Java 练习 Java学习资料

import java.util.Random; import java.util.Scanner; public class Test { //求最大值方法的重载 ： 在同一类中定义多个方法：要求不仅可以求两个整数max，还可以求三个小数的最大值 public static int maxInt(int a,int b) { return a > b ? a : b; } public static double maxDouble(double a,double b,double c) { double m = Math.max(a,b); return m > c ? m : c; } public static void main(String[] args) { System.out.println(maxInt(2,9)); System.out.println(maxDouble(2.0,3.0,6.0)); } //求和的重载： 在同一类中，分别定义两个整数和的方法，求三个小数之和的方法，并执行，求结果 public static int addInt(int a,int b) { return a + b; } public static double addDouble(double a,double b,double c) { return a + b + c; } public static void main27(String[] args) { int fun1 = addInt(1,5); double fun2 = addDouble(1.0,5.0,3.0); System.out.println(fun1); System.out.println(fun2); } //求斐波那契数列的第n项（迭代实现） public static void fit(){ Scanner scanner = new Scanner(System.in); int n = scanner.nextInt(); int a = 1; int b = 1; int c = 0; for (int i = 3; i <= n; i++) { c = a + b; a = b; b = c; } if(n <= 2) { c = 1; } System.out.println(c); } public static void main26(String[] args) { fit(); } //使用函数的最大值，创建方法求两个数的最大值max2，随后在写一个求三位数的最大值max3 //要求： 在max3这个函数中调用max2函数，来实现3个数的最大值 public static int max4(int a,int b) { return a > b ? a:b; } public static int max5(int a,int b,int c) { int j = max2(a,b); return j > c ? j:c; } public static void main25(String[] args) { int i = max5(100,2,99); System.out.println(i); } public static int max2(int a,int b) { if(a > b) { return a; } else { return b; } } public static int max3(int a,int b,int c) { int j = max2(a,b); if( j > c) { return j; } else { return c; } } public static void main24(String[] args) { int i = max3(100,2,99); System.out.println(i); } //模拟登陆 编写代码模拟密码输入的场景，最多能输入三次密码，密码正确，提示“登陆成功”，密码错误，可重新输入， //最多输入三次，三次均错，则提示退出程序。 public static void login () { Scanner scanner = new Scanner(System.in); int count = 3; while(count != 0) { String passWard = scanner.nextLine(); if(passWard.equals("123456")) { System.out.println("密码输入正确，登陆成功！"); } else { count--; System.out.println("密码输入失败！"); System.out.println("你还有" + count + "次机会"); if(count == 0) { System.out.println("退出程序！"); } } } } public static void main23(String[] args) { login(); } //猜数字游戏 :系统自动生成1-100的数字，然后用户输入一个猜测的数字，如果输入的数字比随机数小，提示“低了”如果...... public static void main22(String[] args) { Scanner scanner = new Scanner(System.in); Random random = new Random(); int ranNum = random.nextInt(100);//[1,100) //System.out.println(random); while(true) { int n = scanner.nextInt(); if(n < ranNum) { System.out.println("猜小了"); } if(n > ranNum) { System.out.println("猜大了"); } if(n == ranNum) { System.out.println("猜对了"); } } } //获取一个数二进制序列中所有偶数和奇数位，分别输出二进制序列 public static void main21(String[] args) { Scanner scanner = new Scanner(System.in); int n = scanner.nextInt(); int count = 0; for (int i = 31; i >= 1; i -= 2) { System.out.print( ((n >>> i) & 1) + " "); } System.out.println(); for (int i = 30; i >= 0; i -= 2) { System.out.print( ((n >>> i) & 1) + " "); } } //求0-999之间的所有水仙花数（水仙花数：一个三位数各个数字的立方和等于这个数本身） public static void main20(String[] args) { Scanner scanner = new Scanner(System.in); int j = scanner.nextInt(); for (int i = 0; i <= j; i++) { int n = i; int count = 0; double sum = 0; while(n != 0) { count++; n = n / 10; } n = i; while(n != 0) { sum += Math.pow(n % 10,count); n /= 10; } if(i == sum) { System.out.println(i); } } } //1-100的所有数字出现了多少个9 public static void main19(String[] args) { int count = 0; for (int i = 1; i <= 100; i++) { if(i % 10 == 9) { count++; } if(i / 10 == 9) { count++; } } System.out.println(count); } //输出一个整数的每一位 public static void func(int n) { while(n != 0) { int c = n % 10; n = n / 10; System.out.print(c + ","); } } public static void main18(String[] args) { func(125); } //实现一个两位数相加的方法 public static int add(int a,int b) { return a+b; } public static void main17(String[] args) { int ret = add(3,4); System.out.println(ret); } //计算1/1-1/2+1/3-1/4+1/5......+1/99-1/100 public static double sum () { double j = 1.0; double sum = 0; for (int i = 1; i <= 100; i++) { sum += j / i; j = -j; } return sum; } public static void main16(String[] args) { double ret = sum(); System.out.println(ret); } public static void main15(String[] args) { double j = 1.0; double sum = 0; for (int i = 1; i <= 100; i++) { sum += j / i; j = -j; } System.out.println(sum); } //写一个函数返回参数二进制中1的个数 public static void main14(String[] args) { Scanner scan = new Scanner(System.in); int n = scan.nextInt(); int count = 0; while(n != 0) { n = n & (n - 1); count++; } System.out.println(count); } public static void main13(String[] args) { Scanner scan = new Scanner(System.in); int n = scan.nextInt(); int count = 0; while(n != 0) { if((n & 1) == 1) { count++; } n = n >>> 1; } System.out.println(count); } public static void main12(String[] args) { Scanner scan = new Scanner(System.in); int n = scan.nextInt(); int count = 0; for (int i = 1; i <= 32; i++) { if(((n >>> i) & 1) ==1) { count++; } } System.out.println(count); } //求两个正整数最大公约数 public static void main11(String[] args) { Scanner scan = new Scanner(System.in); int a = scan.nextInt(); int b = scan.nextInt();