Java练习题四【函数】

目录

 

练习题36.求一个整数各位数字之和

练习题37.回文整数

练习题38.对三个数排序

练习题39.显示图案

练习题40.摄氏温度和华氏温度之间的转换

练习题41.数列求和

练习题42.估算π

练习题43.显示0和1构成的矩阵

练习题44.检测密码

练习题45.MyTriangle类

练习题46.数学：平方根的近似求法

练习题47.回文素数

练习题48.反素数

练习题49.梅森素数

练习题50.双素数

练习题51.游戏：双色子赌博

练习题52.几何问题：正多边形的面积

---

练习题36.求一个整数各位数字之和

import java.util.Scanner;
public class Demo36 {
	public static void main(String[] args) {
		Scanner scanner=new Scanner(System.in);
		System.out.print("Enter a number:");
		long number=scanner.nextLong();
		int sum=sumDigits(number);
		System.out.println(sum);
	}
	public static int sumDigits(long n){
		int sum=0;
		while(true){
			sum+=n%10;
			n=n/10;
			if(n==0){
				break;
			}
		}
		return sum;
	}
}

练习题37.回文整数

import java.util.Scanner;
public class Demo37 {
	public static void main(String[] args) {
		Scanner scanner=new Scanner(System.in);
		System.out.print("Enter a number:");
		int number=scanner.nextInt();
		System.out.println(isPailindrome(number));
	}
	public static int reverse(int number){
		String numberStr=""+number;
		String s="";
		for(int i=numberStr.length()-1;i>=0;i--){
			s+=numberStr.charAt(i);
		}
		return Integer.parseInt(s);
	}
	public static boolean isPailindrome(int number){
		return reverse(number)==number;
	}
}

练习题38.对三个数排序

import java.util.Scanner;
public class Demo38 {
	public static void main(String[] args) {
		Scanner scanner=new Scanner(System.in);
		System.out.print("Enter three numbers:");
		double num1=scanner.nextDouble();
		double num2=scanner.nextDouble();
		double num3=scanner.nextDouble();
		//最终 num1存最小值 num2存中间值 num3存最大值
		displaySortedNumbers(num1, num2, num3);
	}
	public static void displaySortedNumbers(double num1,double num2,double num3){
		double temp=0.0;
		if(num1>num2&&num1>num3){//num1最大
			temp=num3;
			num3=num1;
			num1=temp;
			if(num1>num2){
				temp=num2;
				num2=num1;
				num1=temp;
			}
		}else if(num2>num1&&num2>num3){//num2最大
			temp=num3;
			num3=num2;
			num2=temp;
			if(num1>num2){
				temp=num2;
				num2=num1;
				num1=temp;
			}
		}else if(num3>num1&&num3>num2){//num3最大
			if(num1>num2){
				temp=num2;
				num2=num1;
				num1=temp;
			}
		}
		System.out.println(num1+"<"+num2+"<"+num3);
	}
}

练习题39.显示图案

import java.util.Scanner;
public class Demo39 {
	public static void main(String[] args) {
		Scanner scanner=new Scanner(System.in);
		System.out.print("Enter the line:");
		int line=scanner.nextInt();
		displayPattern(line);
	}
	public static void displayPattern(int line){
		for(int i=1;i<=line;i++){
			for(int k=1;k<=line-i;k++){
				System.out.print("  ");
			}
			for(int j=i;j>=1;j--){
				System.out.print(j+" ");
			}
			System.out.println();
		}
	}
}

练习题40.摄氏温度和华氏温度之间的转换

public class Demo40 {
	public static void main(String[] args) {
		for(int celsius=-10;celsius<=40;celsius++){
			System.out.println(celsius+":"+celsiusToFahrenheit(celsius));
		}
	}
	public static double celsiusToFahrenheit(double celsius){
		return (9.0/5)*celsius+32;
	}
	public static double fahrenheitToCelsius(double fahrenheit){
		return (5.0/9)*(fahrenheit-32);
	}
}

