Java基础–循环语句及应用
前言
使用循环语句的意义：在一定条件下，重复执行某段程序，使得程序变得简洁。今天，一同学习while、do while及for循环在Java中的基本结构和应用实例吧！
一、基本结构
1.while循环
while(条件表达式){
循环体
}
实例
public void test() {
int n = 0;
while(n<10) {
System.out.print(n+" ");
n++;
}
}实例编译后的结果如下图所示：
2.do while循环
do{
循环体
}while(条件表达式);
实例
public void test(){
int a = 0;
do{
System.out.print(a+"t");
a++;
}while(a<10);
}实例编译后的结果如下图所示：
3.for循环
for(参数初始化;循环条件;改变循环变量){
循环体
}
实例
public void test() {
for(int n=1;n<10;n++) {
System.out.print(n+"t");
}
}实例编译后的结果如下图所示：、
二、循环应用实例
1.辗转相除法
public void testGongYue() {
int a = 78;
int b = 36;
while(true) {
int n = a % b;
if(n == 0) {
System.out.println("最大公约数为："+b);
break;
}
a=b;
b=n;
}
}
2.随机产生四位验证码
public void RandomTest() {
Random ran = new Random();
String s = "";
int count = 0;
while(count<4) {
char c = (char) (ran.nextInt('y'-'0')+'0');
s += c;
count++;
}
System.out.println(s);
}
3.打印三角形
（1）直角三角形
public void test() {
for(int i=0;i<5;i++) {
for(int j=0;j<=i;j++) {
System.out.print("*");
}
System.out.println();
}
}
（2）等腰三角形
public void testLoop() {
int SIZE = 6;
for (int h = 1; h <= SIZE; h++) {
for(int k=1;k<=SIZE-h;k++) {
System.out.print(" ");
}
for(int i=1;i<=2*h-1;i++) {
System.out.print("*");
}
System.out.println();
}
}
(3) 圣诞树
public void ChristmasTree() {
int SIZE = 5;
for (int h = 1; h <= SIZE; h++) {
for(int k=1;k<=SIZE-h;k++) {
System.out.print(" ");
}
for(int i=1;i<=2*h-1;i++) {
System.out.print("*");
}
System.out.println();
}
for(int t=1;t<=4;t++) {//5层圣诞树 f=2*5-1
for(int f=1;f<=9;f++) {
if((t==1&&f==2) || (t==1&&f==8)) {
System.out.print("$");
}else if(f>=4 && f<=6) {
System.out.print("|");
}else {
System.out.print(" ");
}
}
System.out.println();
}
}
4.找出1-1000以内的素数
public void test() {
for (int i = 1; i < 1000; i++) {
boolean flag = true;
for (int j = 2; j < i; j++) {
flag = false;
if(i%j == 0) {
flag = true;
break;
}
}
if(flag == false) {
System.out.print(i+"t");
}
}
}运行结果部分截图：
5.判断某年某月某天是该年的第多少天
public void daysTest() {
Scanner sc = new Scanner(System.in);
System.out.print("请输入年份：");
int year = sc.nextInt();
System.out.print("请输入月份：");
int month = sc.nextInt();
System.out.print("请输入日子：");
int day = sc.nextInt();
/*
* 是否为闰年
*/
boolean isLeap = (year % 400 == 0) || year % 4 == 0 && year % 100 != 0;
int days = 0;
for(int m =1; m <month;m++) {
if(m==1||m==3||m==5|m==7||m==8||m==10||m==12) {
days+=31;
}else if(m==2) {
days+=28;
}else {
days+=30;
}
}
days+=day;
if(month>2 && isLeap) {
days+=1;
}
System.out.println(year+"-"+month+"-"+day+"是今年的第"+days+"天");
}
6.学生成绩管理
循环输入学生成绩，如果学生成绩在90~100为 A， 80~89为B， 60~79为C，60分以下为不及格。
编码实现如下功能：
- 统计学生的总成绩
- 统计学生的平均成绩
- 统计成绩为A，B，C，和不及格人数
- 计算A，B，C，D人数占总考试人数的比例。
public void test() {
double sum = 0 ; //总成绩
double average = 0;//平均成绩
int count1 = 0,count2 = 0,count3 = 0,count4 = 0;//各成绩等级的人数
int p = 0;//考试总人数
double r1 = 0,r2 = 0,r3 = 0,r4 = 0;//各成绩等级的比率
Scanner sc = new Scanner(System.in);
boolean flag = true;
while (flag) {
System.out.print("请输入学生的成绩：");
double score = Double.parseDouble(sc.nextLine());
p += 1;
if (score >= 90 && score <= 100) {
//System.out.println("该同学成绩为A！");
count1 += 1;
} else if (score >= 80 && score <= 89) {
//System.out.println("该同学成绩为B！");
