以后就 不建议 使用 ，建议通过 上面02 构造器方法
           User user04_3 =  User.class.newInstance();
           user04_3.setUsername("ggbond04_02");
           user04_3.setPwd("123456");
           System.out.println(user04_3.toString());
   
       }
   }