java对象实例化的方式

java对象实例化的方式有以下几种： 1、使用new 2、工厂模式 3、反射 4、clone()方法 5、反序列化方式

/**

• 实现Cloneable和Serializable接口

*/ public class Book implements Cloneable, Serializable { private static final long serialVersionUID = 1L;

private Integer serialNum;	   // 序列号
private String name;	            // 图书名称

public Book() {
	System.out.println("默认构造函数");
}

public Book(Integer serialNum, String name) {
	System.out.println("带参数构造函数");
	this.serialNum = serialNum;
	this.name = name;
}

public int getSerialNum() {
	return serialNum;
}
public void setSerialNum(int serialNum) {
	this.serialNum = serialNum;
}
public String getName() {
	return name;
}
public void setName(String name) {
	this.name = name;
}

@Override
public String toString() {
	if (name == null) {
		return "书籍属性还未填写";
	}
	
	return serialNum + " : " + name;
}

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

}

class BookFactory { public static Book getInstance(Integer serialNum, String name) { return new Book(serialNum, name); } }

public class Instantiation {

// 1.通过new实例化对象
public static Book newMode() {
	System.out.println("============================================================");
	System.out.println("通过new实例化对象");
	Book book = new Book(1, "大道扬帆");
	return book;
}

// 2.通过工厂方式实例化对象，其本质还是new，但将实例化的细节交给了工厂来处理，屏蔽了和业务代码无关的功能，一定程度上实现了和业务代码的解耦
public static Book factoryMode() {
	System.out.println("============================================================");
	System.out.println("通过工厂方式实例化对象");
	return BookFactory.getInstance(2, "大道扬帆");
}

// 3.通过反射方式实例化对象
@SuppressWarnings("rawtypes")
public static Book reflectMode() throws Exception {
	System.out.println("============================================================");
	System.out.println("通过反射方式实例化对象");
	Class[] parameterTypes = new Class[] {Integer.class, String.class};
	Constructor constructor = Book.class.getConstructor(parameterTypes);
	Book book = (Book) constructor.newInstance(3, "大道扬帆");
	
	return book;
}

// 3-1.通过反射方式实例化对象还有一种方式，但本质上其实和上面的一样,但需要类本身有无参构造函数
public static Book reflectAnotherMode() throws Exception {
	System.out.println("============================================================");
	System.out.println("通过反射方式实例化对象的另外一种方式");
	Book book = (Book) Class.forName("instantiation.Book").newInstance();
	
	return book;
}

// 4.调用已存在对象的clone()方法实例化对象
public static Book cloneMode(Book book) throws Exception {
	System.out.println("============================================================");
	System.out.println("调用已存在对象的clone()方法实例化对象");
	Book newBook = (Book) book.clone();
	System.out.println("原对象和克隆对象是同一个对象吗？" + (book == newBook));
	return newBook;
}

// 5.对象序列化后可以通过反序列化创建对象
public static Book unSerializedMode() throws Exception {
	System.out.println("============================================================");
	System.out.println("对象序列化后可以通过反序列化创建对象");
	Book book = new Book(5, "大道扬帆");
	
	ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("D:/book.obj")));
	objectOutputStream.writeObject(book);
	
	ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream(new File("D:/book.obj")));
	Book newBook = (Book) objectInputStream.readObject();
	
	System.out.println("原对象和反序列化的对象是同一个吗？" + (book == newBook));
	
	return newBook;
}

public static void main(String[] args) throws Exception {
	System.out.println(Instantiation.newMode());
	System.out.println(Instantiation.factoryMode());
	System.out.println(Instantiation.reflectMode());
	System.out.println(Instantiation.reflectAnotherMode());
	
	Book book = new Book(4, "大道扬帆");
	System.out.println(Instantiation.cloneMode(book));
	
	System.out.println(Instantiation.unSerializedMode());
}

}

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