count2 += 1;
} else if (score >= 60 && score <= 79) {
//System.out.println("该同学成绩为C！");
count3 += 1;
} else {
//System.out.println("该同学成绩不及格！");
count4 += 1;
}
sum += score;
average = sum/score;
r1 = (double)count1/p;
r2 = (double)count2/p;
r3 = (double)count3/p;
r4 = (double)count4/p;
while (flag) {
System.out.println("结束请输入-1");
int x = Integer.parseInt(sc.nextLine());
if (x != -1) {
break;
} else {
flag = false;
System.out.println("已退出！");
//System.out.println("你的输入不合法！");
}
}
}
System.out.println("同学们的总成绩为："+sum);
System.out.println("同学们的平均成绩为："+average);
System.out.println("成绩为A等的同学人数:"+count1+","+"成绩为B等的同学人数:"+count2+","
+"成绩为C等的同学人数:"+count3+","+"成绩不及格的人数："+count4);
System.out.println("成绩A等占总人数的"+r1);
System.out.println("成绩B等占总人数的"+r2);
System.out.println("成绩C等占总人数的"+r3);
System.out.println("成绩不及格等占总人数的"+r4);
}运行结果部分截图：
7.小型计算机系统
public void demo1() throws InterruptedException {
Scanner sc = new Scanner(System.in);
final String PLUS = "1";
final String SUB = "2";
final String MUL = "3";
final String DIVI = "4";
final String POW = "5";
final String MOD = "6";
final String SQRT = "7";
final String EVEN = "8";
final String MAX = "9";
final String SORT_MAX_TO_MIN = "10";
final String TRIANGLE = "11";
final String NINE_TIMES_NINE = "12";
final String EXIT = "0";
final int EVEN_FLAG = 2;
boolean f = true;
int a = 0,b = 0;
double x = 0,y =0 ;
while (f) {
System.out.println("-------------------------------");
System.out.println("1.加法t 2.减 法t ");
System.out.println("3.乘法t 4.除 法t ");
System.out.println("5.幂 t 6.取模t ");
System.out.println("7.开 方t 8.是否为偶数t ");
System.out.println("9.最大值t 10.从大至小排序t ");
System.out.println("11.等腰三角形t 12.九九乘法表t ");
System.out.println("0.退出");
System.out.println("-------------------------------");
System.out.println("请选择运算方式");
String choice = sc.nextLine();
switch (choice) {
case EXIT:
f = false;
System.out.println("系统正在退出中，请稍候！");
for (int i = 0; i < 10; i++) {
System.out.print(".");
Thread.sleep(100);
}
System.out.println("n系统已退出,谢谢使用！");
break;
case PLUS:
System.out.println("请输入数字a:");
a = Integer.parseInt(sc.nextLine());
System.out.println("请输入数字b:");
b = Integer.parseInt(sc.nextLine());
int sum = a + b;
System.out.println(a + "+" + b + "=" + sum);
break;
case SUB:
System.out.println("请输入数字a:");
a = Integer.parseInt(sc.nextLine());
System.out.println("请输入数字b:");
b = Integer.parseInt(sc.nextLine());
int sub = a - b;
System.out.println(a + "-" + b + "=" + sub);
break;
case MUL:
System.out.println("请输入数字am:");
a = Integer.parseInt(sc.nextLine());
System.out.println("请输入数字b:");
b = Integer.parseInt(sc.nextLine());
int mul = a * b;
System.out.println(a + "*" + b + "=" + mul);
break;
case DIVI:
System.out.println("请输入除数x:");
x = Double.parseDouble(sc.nextLine());
System.out.println("请输入被除数y:");
y = Double.parseDouble(sc.nextLine());
if (y != 0) {
double d = x / y;
System.out.println(x + "➗" + y + "=" + d);
} else {
System.out.println("被除数不能为0");
}
break;
case POW:
System.out.println("请输入数字x:");
x = Double.parseDouble(sc.nextLine());
System.out.println("请输入数字y:");
y = Double.parseDouble(sc.nextLine());
int result = (int) Math.pow(x, y);
