Java创建对象的4种方式

亦凉 2022-06-02 03:05 185阅读 0赞

### 使用new关键字 ###

通过new关键字直接在堆内存上创建对象，这样很方便的调用对象的有参和无参的构造函数.

Student stu1 = new Student("lihua");

### Class反射调用 ###

使用Java中反射特性，来进行对象的创建。使用`Class`类的`newInstance`方法可以调用无参的构造器来创建对象，如果是有参构造器，则需要使用`Class`的`forName`方法和`Constructor`来进行对象的创建。

Class stuClass = Class.forName("Student");
    Constructor constructor = stuClass.getConstructor(String.class);
    Student stu2 = (Student) constructor.newInstance("李四");

### 使用Clone方法 ###

使用Clone的方法：无论何时我们调用一个对象的clone方法，JVM就会创建一个新的对象，将前面的对象的内容全部拷贝进去，用clone方法创建对象并不会调用任何构造函数。要使用clone方法，我们必须先实现Cloneable接口并实现其定义的clone方法。

try
    {
        Student stu3 = (Student) stu1.clone();
        System.out.println(stu3);
    }
    catch (CloneNotSupportedException e)
    {
        e.printStackTrace();
    }

### 使用序列化 ###

一个对象实现了`Serializable`接口，就可以把对象写入到文件中，并通过读取文件来创建对象。

String path = Test.class.getClassLoader().getResource("").getPath();
    String objectFilePath = path + "out.txt";
    
    ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(objectFilePath));
    objectOutputStream.writeObject(stu2);
    
    ObjectInput objectInput = new ObjectInputStream(new FileInputStream(objectFilePath));
    Student stu4 = (Student) objectInput.readObject();

### 示例代码 ###

Student对象，实现`Cloneable`和`Serializable`接口

import java.io.Serializable;
    
    /**
     * Created by wzj on 2017/11/3.
     */
    public class Student implements Cloneable,Serializable
    {
        private String name;
    
        public Student(String name)
        {
            this.name = name;
        }
    
        /**
         * @return a clone of this instance.
         * @throws CloneNotSupportedException if the object's class does not
         *                                    support the {@code Cloneable} interface. Subclasses
         *                                    that override the {@code clone} method can also
         *                                    throw this exception to indicate that an instance cannot
         *                                    be cloned.
         * @see Cloneable
         */
        @Override
        protected Object clone() throws CloneNotSupportedException
        {
            return super.clone();
        }
    }

测试类

import java.io.*;
    import java.lang.reflect.Constructor;
    import java.lang.reflect.InvocationTargetException;
    
    /**
     * Created by wzj on 2017/11/2.
     */
    public class Test
    {
        public static void main(String[] args) throws Exception
        {
            //1、第一种方式是通过new
            Student stu1 = new Student("lihua");
            System.out.println(stu1);
    
            //2、通过java反射，静态方式
            Class stuClass = Class.forName("Student");
            Constructor constructor = stuClass.getConstructor(String.class);
            Student stu2 = (Student) constructor.newInstance("李四");
    
            System.out.println(stu2);
    
            //3、通过clone实现，必须实现Cloneable接口
            try
            {
                Student stu3 = (Student) stu1.clone();
                System.out.println(stu3);
            }
            catch (CloneNotSupportedException e)
            {
                e.printStackTrace();
            }
    
            //4、通过对象流，必须实现Serializable
            String path = Test.class.getClassLoader().getResource("").getPath();
            String objectFilePath = path + "out.txt";
    
            ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(objectFilePath));
            objectOutputStream.writeObject(stu2);
    
            ObjectInput objectInput = new ObjectInputStream(new FileInputStream(objectFilePath));
            Student stu4 = (Student) objectInput.readObject();
            System.out.println(stu4);
        }
    
    
    }