定义一个抽象类，并设计两个子类继承该抽象类，演示它们的使用。具体，定义一个类Vehicle并将它声明为抽象类。

public abstract class Test_6_1Vehicle {
    private String m;
    public abstract String InfoOfWheels();
    public String getM() {
        return m;
    }
    public void setM(String m) {
        this.m = m;
    }
}

public class Test_6_1Car extends Test_6_1Vehicle {
    @Override
    public String InfoOfWheels() {
        return "四轮车";
    }
}

public class Test_6_1Motorbike extends Test_6_1Vehicle {
    @Override
    public String InfoOfWheels() {
        return "双轮车";
    }
}

public class Test_6_1Test {
    public static void main(String[] args) {
        Test_6_1Car car = new Test_6_1Car();
        Test_6_1Motorbike motor = new Test_6_1Motorbike();
        System.out.println(car.InfoOfWheels());
        System.out.println(motor.InfoOfWheels());
    }
}