方法调用小练习

1. 写⼀个函数add，接收两个整数作为参数，返回这两个整数的和

public class TestSum { public static void main(String[] args) { int sum = add(1,2); System.out.println(sum); } public static int add(int num1,int num2) { return num1 + num2; } }

2. 写⼀个函数，接收⼀个整数，输出这个整数的所有因⼦

public class TestReceive { public static void main(String[] args) { number(51); } public static int number(int num) { if(num == 0) { return 0; } else { System.out.println(1); for(int i = 2; i <= num; i++) { if(num % i == 0) { System.out.println(i); } } } return 1; } }

3. 写⼀个函数，接收⼀个整数n，输出1+2+3+…+n 的和

//写一个函数，接收一个整数n，输出1+2+3+...+n 的和 import java.util.Scanner; public class TestSum { public static void main(String[] args) { int num = number(); int result = numberSum(num); System.out.println(result); } public static int number() { Scanner input = new Scanner(System.in); System.out.println("请输入一个整数："); return input.nextInt(); } public static int numberSum(int num) { if(num == 1) { return 1; } else { return num + numberSum(num - 1); } } }

4. 写⼀个函数，接收⼀个整数参数n，输出n 个HelloWorld

import java.util.Scanner; public class Test1 { public static void main(String[] args) { int num = number(); numberSum(num); } public static int number() { Scanner input = new Scanner(System.in); System.out.println("请输入一个整数n："); return input.nextInt(); } public static int numberSum(int n) { for(int i = 1;i <= n; i++) { System.out.println("HelloWorld"); } return 1; } }

5. 写⼀个函数，接收⼀个整数，输出这个整数是⼏位数

import java.util.Scanner; public class Test2 { public static void main(String[] args) { int num = number1(); number2(num); } public static int number1() { Scanner input = new Scanner(System.in); System.out.println("请输入一个整数n："); return input.nextInt(); } public static int number2(int n) { int count = 1; while(n >= 10) { count++; n /= 10; } System.out.println(count); return 1; } }

6. 求⼀个三位数，该三位数等与其每位数字的阶乘之和

public class TestSum1 { public static void main(String[] args) { int a, b, c, i;//for循环找那个满足条件的三位数（i） for (i = 100 ; i <= 999; i++) { a = i % 10; //个位 b = i / 10 % 10; //十位 c = i / 100; //百位 if (i == factorial(a) + factorial(b) + factorial(c)) { System.out.println("其三位数是：" + i); } } } //求阶乘 public static int factorial(int num) { int sum = 1; for (int i = 1; i <= num; i++) { sum *= i; } return sum; } }

7. 验证哥德巴赫猜想：任何⼀个⼤于6的偶数，都能分解成两个质数的和。要求输⼊⼀个整数，输出这个数能被分解成哪两个质数的和

import java.util.Scanner; public class Test4 { public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.println("请输入一个整数："); int n = sc.nextInt(); for(int i = 1; i <= n/2; i++) { int j = n - i; if(primeNumbers(i) && primeNumbers(j)) { System.out.println(n + " = " + i + " + " + j); } } } public static boolean primeNumbers(int n) { boolean falg = true;//初始化falg为true if(n < 3) {//2,3为最小的质数 falg = n > 1; } for(int i = 2; i <= Math.sqrt(n); i++) {//Math.sqrt(n) 为n的开方，如16的开方为4 if(n % i == 0) { falg = false; } } return falg; } }