Java 中创建对象的 5 种方式！

Posted 2021-10-23 heqiyoujing

 

 

Java中有5种创建对象的方式，下面给出它们的例子还有它们的字节码

Employee类：

　　

class Employee implements Cloneable, Serializable {   
   private static final long serialVersionUID = 1L;   
   private String name;   
   public Employee() {   
       System.out.println("Employee Constructor Called...");   
   }   
   public String getName() {   
       return name;   
   }   
   public void setName(String name) {   
       this.name = name;   
   }   
   @Override   
   public int hashCode() {   
       final int prime = 31;   
       int result = 1;   
       result = prime * result + ((name == null) ? 0 : name.hashCode());   
       return result;   
   }   
   @Override   
   public boolean equals(Object obj) {   
       if (this == obj)   
           return true;   
       if (obj == null)   
           return false;   
       if (getClass() != obj.getClass())   
           return false;   
       Employee other = (Employee) obj;   
       if (name == null) {   
           if (other.name != null)   
               return false;   
       } else if (!name.equals(other.name))   
           return false;   
       return true;   
   }   
   @Override   
   public String toString() {   
       return "Employee [name=" + name + "]";   
   }   
   @Override   
   public Object clone() {   
       Object obj = null;   
       try {   
           obj = super.clone();   
       } catch (CloneNotSupportedException e) {   
           e.printStackTrace();   
       }   
       return obj;   
   }   
}

下面的Java程序中，我们将用5种方式创建Employee对象。

public class ObjectCreation {   
   public static void main(String... args) throws Exception {   
       // 1.使用new关键字
       Employee emp1 = new Employee();   
       emp1.setName("Naresh");   
       System.out.println(emp1 + ", hashcode : " + emp1.hashCode());   
       // 2.  使用Class类的newInstance方法
       Employee emp2 = (Employee) Class.forName("org.programming.mitra.exercises.Employee")   
                              .newInstance();   
       // 或者这样
       // Employee emp2 = Employee.class.newInstance();   
       emp2.setName("Rishi");   
       System.out.println(emp2 + ", hashcode : " + emp2.hashCode());   
       // 3.使用Constructor类的newInstance方法  
       Constructor<Employee> constructor = Employee.class.getConstructor();   
       Employee emp3 = constructor.newInstance();   
       emp3.setName("Yogesh");   
       System.out.println(emp3 + ", hashcode : " + emp3.hashCode());   
       // 4.使用clone方法
       Employee emp4 = (Employee) emp3.clone();   
       emp4.setName("Atul");   
       System.out.println(emp4 + ", hashcode : " + emp4.hashCode());   
       // 5.使用反序列化  
       // Serialization   
       ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("data.obj"));   
       out.writeObject(emp4);   
       out.close();   
       //Deserialization   
       ObjectInputStream in = new ObjectInputStream(new FileInputStream("data.obj"));   
       Employee emp5 = (Employee) in.readObject();   
       in.close();   
       emp5.setName("Akash");   
        //居然用对象流写入一个对象，再读出一个对象
       System.out.println(emp5 + ", hashcode : " + emp5.hashCode());   
   }   
}