练习题41.数列求和

public class Demo41 {
	public static void main(String[] args) {
		for(int i=1;i<=20;i++){
			System.out.printf("%d : %8.4f\n",i,m(i));
		}
	}
	public static double m(int i){
		double sum=0.0;
		for(int k=1;k<=i;k++){
			sum+=1.0*k/(k+1);
		}
		return sum;
	}
}

练习题42.估算π

public class Demo42 {
	public static void main(String[] args) {
		for(int i=1;i<=901;i+=100){
			System.out.println(i+":"+m(i));
		}
	}
	public static double m(int i){
		double pi=0.0;
		double flag=1.0;
		for(int k=1;k<=i;k++){
			pi+=flag/(2*k-1);
			flag=-flag;
		}
		return 4*pi;
	}
}

练习题43.显示0和1构成的矩阵

import java.util.Random;
import java.util.Scanner;
public class Demo43 {
	public static void main(String[] args) {
		Scanner scanner=new Scanner(System.in);
		System.out.print("Enter the n:");
		int n=scanner.nextInt();
		printMatrix(n);
	}
	public static void printMatrix(int n){
		Random random=new Random();//随机工具类Math.random()
		for(int i=1;i<=n;i++){
			for(int j=1;j<=n;j++){
				System.out.print(random.nextInt(2)+" ");//[0,2)
			}
			System.out.println();
		}
	}
}

练习题44.检测密码

import java.util.Scanner;
public class Demo44 {
	public static void main(String[] args) {
		Scanner scanner=new Scanner(System.in);
		System.out.print("Enter a password:");
		String password=scanner.nextLine();
		if(isPasswordValid(password)){
			System.out.println("Valid Password");
		}else{
			System.out.println("Invalid Password");
		}
	}
	public static boolean isPasswordValid(String password){
		boolean condition1=isLengthMoreThanEight(password);
		boolean condition2=isOnlyContainsLetterAndDigit(password);
		boolean condition3=isContainsMoreThanTwoDigits(password);
		if(condition1&&condition2&&condition3){
			return true;
		}else{
			return false;
		}
	}
	public static boolean isLengthMoreThanEight(String password){
		return password.length()>=8;
	}
	public static boolean isOnlyContainsLetterAndDigit(String password){
		for(int i=0;i='0'&&c<='9';
	}
	private static boolean isLetter(char c) {
		return c>='a'&&c<='z'||c>='A'&&c<='Z';
	}
	public static boolean isContainsMoreThanTwoDigits(String password){
		return getDigitCount(password)>=2;
	}
	private static int getDigitCount(String password) {
		int count=0;
		for(int i=0;i

练习题45.MyTriangle类

import java.util.Scanner;
public class Demo45 {
	public static void main(String[] args) {
		Scanner scanner=new Scanner(System.in);
		System.out.print("Enter the three side of a triangle:");
		double side1=scanner.nextDouble();
		double side2=scanner.nextDouble();
		double side3=scanner.nextDouble();
		System.out.println(area(side1,side2,side3));
	}
	public static boolean isVaild(double side1,double side2,double side3){
		if(side1+side2>side3&&side1+side3>side2&&side2+side3>side1){
			return true;
		}else{
			return false;
		}
	}
	public static double area(double side1,double side2,double side3){
		if(isVaild(side1, side2, side3)){
			double s=(side1+side2+side3)/2;
			double area=Math.sqrt(s*(s-side1)*(s-side2)*(s-side3));
			return area;
		}else{
			throw new IllegalArgumentException("三边非法！");
		}
	}
}

