請定義一個交通工具(Vehicle)的類，其中有: 屬性：速度(speed)，體積(size)等等

public class Vehicle {
    double speed;
    double size;
    Vehicle(){
        speed=1.0;
        size=2.0;
    }
    void move(){    
    }
    void setSpeed(int speed){
        this.speed=speed;
    }
    void setSize(int size){
        this.size=size;
    }
    void speedUp(){
        speed=speed+1;
        System.out.println("汽車加速后的速度為"+speed+"千米/時");
    }
    void speedDown(){
        speed=speed-1;
        System.out.println("汽車減速后的速度為"+speed+"千米/時");
    }
}
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public class Test {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Vehicle aaa=new Vehicle();
        System.out.println("汽車的速度為"+aaa.speed+"千米/時");
        System.out.println("汽車的體積為"+aaa.size+"立方米");
        aaa.speedUp();
        aaa.speedDown();
    }

}