java5种常用的创建对象的方式

除了new可以创建对象,你还知道哪一些创建对象的方式(文中介绍了5种常用创建对象的方式,有补充请在评论区留言)

Java中5种创建对象的方法

今天来聊一聊在Java创建对象的几种方法.

1. 使用new关键字
2. Class对象(有3种方式获取,任意选择一种即可)的newInstance()方法
3. 构造函数对象的newInstance()方法
4. 对象反序列化
5. Object对象的clone()方法

1.使用new关键字

这是最常用也最简单的方式,也是我们最常用的创建方式，看看下面这个例子就知道了。

public class Object1 {
public static void main(String[] args) {
Student songyoulian = new Student("songyoulian");
}
}
class Student{
private String name;
public Student(String name) {
this.name = name;
}

2.Class对象(有3种获取Class对象的方式,任意选择一种即可)的newInstance()方法

首先我们通过Class.forName()动态的加载类的Class对象，然后通过newInstance()方法获得Student类的对象

public class Object2 {
public static void main(String[] args) {
String className = "com.zhuhuicong.objectspeak.Student";
try {
Class<?> clazz = Class.forName(className);
Student student = (Student) clazz.newInstance();
student.setName("songyoulian");
System.out.println(student);
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
}
}
}

class Student{
private String name;
public void setName(String name) {
this.name = name;
}
}

3.构造函数对象的newInstance()方法

类Constructor也有newInstance方法，用到了反射的知识.

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

public class Object4 {
public static void main(String[] args) {
try {
Constructor<Student> constructor = Student.class.getConstructor(String.class);
Student student = constructor.newInstance("songyoulian");
System.out.println(student);
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
}
}

class Student{
private String name;

public Student(String name) {
this.name = name;
}

@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
'}';
}
}

4.对象反序列化

使用反序列化来获得类的对象，要求Student类要用到序列化Serializable接口.

public class Object5 {
public static void main(String[] args) {
//先将一个对象写出到指定文件中
try {
Student student = new Student("songyoylian");
FileOutputStream out = null;
out = new FileOutputStream("E:/object.txt");
ObjectOutputStream objectOutputStream = new ObjectOutputStream(out);
objectOutputStream.writeObject(student);
objectOutputStream.flush(); //清缓存
objectOutputStream.close(); //关闭流
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}

//将对象从文件中读出来
FileInputStream in = null;
try {
in = new FileInputStream("E:/object.txt");
ObjectInputStream objectInputStream = new ObjectInputStream(in);
Student student2 = (Student) objectInputStream.readObject();
System.out.println(student2);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}

class Student implements Serializable{
private String name;

public Student(String name) {
this.name = name;
}

@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
'}';
}
}

5.Object对象的clone()方法

Object对象中存在clone方法，它的作用是创建一个对象的副本。要求的是Student类必须继承Cloneable方法并且重写clone()方法.

public class Object6{
public static void main(String[] args) {
Student student = new Student("songyoulian");
try {
Student student2 = (Student) student.clone();
System.out.println(student2);
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
}
}

class Student implements Cloneable{
private String name;

public Student(String name) {
this.name = name;
}

@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
'}';
}

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