java_croe 学习笔记之对象流 （补充1 保存对象引用）

保存对象引用：

基于前面的例子，我们现在假设每个Manager 都拥有一个秘书Employee，而且一个或者多个Manager 拥有的是同一个秘书，我们不希望保存对象流时出现这种状况， 2个manager  一个秘书employee ，保存时，一共保存了3个employee。这样的话当希望对秘书employee 作出修改时，必须找出其他拷贝对象，再逐一修改。

 

我们希望做的是只保存和恢复秘书的一个拷贝，磁盘上的对象与内存中的对象布局完全一致。称其为 持久性 。想要达到这种效果，java 使用序列化的 方法，也就是 对象序列化：

1 所有保存到磁盘的对象都有一个序列

2 当向磁盘存储一个对象时，先检查是否有相同的对象存在

3 如果有相同对象，就只需要写入 已经存储对象序列号。如果没有，写入对象数据，生成序列号。

 

看下例子： 当修改秘书employee 时，manager 中引用的 employee 同样发生改变

package twelve;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Date;
import java.util.GregorianCalendar;

/**
 * @Title ObjectFileTest.java
 * @description TODO
 * @author qinpeng
 * @date Aug 19, 2009 10:40:49 PM
 */
public class ObjectFileTest {

	public static void main(String[] args) {

		ObjectOutputStream out = null;
		ObjectInputStream in = null;

		Manager boss = new Manager("carl c", 8000, 1987, 12, 15);
		Employee harry = new Employee("harry", 5000, 1985, 8, 21);
		boss.setBonus(5000);
		boss.setSecretary(harry);
		
		Employee[] staff = new Employee[3];
		staff[0] = boss;
		staff[1] = harry;
		staff[2] = new Employee("tony", 4000, 1986, 6, 12);

		try {
			try {
				out = new ObjectOutputStream(new FileOutputStream(
						"employee.dat"));
				out.writeObject(staff);
			} finally {
				if (out != null) {
					out.close();
				}
			}
		} catch (FileNotFoundException foundE) {
			foundE.printStackTrace();
			System.err.print("employee.dat  is not found");
		} catch (IOException ioE) {
			ioE.printStackTrace();
			System.err.print("IOException of main");
		}

		try {
			try {
				in = new ObjectInputStream(new FileInputStream("employee.dat"));
				Employee[] newStaff = (Employee[]) in.readObject();
				
				newStaff[1].raiseSalary(10);
				for (Employee e : newStaff) {
					System.out.println(e);
				}
			} finally {
				if (in != null) {
					in.close();
				}
			}
		} catch (ClassNotFoundException classE) {
			classE.printStackTrace();
			System.err.print("employee.dat  is not found");
		} catch (FileNotFoundException foundE) {
			foundE.printStackTrace();
			System.err.print("employee.dat  is not found");
		} catch (IOException ioE) {
			ioE.printStackTrace();
			System.err.print("IOException of main");
		}
	}

}

class Employee implements Serializable {

	private  String name;
	//private transient String name;
	private double salary;
	private Date hireDay;

	public Employee() {
	}

	public Employee(String n, double s, int year, int month, int day) {
		name = n;
		salary = s;
		GregorianCalendar claendar = new GregorianCalendar(year, month - 1, day);
	}

	public void raiseSalary(double byPercent) {
		double raise = salary * byPercent / 100;
		salary += raise;
	}

	public String toString() {
		return getClass().getName() + "name=" +name+ "---salary=" + salary;
	}

	public String getName() {
		return name;
	}

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

	public double getSalary() {
		return salary;
	}

	public void setSalary(double salary) {
		this.salary = salary;
	}

	public Date getHireDay() {
		return hireDay;
	}

	public void setHireDay(Date hireDay) {
		this.hireDay = hireDay;
	}
}

class Manager extends Employee {

	private double bonus;
	private Employee secretary ;

	public Manager(String n, double s, int year, int month, int day) {
		super(n, s, year, month, day);
		secretary = null;
	}

	public String toString() {
		return super.toString() + "bonus=" + bonus+"-------secretary's salary = "+secretary.getSalary();
	}
	
	public void setSecretary(Employee s) {
		this.secretary = s;
	}

	public double getSalary() {
		double baseSalay = super.getSalary();
		return baseSalay + bonus;
	}

	public double getBonus() {
		return bonus;
	}

	public void setBonus(double bonus) {
		this.bonus = bonus;
	}

}

  输出：

twelve.Managername=carl c---salary=8000.0bonus=5000.0-------secretary's salary = 5500.0
twelve.Employeename=harry---salary=5500.0
twelve.Employeename=tony---salary=4000.0