public class LocalDate {
public static void main(String[] args) {

    LocalDateTime localDateTime = LocalDateTime.now();
    LocalDateTime plusDaysResult = localDateTime.plusDays(20L);
    System.out.println("當(dāng)前時(shí)間是 : " + localDateTime + "\n"
            + "當(dāng)前時(shí)間加20天后為 : " + plusDaysResult + "\n");


}

}

int main()
{
int x,y;
printf("請(qǐng)輸入第一個(gè)數(shù):\n");
scanf("%d",&x);
printf("請(qǐng)輸入第二個(gè)數(shù):\n");
scanf("%d",&y);
prinf("相加:%d\n",x+y);
prinf("相減:%d\n",x-y);
prinf("相乘:%d\n",x*y);
prinf("相除:%.2f\n",x/(y*1.0));//把y*1.0轉(zhuǎn)換成float類型的
printf("取余:%d",x%y);
}

package lxx;
import java.util.Scanner;

    /**
 * @author kangjiafu
 * @date 2021/5/5 20:40
 */
public class main {
        public static void main(String[] args) {
            int totalDay = 0;
            int dayOfWeek;
            int day = 0;
            int dayOfYear = 0;
            Scanner cs = new Scanner(System.in);
            System.out.print("請(qǐng)輸入年:");
            int year = cs.nextInt();
            System.out.print("請(qǐng)輸入月:");
            int month = cs.nextInt();
            boolean bool = false;

            if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
                bool = true;
            }

            for (int i = 1900; i < year; i++) {
                if (i % 4 == 0 && i % 100 != 0 || i % 400 == 0) {
                    totalDay += 366;
                } else {
                    totalDay += 365;
                }
            }
            for (int i = 1; i <= month; i++) {
                switch (i) {
                    case 1:
                    case 3:
                    case 5:
                    case 7:
                    case 8:
                    case 10:
                    case 12:
                        day = 31;
                        break;
                    case 4:
                    case 6:
                    case 9:
                    case 11:
                        day = 30;
                        break;

                    case 2:
                        if (bool) {
                            day = 29;
                            break;
                        } else {
                            day = 28;
                            break;
                        }


                }
                if (i < month) {
                    dayOfYear += day;

                }

                totalDay += dayOfYear;
                dayOfWeek = (1 + totalDay) % 7;
                System.out.println("星期天\t星期一\t星期二\t星期三\t星期四\t星期五\t星期六");

                for (int i1 = 0; i < dayOfWeek; i++) {
                    System.out.print("\t");
                }
                for (int i1 = 1; i <= day; i++) {
                if ((totalDay + i) % 7 == 6) {
                        System.out.print(i + "\n");
                    } else {
                        System.out.print(i + "\t");
                    }
                }
            }
        }
    }

public class Cat {
    String name;
    String color;
    int age;
    public void xingMing(){
        System.out.println("妮妮");
    }
    public void hanJiao(){
        System.out.println("喵");
    }
}

public class CatTest {
    public static void main(String[] args){
        Cat c=new Cat();

        c.name="妮妮";
        c.color="灰色";
        c.age=2;
        System.out.println("該貓的顏色為："+c.color);
        System.out.println("該貓的年齡為："+c.age+"歲");
        
        c.xingMing();
        c.hanJiao();
    }
}

public class main {
    private String chepaihao;
    private int chesu;
    private double zaizhong;
    public String getChepaihao() {
        return chepaihao;
    }
    public void setChepaihao(String chepaihao) {
        this.chepaihao = chepaihao;
    }
    public int getChesu() {
        return chesu;
    }
    public void setChesu(int chesu) {
        this.chesu = chesu;
    }
    public double getZaizhong() {
        return zaizhong;
    }
    public void setZaizhong(double zaizhong) {
        this.zaizhong = zaizhong;
    }
    public main()
    {
        chepaihao="XX231";
        chesu=100;
        zaizhong=100;
    }
    public main(String chepaihao, int chesu, double zaizhong) {
        super();
        this.chepaihao = chepaihao;
        this.chesu = chesu;
        this.zaizhong = zaizhong;
    }
    public void jiasu(int sudu)
    {
        if(sudu<0)
        {
            System.out.println("無法加速");
        }
        else
        {
            chesu+=sudu;
        }
    }
    public void jiansu(int sudu)
    {
        if(sudu<0)
        {
            System.out.println("無法減速");
        }

        else
        {

            if((chesu-sudu)<0)
            {
                System.out.println("減速失敗");
            }
            else
            {
                chesu-=sudu;
            }

        }
    }


}

public class che {
    public static void main(String[] args) {
        main che1=new main();
        che1.setChepaihao("豫k5651");
        che1.jiasu(30);
        System.out.println("車牌號(hào)="+che1.getChepaihao());
        System.out.println("當(dāng)前車速="+che1.getChesu());
        System.out.println("載重="+che1.getZaizhong());

        main che2=new main("豫j0394",120,200);
        che2.jiansu(20);
        System.out.println("車牌號(hào)="+che2.getChepaihao());
        System.out.println("當(dāng)前車速="+che2.getChesu());
        System.out.println("載重="+che2.getZaizhong());

    }
}

6.封裝的作用

(1)便于使用者正確使用系統(tǒng)，防止錯(cuò)誤修改屬性

(2)降低了構(gòu)建大型系統(tǒng)的風(fēng)險(xiǎn)

(3)提高程序的可重用性

(4)降低程序之間的耦合度

7.C