java笔记

java课堂笔记

1. 计算3/2的值
2. 计算3/0的值
3. 计算3.0/0的值
4. 计算-3/2的值
5. 计算-3/-2的值
6. 就按3/-2的值
7. 计算0-0.0的值
8. 就按-3/0.03的值
9. 回顾一下三目运算符
10. 定义一个整数变量，判断这个数是一个奇数还是偶数
11. 定义一个变量表示分数，分数>=90 -A, >=80 -B, >=70 -C, >=60 -D, <60 -E
12. 定义一个变量表示年份，判断这一年是闰年还是平年

import java.util.*;
public class A
{
    public static void main(String[] args)
    {
        System.out.println("-----------------------------------------");
        int a = 3/2;
        double b = (double)3/0;
        double c = (double)3.0/0;
        int d = -3/2;
        int e = -3/-2;
        int f = 3/-2;
        double g = 0/0.0;
        double h = -3/0.03;
        System.out.println("3/2 is: " + a);
        System.out.println("3/0 is: " + b);
        System.out.println("3.0/0 is: " + c);
        System.out.println("-3/2 is: " + d);
        System.out.println("-3/-2 is: " + e);
        System.out.println("3/-2 is: " + f);
        System.out.println("0/0.0 is: " + g);
        System.out.println("-3/0.03 is: " + h);

        
        System.out.println("-----------------------------------------");
        System.out.println("Use ternary operator:");
        int m1 = 1;
        int m2 = 2;
        int min = (m1 < m2) ? m1:m2;
        System.out.println("min is: " + min);
    
        System.out.println("-----------------------------------------");
        System.out.println("Please input a number:");
        Scanner sc = new Scanner(System.in);
        int s1 = sc.nextInt();
        if(s1 % 2 == 0) System.out.println(s1 + " is a even number.");
        else System.out.println(s1 + " is a uneven number.");
    
        
        System.out.println("-----------------------------------------");
        System.out.println("Please input your score:");
        Scanner sc2 = new Scanner(System.in);
        int s2 = sc2.nextInt();
        int temp = 0;
        if(s2 >= 90) temp = 1;
        if((s2 >= 80) && (s2 <= 90)) temp = 2;
        if((s2 >= 70) && (s2 <= 80)) temp = 3;
        if((s2 >= 60) && (s2 <= 70)) temp = 4;
        if(s2 < 60) temp = 5;
        switch (temp) {
            case 1:
                System.out.println("You got A!");
                break;

            case 2:
                System.out.println("You got B!");
                break;

            case 3:
                System.out.println("You got C!");
                break;

            case 4:
                System.out.println("You got D!");
                break;

            case 5:
                System.out.println("You got E!");
                break; 
        
            default:
                break;
        }

        System.out.println("Please input your score:");
        Scanner sc3 = new Scanner(System.in);
        double score = sc3.nextInt();
        char level = score >= 90 ? 'A' :
                    (score >= 80) && (score <= 90) ? 'B' :
                    (score >= 70) && (score <= 80) ? 'C' :
                    (score >= 60) && (score <= 70) ? 'D' : 'E';
        System.out.println("You got " + level + "!");




        System.out.println("-----------------------------------------");
        System.out.println("Common year and Leap year:");
        Scanner input = new Scanner(System.in);
        
        System.out.println("Please enter year:");
        int year = input.nextInt();
        if(year % 4 != 0 || year % 100 == 0 && year % 400 != 0) 
        {
            System.out.println(year + " is common year");
        }
        else 
        {
                System.out.println(year + " is leap year");
        }
        
    }
}

用三目运算符判断分数级别：

 

运行结果：

1. 练习九九乘法表
2. 画一个菱形
3. 设计一个游戏：共21个苹果，两个人轮流取，每人每次只可取1~4个苹果，取最后一个苹果者输。编写人机对弈程序，人先取，计算机最后要赢。

import java.util.*;
public class A
{
    public static void main(String[] args)
    {
        System.out.println("Print the multiplication table:");
        for(int i = 1;i < 10;i++)
        {
            for(int j = 1;j <= i;j++)
            {
                System.out.print(j + "*" + i + "=" + i*j + " ");
            }
            System.out.println();
                
        }

        System.out.println("--------------------------------");
        
        int a[][] =
        {
            {1, 1, 1, 2, 1, 1, 1},
            {1, 1, 2, 2, 2, 1, 1},
            {1, 2, 2, 2, 2, 2, 1},
            {2, 2, 2, 2, 2, 2, 2},
            {1, 2, 2, 2, 2, 2, 1},
            {1, 1, 2, 2, 2, 1, 1},
            {1, 1, 1, 2, 1, 1, 1},
        }; 

        


        
        for(int m=0;m<a.length;m++){
            for(int n=0;n<a[m].length;n++){
                if(a[m][n] == 1) System.out.print(" ");
                else System.out.print("*");
            }
            System.out.println();
        }

        System.out.println("--------------------------------");


        
        for (int i = 1, j = 1; i <= 9; ) {
        System.out.print(j + "*" + i + "=" + i*j + " ");
        j++;
        if (j>i) {
            System.out.print("
");
            i++;
            j = 1;
        }
    }

    

        


            
        
    }
}