才能是来自独创性。独创性是思维、观察、理解和判断的一种独特的方式。
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一、db4o简介：
db4o 为我们带来的是这样一种面向对象的查询方式:
二、安装 |
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三、入门实例：(运行以后将在当前目录中产生db.data数据库文件)import com.db4o.Db4o;
import com.db4o.ObjectContainer;
import com.db4o.ObjectSet;
public class FirstStepsExample{
public static void main(String[] args) {
ObjectContainer db=Db4o.openFile("db.data");
try {
storeFirstPilot(db);
storeSecondPilot(db);
retrieveAllPilots(db);
retrievePilotByName(db);
retrievePilotByExactPoints(db);
updatePilot(db);
deleteFirstPilotByName(db);
deleteSecondPilotByName(db);
}
finally {
db.close();
}
}
public static void accessDb4o() {
ObjectContainer db=Db4o.openFile("db.data");
try {
// do something with db4o
}
finally {
db.close();
}
}
public static void storeFirstPilot(ObjectContainer db) {
Pilot pilot1=new Pilot("Michael Schumacher",100);
db.set(pilot1);
System.out.println("Stored "+pilot1);
}
public static void storeSecondPilot(ObjectContainer db) {
Pilot pilot2=new Pilot("Rubens Barrichello",99);
db.set(pilot2);
System.out.println("Stored "+pilot2);
}
public static void retrieveAllPilotQBE(ObjectContainer db) {
Pilot proto=new Pilot(null,0);
ObjectSet result=db.get(proto);
listResult(result);
}
public static void retrieveAllPilots(ObjectContainer db) {
ObjectSet result=db.get(Pilot.class);
listResult(result);
}
public static void retrievePilotByName(ObjectContainer db) {
Pilot proto=new Pilot("Michael Schumacher",0);
ObjectSet result=db.get(proto);
listResult(result);
}
public static void retrievePilotByExactPoints(ObjectContainer db) {
Pilot proto=new Pilot(null,100);
ObjectSet result=db.get(proto);
listResult(result);
}
public static void updatePilot(ObjectContainer db) {
ObjectSet result=db.get(new Pilot("Michael Schumacher",0));
Pilot found=(Pilot)result.next();
found.addPoints(11);
db.set(found);
System.out.println("Added 11 points for "+found);
retrieveAllPilots(db);
}
public static void deleteFirstPilotByName(ObjectContainer db) {
ObjectSet result=db.get(new Pilot("Michael Schumacher",0));
Pilot found=(Pilot)result.next();
db.delete(found);
System.out.println("Deleted "+found);
retrieveAllPilots(db);
}
public static void deleteSecondPilotByName(ObjectContainer db) {
ObjectSet result=db.get(new Pilot("Rubens Barrichello",0));
Pilot found=(Pilot)result.next();
db.delete(found);
System.out.println("Deleted "+found);
retrieveAllPilots(db);
}
public static void listResult(ObjectSet result) {
System.out.println(result.size());
while(result.hasNext()) {
System.out.println(result.next());
}
}
}
public class Pilot {
private String name;
private int points;
public Pilot(String name,int points) {
this.name=name;
this.points=points;
}
public int getPoints() {
return points;
}
public void addPoints(int points) {
this.points+=points;
}
public String getName() {
return name;
}
public String toString() {
return name+"/"+points;
}
}
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