System.out.println(x + "^" + y + "=" + result);
break;
case MOD:
System.out.println("请输入数字x:");
x = Double.parseDouble(sc.nextLine());
System.out.println("请输入数字y:");
y = Double.parseDouble(sc.nextLine());
double result1 = x % y;
System.out.println(x + "%" + y + "=" + result1);
break;
case SQRT:
System.out.println("请输入数字x:");
x = Double.parseDouble(sc.nextLine());
double result2 = Math.sqrt(x);
System.out.println(x + "开方的结果：" + result2);
break;
case EVEN:
System.out.println("请输入数字a:");
a = Integer.parseInt(sc.nextLine());
if (a % EVEN_FLAG == 0) {
System.out.println(a + "是偶数");
} else {
System.out.println(a + "不是偶数");
}
break;
case MAX:
System.out.println("请输入数字a:");
a = Integer.parseInt(sc.nextLine());
System.out.println("请输入数字b:");
b = Integer.parseInt(sc.nextLine());
// int max = Math.max(a, b);
System.out.println(a + "和" + b + "之间的最大值为：" + Math.max(a, b));
break;
case SORT_MAX_TO_MIN:
System.out.println("请输入数字a:");
a = Integer.parseInt(sc.nextLine());
System.out.println("请输入数字b:");
b = Integer.parseInt(sc.nextLine());
int max = Math.max(a, b);
int min = Math.min(a, b);
System.out.println("由大到小排序为:" + max + " ," + min);
break;
case TRIANGLE:
System.out.print("请输入打印三角形的层数：");
int size = Integer.parseInt(sc.nextLine());
for (int h = 1; h <= size; h++) {
for (int j = 1; j <= size - h; j++) {
System.out.print(" ");
}
for (int i = 1; i <= 2 * h - 1; i++) {
System.out.print("*");
}
System.out.println();
}
break;
case NINE_TIMES_NINE:
for (int i = 1; i < 10; i++) {
for (int j = 1; j <= i; j++) {
System.out.print(j + "*" + i + "=" + (i * j) + "t");
}
System.out.println();
}
break;
default:
boolean flag = true;
while (flag) {
System.out.println("输入不合法，请使用Y或N：");
String s = sc.nextLine();
if ("Y".equals(s) || "y".equals(s)) {
break;
} else if ("N".equals(s) || "n".equals(s)) {
flag=false;
System.out.println("系统正在退出中，请稍候！");
for (int i = 0; i < 10; i++) {
System.out.print(".");
Thread.sleep(100);
}
System.out.println("n系统已退出,谢谢使用！");
} else {
System.out.println("请重新输入Y[继续]或N[结束]：");
}
}
}
}
}运行结果部分截图：
8.掷色子游戏
/**
* 3个筛子共同掷出6，程序结束
* 1次免费 1-5次 2块 6-10次 20块 10次以上 40块
* @throws InterruptedException
*/
public void looptest1() throws InterruptedException {
Random ran = new Random();
int count = 0;
double money = 12500.00;
int win = 0;//赢人数
int lose = 0;//输人数
for (int i = 0; i < 10; i++) {
while (true) {
int a = ran.nextInt(6) + 1; //ran.nextInt(n) --> [0,n)
int b = ran.nextInt(6) + 1;
int c = ran.nextInt(6) + 1;
//System.out.println("[" + a + "," + b + "," + c + "]");
count++;
if (count == 1) {
money -= 0;
} else if (count <= 5) {
money -= 2;
} else if (count <= 10) {
money -= 20;
} else {
money -= 40;
}
//Thread.sleep(100);
if (a == 6 && b == 6 && c == 6) {
System.out.println("第"+(i+1)+"人游戏结束！");
System.out.println("第"+(i+1)+"人共掷出" + count + "次筛子");
double p = 1.0 / count * 100;
System.out.println("第"+(i+1)+"人中奖概率为：" + p);
money += 3000;
System.out.println("第"+(i+1)+"人余额为：" + money);
if(money >= 10000) {
win +=1;
}else {
lose +=1;
}
break;
}
}
}
System.out.println("赢的人数为："+win);
System.out.println("输的人数为："+lose);
}运行结果部分截图：
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