目录
[2.1 if](#2.1 if)
[2.2 switch](#2.2 switch)
[2.3 if与switch区别](#2.3 if与switch区别)
[3.1 for循环](#3.1 for循环)
[3.2 while循环](#3.2 while循环)
[3.3 do-while循环](#3.3 do-while循环)
[3.4 三种循环区别](#3.4 三种循环区别)
[3.5 补充知识：死循环](#3.5 补充知识：死循环)
[3.6 补充知识：循环嵌套](#3.6 补充知识：循环嵌套)
java的关键流程控制
一、最经典的三种执行顺序
二、分支结构
2.1 if
java
package com.runa.branch;
public class IfDemo {
public static void main(String[] args) {
double money = 89.0;
if(money >= 90){
System.out.println("发红包成功了");
}
else{
System.out.println("余额不足！");
}
}
}2.2 switch
java
package com.runa.branch;
/**
目标：掌握switch使用
*/
public class SwitchDemo {
public static void main(String[] args) {
String week = "周三";
switch (week ){
case "周一":
System.out.println("埋头苦干，解决bug");
break;
case "周二":
System.out.println("请大牛程序员帮忙，解决bug");
break;
case "周三":
System.out.println("今晚啤酒、龙虾、烧烤");
break;
case "周四":
System.out.println("主动帮助信赖的女程序员");
break;
case "周五":
System.out.println("今晚吃鸡");
break;
case "周六":
System.out.println("与王婆介绍的小花吃饭");
break;
case "周日":
System.out.println("郁郁寡欢，准备上班");
break;
default:
System.out.println("你输入的星期错误");
}
}
}
穿透性简化代码
2.3 if与switch区别
三、循环结构
3.1 for循环
java
package com.runa.loop;
public class ForDemo {
public static void main(String[] args) {
// for
for(int i = 0; i < 5; i++){
System.out.println("Hello World!");
}
}
}
3.2 while循环
java
package com.runa.loop;
public class WhileDemo {
public static void main(String[] args) {
//while
int i = 0;
while(i < 5){
System.out.println("Hello World!");
i++;
}
}
}
案例：
java
package com.runa.loop;
public class WhileDemo2 {
public static void main(String[] args) {
double peakHeight = 8848860;
double paperThickness = 0.1;
// 定义纸张折叠次数
int count = 0;
while (paperThickness<peakHeight){
paperThickness = paperThickness * 2;
count++;
}
System.out.println("一共折叠"+ count + "次");
}
}3.3 do-while循环
java
package com.runa.loop;
public class DoWhileDemo {
public static void main(String[] args) {
// do =while
int i = 0;
do{
System.out.println("Hello World!");
i++;
}while(i<3);
}
}3.4 三种循环区别
3.5 补充知识：死循环
3.6 补充知识：循环嵌套
四、跳转关键字：break、continue
五、随机数Random
java
package com.runa.random;
import java.util.Random;
public class RandomDemo {
public static void main(String[] args) {
// 导包，创建一个Random对象
Random r = new Random();
//调用Random提供的功能，nextInt得到随机数
for (int i = 0; i < 15; i++) {
int data = r.nextInt(10);//0-9 （）里面直接写10 bound是自动生成的
System.out.println(data);
}
}
}
要求1-10 首先将起始段变成0，就是-1，变成0-9 nextInt(10) + 1
java
package com.runa.random;
import java.util.Random;
public class RandomDemo {
public static void main(String[] args) {
// 导包，创建一个Random对象
Random r = new Random();
for (int i = 0; i < 15; i++) {
int data2 = r.nextInt(10) + 1;
System.out.println(data2);
}
}
}扩展 1 求3-17之间的随机数，就是-3变成（0-14）+ 3，nextInt(15) + 3
扩展 2
六、案例
java
package com.runa.random;
import java.util.Random;
import java.util.Scanner;
public class RandomDemo2 {
public static void main(String[] args) {
// 1、随机产生1-100的随机数
Random r = new Random();
int luckNumber = r.nextInt(100) + 1;
// System.out.println(luckNumber);
//2、定义一个死循环让用户不断去猜测
Scanner sc = new Scanner(System.in);
while(true){
System.out.println("请输入您猜测的数字：");
int guessNumber = sc.nextInt();
//3、 判断输入数字与幸运数字
if(guessNumber > luckNumber){
System.out.println("您猜测的数字过大");
} else if (guessNumber < luckNumber) {
System.out.println("您猜测的数字过小");
}else {
System.out.println("您猜对了！");
break;
}
}
}
}