Test.java

import java.util.Scanner;

/**
 * @Author 12629
 * @Description：
 */
public class Test {


    public static int sum(int a,int b) {
        return a+b;
    }

    public static int sum(int a,int b,int c) {
        return a+b;
    }

    public static double sum(int a,double b,int c) {
        return a+b;
    }

    public static double sum(double b,int c,int a) {
        return a+b;
    }

    public static double sum(double a,double b) {
        return a+b;
    }

    public static void main(String[] args) {
        int a = 10;
        int b = 20;
        int ret = sum(a,b);
        System.out.println(ret);

        double d1 = 12.3;
        double d2 = 12.5;
        double ret2 = sum(d1,d2);
        System.out.println(ret2);

    }

    public static void main21(String[] args) {
        int[] arr = {10, 20};
        swap(arr);
        System.out.println("arr[0] = " + arr[0] + " arr[1] = " + arr[1]);
    }

    public static void swap(int[] arr) {
        int tmp = arr[0];
        arr[0] = arr[1];
        arr[1] = tmp;
    }

    public static void swap(int a,int b) {
        int tmp = a;
        a = b;
        b = tmp;
    }

    public static void main19(String[] args) {
        int a = 10;
        int b = 20;
        System.out.println(a+" " + b);
        swap(a,b);
        System.out.println(a+" " + b);
    }

    public static int facSum(int n) {
        int sum = 0;
        for (int i = 1; i <= n ; i++) {
            sum += fac(i);
         /*   int ret = 1;
            for (int j = 1; j <= n ; j++) {
                ret *= j;
            }
            sum += ret;*/
        }
        return sum;
        //System.out.println("fsafafas");
    }
    /**
     * 求n的阶乘
     * @param n
     * @return
     */
    public static int fac(int n) {
        int ret = 1;
        for (int i = 1; i <= n ; i++) {
            ret *= i;
        }
        return ret;
    }

    public static void main18(String[] args) {
        int rt = facSum(5);
        System.out.println(rt);
    }

    public static void add2(int a,int b) {
        System.out.println(a+b);
    }

    public static void main17(String[] args) {
        int a = 10;
        int b = 20;
        System.out.println("第一次调用方法之前");
        int ret = add(a, b);
        System.out.println("第一次调用方法之后");
        System.out.println("ret = " + ret);

        System.out.println("第二次调用方法之前");
        ret = add(30, 50);
        System.out.println("第二次调用方法之后");
        System.out.println("ret = " + ret);
    }

    public static int add(int a, int b) {
        System.out.println("调用方法中 a = " + a + " b = " + b);
        return a + b;
    }

    public static void main16(String[] args) {
        Scanner scan = new Scanner(System.in);
        //整数  小数
        while(scan.hasNextLine()) {
            String n = scan.next();
            int age = scan.nextInt();
            System.out.println(n+" " +age);
        }
    }

    public static void main15(String[] args) {
        int a = 18;
        int b = 24;
        int c = a % b;//6
        while (c != 0) {
            a = b;//18
            b = c;//6
            c = a % b;//0
        }
        System.out.println(b);
    }

    public static void main13(String[] args) {
        for (int n = 1; n <= 100; n++) {
            //int n = 11;
            int i = 2;
            for (; i <= Math.sqrt(n) ; i++) {
                if(n % i == 0) {
                   // System.out.println("不是素数！");
                    break;
                }
            }
            if(i >  Math.sqrt(n)) {
                System.out.println(n+ "是素数!");
            }
        }
    }

    public static void main12(String[] args) {
        int n = 11;
        int i = 2;
        for (; i <= n/2 ; i++) {
            if(n % i == 0) {
                System.out.println("不是素数！");
                break;
            }
        }
        if(i > n/2) {
            System.out.println("是素数!");
        }
    }

    public static void main11(String[] args) {
        int n = 9;
        int i = 2;
        for (; i < n ; i++) {
            if(n % i == 0) {
                System.out.println("不是素数！");
                break;
            }
        }
        if(i == n) {
            System.out.println("是素数!");
        }
    }

    public static void main10(String[] args) {
        int n = 7;
        for (int i = 31; i >= 1 ; i -= 2) {
            System.out.print(((n>>i) & 1) +" ");
        }//偶数
        System.out.println();
        for (int i = 30; i >= 0 ; i -= 2) {
            System.out.print(((n>>i) & 1) +" ");
        }
    }

    public static void main9(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int count = 3;
        while (count != 0) {
            System.out.println("请输入你的密码，共有"+count+"次机会！");
            String pass = scanner.nextLine();
            //if(pass == "123") {//equals
            if(pass.equals("123")) {//equals
                System.out.println("登录成功！");
                break;
            }else{
                System.out.println("登录失败！");
            }
            count--;
        }
    }
    public static void main8(String[] args) {
        int n = 123;
        while (n != 0) {
            System.out.println(n%10);
            n /= 10;
        }
    }

    public static void main7(String[] args) {
        for (int i = 1; i <= 9; i++) {
            for (int j = 1; j <= i ; j++) {
                System.out.print(i+"*"+j +"="+ i*j+" ");
            }
            System.out.println();
        }
    }

    public static void main6(String[] agrs) {
        Scanner scan = new Scanner(System.in);
        while(scan.hasNextInt()) {
            int n = scan.nextInt();
            for(int i = 0;i < n;i++) {
                for(int j = 0;j < n;j++) {
                    if( (i == j) || (i+j == n-1)) {
                        System.out.print("*");
                    }else{
                        System.out.print(" ");
                    }
                }
                System.out.println();
            }
        }
    }

    public static void main5(String[] args) {
        for (int i = 1; i <= 999999; i++) {
            int count = 0;
            int tmp = i;
            int sum = 0;
            while (tmp != 0) {
                tmp /= 10;
                count++;
            }
            //count里面就存储了当前数字i是几位数
            tmp = i;
            while (tmp != 0) {
                sum += Math.pow(tmp%10,count);
                tmp /= 10;
            }
            //sum就存储了和
            if(sum == i) {
                System.out.println(i);
            }
        }
    }

    public static void main4(String[] args) {
        double sum = 0.0;
        int flg = 1;
        for (int i = 1; i <= 100 ; i++) {
            sum = sum + 1.0/i * flg;
            flg = -flg;
        }
        System.out.println(sum);
    }
    public static void main3(String[] args) {
        int n = -1;
        int count = 0;
        while (n != 0) {
            n = n & (n-1);
            count++;
        }
        System.out.println(count);
    }
    public static void main2(String[] args) {
        int n = 15;
        int count = 0;
        while (n != 0) {
            if( (n & 1) != 0) {
                count++;
            }
            n = n >>> 1;
        }
        System.out.println(count);
    }
    public static void main1(String[] args) {
        int n = -1;
        int count = 0;
        for (int i = 0; i < 32; i++) {
            if(( (n >> i)  & 1) != 0) {
                count++;
            }
        }
        System.out.println(count);
    }
}