练习题46.数学：平方根的近似求法

import java.util.Scanner;
public class Demo46 {
	public static void main(String[] args) {
		System.out.print("Enter a number:");
		System.out.println(sqrt(new Scanner(System.in).nextLong()));
	}
	public static double sqrt(long n){
		double nextGuess=0.0;
		double lastGuess=1.0;
		while(true){
			nextGuess=(lastGuess+n/lastGuess)/2;
			if(Math.abs(nextGuess-lastGuess)<0.0001){
				break;
			}else{
				lastGuess=nextGuess;
			}
		}
		return nextGuess;
	}
}

练习题47.回文素数

public class Demo47 {
	public static void main(String[] args) {
		int count=0;
		int num=2;
		while(true){
			if(isSuShu(num)&&isHuiWen(num)){
				System.out.print(num+" ");
				count++;
				if(count%10==0){
					System.out.println();
				}
				if(count==100){
					break;
				}
			}
			num++;
		}
	}
	public static boolean isSuShu(int num){
		boolean flag=true;
		for(int i=2;i

练习题48.反素数

public class Demo48 {
	public static void main(String[] args) {
		int count=0;
		int num=2;
		while(true){
			if(isSuShu(num)&&!isHuiWen(num)&&isSuShu(reverse(num))){
				System.out.print(num+" ");
				count++;
				if(count%10==0){
					System.out.println();
				}
				if(count==100){
					break;
				}
			}
			num++;
		}
	}
	public static boolean isSuShu(int num){
		boolean flag=true;
		for(int i=2;i

练习题49.梅森素数

public class Demo49 {
	public static void main(String[] args) {
		for(int p=1;p<=31;p++){
			int num=(int) (Math.pow(2, p)-1);
			if(isSuShu(num)){
				System.out.println(p+":"+num);
			}
		}
	}
	public static boolean isSuShu(int num) {
		boolean flag=true;
		for(int i=2;i<=num/2;i++){
			if(num%i==0){
				flag=false;
				break;
			}
		}
		return flag;
	}
}

练习题50.双素数

public class Demo50 {
	public static void main(String[] args) {
		for(int i=2;i<998;i++){
			if(Demo5_18.isSuShu(i)&&Demo5_18.isSuShu(i+2)){
				System.out.println(i+":"+(i+2));
			}
		}
	}
}

练习题51.游戏：双色子赌博

public class Demo51 {
	public static void main(String[] args) {
		//1.随机生成两个点数
		//2.计算两个点数之和
			//2.1如果和为 2 3 12 lose
			//2.2如果和为 7 11 win
			//2.3如果和为 4 5 6 8 9 10 继续随机生成两个点
				//2.3.1 如果和为7 lose
				//2.3.2 如果和为上次一样 win
				//2.3.3 继续
		boolean flag=true;//代表第一次
		int lastSum=0;
		while(true){
			int p1=(int) (1+Math.random()*6);
			int p2=(int) (1+Math.random()*6);
			int sum=p1+p2;
			System.out.println("You rolled "+p1+"+"+p2+"="+sum);
			if(flag){
				if(sum==2||sum==3||sum==12){
					System.out.println("You lose");
					break;
				}else if(sum==7||sum==11){
					System.out.println("You win");	
					break;
				}else{
					System.out.println("Point is "+sum);
					lastSum=sum;
					flag=false;
				}
			}else{
				if(sum==lastSum){
					System.out.println("You win");
					break;
				}else if(sum==7){
					System.out.println("You lose");
					break;
				}else{
					System.out.println("Point is "+sum);
					lastSum=sum;
				}
			}
		}
	}
}

练习题52.几何问题：正多边形的面积

import java.util.Scanner;
public class Demo52 {
	public static void main(String[] args) {
		Scanner scanner=new Scanner(System.in);
		System.out.print("Enter the number of sides:");
		int n=scanner.nextInt();
		System.out.print("Enter the side:");
		double side=scanner.nextDouble();
		double area=area(n,side);
		System.out.println(area);
	}
	public static double area(int n,double s){
		double area=n*s*s/(4*Math.tan(Math.PI/n));
		return area;
	}
}