Java 数据对象（JDO）介绍(三)

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试例
简介
下面的例子示范了JDO的基础应用。代码示范了如何向数据库添加数据和取回数据。所有的代码使用的都是SolarMetric's Kodo JDO实现。包括创建数据库的机制,使域对象类扩展PersistenceCapable接口的增强和厂商特定的PersistenceManagerFactory实现使用的都是Kodo JDO实现。其他的部分使用的是标准的JDO实现。

域对象
The samples will work with a small set of classes, which represent a Fleet of Vehicle objects. The two specific types of Vehicles defined are Bicycle and MotorVehicle. MotorVehicle objects have an Engine attribute.
例子是用了一个很小的类，这个类描述了一个Vehicle(交通工具) 对象的Fleet（车队）。Vehicle 定义了两个特定的对象Bicycle 和MotorVehicle 。MotorVehicle对象有一个Engine 属性。
域对象源代码
    /**
     * Fleet.java
     */
    package com.ociweb.jdodemo;

    import java.util.Iterator;
    import java.util.List;
    import java.util.Vector;

    public class Fleet {

        private List vehicles = new Vector();

        public void addVehicle(Vehicle vehicle) {
            vehicles.add(vehicle);
        }

        public Iterator getVehicles() {
            return vehicles.iterator();
        }

        public String toString() {
            StringBuffer buffer = new StringBuffer("Fleet:/n");
            Iterator iter = getVehicles();
            while (iter.hasNext()) {
                buffer.append("/t" + iter.next() + "/n");
            }
            return buffer.toString();
        }
    }

    /**
     * Vehicle.java
     */
    package com.ociweb.jdodemo;

    public class Vehicle {

        private int numberOfWheels;

        public Vehicle(int numberOfWheels) {
            this.numberOfWheels = numberOfWheels;
        }

        public int getNumberOfWheels() {
            return numberOfWheels;
        }
    }

    /**
     * Bicycle.java
     */
    package com.ociweb.jdodemo;

    public class Bicycle extends Vehicle {

        private String model;

        public Bicycle(String model) {
            super(2);
            this.model = model;
        }

        public String toString() {
            return "Bike: Model " + model;
        }
    }

    /**
     * MotorVehicle.java
     */
    package com.ociweb.jdodemo;

    public class MotorVehicle extends Vehicle {

        private Engine engine;

        public MotorVehicle(int numberOfWheels, Engine engine) {
            super(numberOfWheels);
            this.engine = engine;
        }

        public String toString() {
            return "MotorVehicle With " + getNumberOfWheels()
                    + " Wheels.  " + engine;
        }
    }

    /**
     * Engine.java
     */
    package com.ociweb.jdodemo;

    public class Engine {

        private int numberOfCylinders;

        public Engine(int numberOfCylinders) {
            this.numberOfCylinders = numberOfCylinders;
        }

        public int getNumberOfCylinders() {
            return numberOfCylinders;
        }

        public String toString() {
            return numberOfCylinders + " Cylinder Engine.";
        }
    }