java对象实例化的方式

Posted 2021-01-04

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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