Java日志第47天 2020.8.22

例3.2 输出单个字符

public class Demo3_2 {
    public static void main(String[] args) {
        char a, b, c;
        a='B';
        b='O';
        c='Y';
        System.out.print(a);
        System.out.print(b);
        System.out.print(c);
        System.out.println();

        System.out.print((char) 66);
        System.out.print((char) 79);
        System.out.print((char) 89);
        System.out.print((char) 10);
    }
}

 

例3.3 输入单个字符

import java.util.Scanner;

public class Demo3_3 {
    public static void main(String[] args) {
        char c;
        Scanner sc = new Scanner(System.in);
        c = sc.next().charAt(0);
        System.out.println((char)(c+32));
    }
}

 

 

 

 

 

例3.4 输入输出

public class Demo3_4 {
    public static void main(String[] args) {
        int a;
        float b;
        char c;
        Scanner sc = new Scanner(System.in);
        a = sc.nextInt();
        b = sc.nextFloat();
        c = sc.next().charAt(0);

        System.out.println("a="+a+",b="+b+",c="+c);
    }
}

 

 

 

例3.5 求一元二次方程式ax² + bx+c=0的根。a, b, c的值在运行时由键盘输入，它们的值满足b²-4ac≥0。

 

import java.util.Scanner;

public class Demo3_5 {
    public static void main(String[] args) {
        float a, b, c, x1, x2;
        Scanner sc = new Scanner(System.in);
        a = sc.nextFloat();
        b = sc.nextFloat();
        c = sc.nextFloat();

        x1 = (float) ((-b + Math.sqrt(b*b-4*a*c))/(2*a));
        x2 = (float) ((-b - Math.sqrt(b*b-4*a*c))/(2*a));

        System.out.println("x1 = "+x1);
        System.out.println("x2 = "+x2);

    }
}

 

 

 

例3.6 求三角形面积

import java.util.Scanner;

public class Demo3_6 {
    public static void main(String[] args) {
        double a, b, c;
        System.out.println("Please enter a, b, c:");
        Scanner sc = new Scanner(System.in);

        a = sc.nextDouble();
        b = sc.nextDouble();
        c = sc.nextDouble();

        if(a+b>c && b+c>a && c+a>b) {
            double s, area;
            s = (a+b+c)/2;
            area = Math.sqrt(s*(s-a)*(s-b)*(s-c));
            System.out.println("area = "+area);

        } else
            System.out.println("It is not a trilateral!");
    }
}

 

 

例3.7 输入一个字符，判断它是否为大写字母，如果是，将它转换成小写字母；如果不是，不转换。然后输出最后得到的字符

import java.util.Scanner;

public class Demo3_7 {
    public static void main(String[] args) {
        char ch;
        Scanner sc = new Scanner(System.in);

        ch = sc.next().charAt(0);
        ch = (ch >= 'A'&&ch<='Z')?(char)(ch+32):ch;
        System.out.println(ch);
    }
}

 

 

 

例3.8 编写程序，判断某一年是否为闰年

import java.util.Scanner;

public class Demo3_8 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int year;
        boolean leap;
        System.out.println("Please enter year:");

        year = sc.nextInt();

        if(year%4 ==0){
            if(year%100 == 0){
                if(year%400 == 0){
                    leap = true;
                } else
                    leap =false;
            } else
                leap =false;
        } else
            leap = false;
        if(leap)
            System.out.print(year+" is");
        else
            System.out.print(year+" is not");

        System.out.println(" a leap year.");


    }
}

 

 

 

import java.util.Scanner;

public class Demo3_9 {
    public static void main(String[] args) {
        int c,s;
        float p, w, d = 0, f;
        System.out.print("Please enter p, w, s:");
        Scanner sc = new Scanner(System.in);
        p = sc.nextInt();
        w = sc.nextInt();
        s = sc.nextInt();

        if(s >=3000)
            c = 12;
        else
            c = s/250;

        switch (c) {
            case 0:d=0;break;
            case 1:d=2;break;
            case 2:
            case 3:d=5;break;
            case 4:
            case 5:
            case 6:
            case 7:d=8;break;
            case 8:
            case 9:
            case 10:
            case 11:d=10;break;
        }

        f = (float) (p*w*s*(1-d/100.0));
        System.out.println("freight="+f);
    }
}

 

 

例3.10 求1+2+3+...+100的值

public class Demo3_10 {
    public static void main(String[] args) {
        int i =1;
        int sum = 0;
        while (i<=100){
            sum = sum + i;
            i++;
        }
        System.out.println("sum="+sum);
    }
}