1. 使用new关键字
采用new关键字实例化对象是Java中最为常见的方法，下面是采用new关键字实例化对象的示例。在开始之前，我们先准备好一个Java类：Student.java。
package com.ramostear.oops;
public class Student{
private String name;
private String nickname;
public Student(){
super();
}
public Student(String name,String nickname){
this.name = name;
this.nickname = nickname;
}
public String getName(){
return name;
}
public void setName(String name){
this.name = name;
}
public String getNickname(){
return nickname;
}
public void setNickname(String nickname){
this.nickname = nickname;
}
}
接下来，我们通过new关键字来创建几个学生：
package com.ramostear.oops;
public class TestNewStudent{
public static void main(String[] args){
Student zhangsan = new Student("Zhangsan","张三");
Student lisi = new Student();
lisi.setName("Lisi");
lisi.setNickname("李四")；
}
}
2. 使用Class类的newInstance()方法
首先，我们可以通过Class.forName()方法动态加载目标类，然后再调用newInstance()方法，动态实例化对象。同理，在开始之前，我们需要准备一个目标类：Student.java。
package com.ramostear.oops;
public class Student{
private String name = "Zhangsan";
private String nickname = "张三";
public Student(){
super();
}
public Student(String name,String nickname){
super();
this.name = name;
this.nickname = nickname;
}
public String getName(){
return name;
}
public void setName(String name){
this.name = name;
}
public String getNickname(){
return nickname;
}
public void setNickname(String nickname){
this.nickname = nickname;
}
}
接下来，将演示如何通过newInstance()方法来创建新的对象：
package com.ramostear.oops;
public class TestUseNewInstanceMethod{
public static void main(String[] args){
try{
String className = "com.ramostear.oops.Student";
Class clz = Class.forName(className);
Student student = (Student) clz.newInstance();
System.out.println("student name :"+ student.getName()+", nickname: "+student.getNickname());
}catch(InstantiationException | IllegalAccessException | ClassNotFoundException e){
e.printStackTrace();
}
}
}
运行main()方法，将输出如下信息：
student name :Zhangsan, nickname:张三
3. 使用Constructor.newInstance()方法
与Class类的newInstance()方法相似，我们还可以使用java.lang.reflect.Constructor类的newInstance()方法来创建新的对象。同样，我们先准备一个目标类：
package com.ramostear.oops;
public class Student{
private String name = "Constructor";
private String nickname = "构造器";
public Student(){
super();
}
public Student(String name,String nickname){
super();
this.name = name;
this.nickname = nickname;
}
public String getName(){
return name;
}
public void setName(String name){
this.name = name;
}
public String getNickname(){
return nickname;
}
public void setNickname(String nickname){
this.nickname = nickname;
}
}
接下来，我们看看如何使用Constructor的newInstance()方法创建新的对象：
package com.ramostear.oops;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
public class UseConstructorNewInstanceMethod{
public static void main(String[] args){
Constructor<Student> studentConstructor;
try{
studentConstructor = Student.class.getConstructor();
Student student = studentConstructor.newInstance();
System.out.println("student name :"+ student.getName()+", nickname: "+student.getNickname());
}catch(InstantiationException | IllegalAccessException | IllegalArgumentException | InvocationTargetException |
NoSuchMethodException | SecurityException e){
e.printStackTrace();
}
}
}
执行main()方法，将在控制台输出如下信息：
student name:Constructor, nickname:构造器
4. 使用反序列化
如果要使用反序列化创建对象，则目标类首先要实现Serializable接口。Serializable是一个标记接口。在本次示例中，我们先创建一个Student对象，并将其保存到data.txt文件中，然后在通过反序列化操作，读取data.txt中的数据，并创建新的对象。
package com.ramostear.oops;
import java.io.Serializable;
public class Student implements Serializable{
private String name;
private String nickname;
public Student() {
super();
}
public Student(String name, String nickname) {
super();
this.name = name;
this.nickname = nickname;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getNickname() {
return nickname;
}
public void setNickname(String nickname) {
this.nickname = nickname;
}
}
接下来，将通过一个简单的示例，演示如何使用反序列化的方式创建新的对象：
package com.ramostear.oops;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
public class StudentDemo {
public static void main(String[] args) {
String filePath = "data.txt";
Student student1 = new Student("Deserialization", "反序列化");
try {
FileOutputStream fileOutputStream = new FileOutputStream(filePath);
ObjectOutputStream outputStream = new ObjectOutputStream(fileOutputStream);
outputStream.writeObject(student1);
outputStream.flush();
outputStream.close();
FileInputStream fileInputStream = new FileInputStream(filePath);
ObjectInputStream inputStream = new ObjectInputStream(fileInputStream);
Student student2 = (Student) inputStream.readObject();
inputStream.close();
System.out.println("Student name:"+student2.getName()+", nickname:"+student2.getNickname());
} catch (Exception ee) {
ee.printStackTrace();
}
}
}
执行上述代码，将在控制台输出如下信息：
Student name:Deserialization,nickname:反序列化
5. 使用对象克隆创建新的对象
clone()方法可以创建现有对象的副本，但在使用clone()方法前，需保证模板类实现了Cloneable接口，Cloneable接口也是一个标记类接口。下面是使用克隆方式创建新对象的完整示例：
package net.javaguides.corejava.oops;
import java.io.Serializable;
public class Student implements Cloneable {
private String name;
private String nickname;
public Student() {
super();
}
public Student(String name, String nickname) {
super();
this.name = name;
this.nickname = nickname;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getNickname() {
return nickname;
}
public void setNickname(String nickname) {
this.nickname = nickname;
}
public static void main(String args[]) {
Student stu1 = new Student("Clone", "克隆");
try {
Student stu2 = (Student) stu1.clone();
System.out.println("Student name :"+stu2.getName()+",nickname:"+stu2.getNickanme());
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
}
}
运行上述代码，控制台将输出如下信息：
Student name： Clone,nickname:克隆
6. 使用sun.misc.Unsafe类的allocateInstance（)方法创建对象
class Person {
private String name = "aaa";
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Person [name=" + name + "]";
}
}
public class UnsafeClassTester {
public static void main(String[] args) {
try {
java.lang.reflect.Field field = sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
field.setAccessible(true);
sun.misc.Unsafe unsafe = (sun.misc.Unsafe) field.get(null);
Person p = (Person) unsafe.allocateInstance(Person.class);
p.setName("xxxxxx");
System.out.println(p);
} catch (Exception e) {
e.printStackTrace();
}
}
}
本文标题：六种直接或间接创建Java对象的方式
本文链接：https://blog.quwenai.cn/post/8302.html
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