Java知识点混杂

一.Math

进行数学运算

1.1格式

Math.min();

1.2举例

1.2.1随机数

double random = Math.random();
System.out.print(random);

1.2.2对小数的处理

1.Math.floor()  向下取整

2.Math.ceil()    向上取整

3.Math.round() =Math.floor(a+0.5)

public class tiaoshiDemo {
    public static void main(String[] args) {
        double i = 3.1415926;
        System.out.println(Math.floor(i));
        System.out.println(Math.ceil(i));
        System.out.println(Math.round(i));
    }
}

二.Debug

1.设置断点

2.Debug模式

3.调试

三.3个关键字

1.break；

跳出当前循环；

2.continue;

跳过当前值；

3.return;

返回值；

四.循环迭代法

4.1求和

public static int sum(int a,int b){
        int sum = 0;
        for(int i = a; i <= b;i++){
            sum += i;
        }
        return sum;
    }

4.2阶乘

  public static int sum(int a,int b){
        int sum = 1;
        for(int i = a; i <= b;i++){
            sum *= i;
        }
        return sum;
    }

4.3计算今天是今年的第几天

import java.util.Scanner;

public class daynumber {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int year = scanner.nextInt();
        int mouth = scanner.nextInt();
        int day = scanner.nextInt();
        int sum = 0;
/*
        int year = scanner.nextInt();
        int mouth = scanner.nextInt();
        int day = scanner.nextInt();
        int sum = 0;


        for(int m = 1;m < mouth;m++){
            if((m == 1) || (m == 3) || (m == 5) || (m == 7) || ( m ==8) || (m == 10)){
                sum += 31;
            }else if((m == 4) || (m == 6) || (m == 9) || (m == 11) ){
                sum += 30;
            }else{
                sum += 28;
            }
        }

 */
        for (int m = 1; m < mouth; m++) {
            switch (m) {
                case 1:
                case 3:
                case 5:
                case 7:
                case 8:
                case 10: {
                    sum += 31;
                    break;
                }

                case 4:
                case 6:
                case 9:
                case 11: {
                    sum += 30;
                    break;
                }

                case 2:
                    sum += 28;
            }
        }

            sum += day;
            boolean f = ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0));
            if (f && mouth > 2) {
                sum = sum + 1;
            }

            System.out.println(sum);
        }
    }

4.4斐波拉且数列

import java.util.Scanner;

public class feibolaqie {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();

        Long a = 1L;
        Long b = 1L;
        Long m = 0L;
        long sum = a+b;

        for(int i = 1;i < n;i++){
            m = a + b;
            a = b;
            b = m;
            sum += m;
        }
        System.out.println("m");
        System.out.println("sum");
    }
}

4.5画三角形

public class triangleDemo {
    public static void main(String[] args) {
        int hight = 5;
        for(int i = 1; i <= hight ;i++){
            int j = 0;
            for(j = 1; j <= hight-i;j++){
                System.out.print(" ");
            }

            for(int k = 1;k <= 2*i-1;k++){
                System.out.print("*");
            }
            System.out.println();
        }
    }
}