第六章 类(Class) 和对象(Object)

一、笔记导图

二、实例代码：

public class PrintCarStatus{
    public static void main(String[] args){
        int speed;
        String color;
        String name;
        String direction;
        speed = 200;
        color = "红色";
        name = "法拉利";
        direction = "纽博格林南环赛道";
        System.out.println("经过的汽车的速度为："+ speed);
        System.out.println("它的颜色是："+ color);
        System.out.println("汽车的名字叫做"+ name);
        System.out.println("汽车的行驶方向为"+ direction);
    }
}

//创建一个Car类，或定义Car类
public class Car{
    int speed;
    String name;
    String color;
    String direction;
}

public class UseCar {
    public static void main(String[] args) {
        Car carPassedBy;          //1）声明一个Car类的变量
        carPassedBy = new Car();  //2）创建一个Car类的实体
        carPassedBy.speed = 60;   //3）通过carPassedBy给Car实体的各个属性赋值
        carPassedBy.color = "红色";
        carPassedBy.name = "法拉利";
        carPassedBy.direction = "纽博格林南环赛道";
        System.out.println("经过的汽车的速度为："+ carPassedBy.speed); //4）通过carPassedBy输出Car实体的各个属性的值
        System.out.println("它的颜色是："+ carPassedBy.color);
        System.out.println("汽车的名字叫做："+ carPassedBy.name);
        System.out.println("汽车的行驶方向为："+ carPassedBy.direction);
    }
}

public class Plural{
    int realPart;    //保存复数实部的值
    int virtualPart; //保存复数虚部的值
}

public class UsePlural{
    public static void main(String[] args){
        Plural a;            //声明一个复数a
        a = new Plural();    //创建一个复数对象
        a.realPart = 5;      //给这个复数对象的realPart属性赋值
        a.virtualPart = 10;  //给这个复数对象的virtualPart属性赋值
        System.out.println("复数的实部为"+ a.realPart);
        System.out.println("复数的虚部为"+ a.virtualPart);
    }
} 

public class Driver{
    String name;  //默认值为null
    int age;  //默认缺省值为0
    Car car;  //默认值为null
}

public class PrintDriverProps{
    public static void main(String[] agrs){
        Driver driver = new Driver();
        /*System.out.println(driver.name);
        System.out.println(driver.age);
        System.out.println(driver.car); */
        System.out.println(driver.age);
        if (driver.name !=null){
            System.out.println("司机的名字为：" + driver.name);
        }else {
            System.out.println("没司机的名字");
        }
        if (driver.car !=null){
            System.out.println("司机的信息为：" + driver.car);
        }else {
            System.out.println("没司机的信息");
        }
    }
}

三、练习题