while loop and branching
while loop
package com.ithema.spedkey;
public class demo6241 {
public static void main(String[] args) {
// 理解while
int i = 0;
while (i < 5){
System.out.println("Hello word");
i++;
}
}
}
while loop example
package com.ithema.loop;
public class test {
public static void main(String[] args) {
// 使用while
double peak = 8848860;
double paper = 0.1;
int i = 0;
while (paper < peak){
paper *= 2;
i++;
}
System.out.println("纸张折叠了"+i+"次");
System.out.println(paper);
}
}
do-while
package com.ithema.loop;
public class test {
public static void main(String[] args) {
// 使用do-while
int i = 0;
do{
System.out.println("Hello world");
i++;
} while (i < 3);
}
}
Execute first and judge later
package com.ithema.loop;
public class test {
public static void main(String[] args) {
// 使用do-while
int i = 0;
do{
System.out.println("Hello world");
i++;
} while (i < 3);
// 先执行 后判断
do{
System.out.println("heheheheheheh");
} while(false);
}
}
package com.ithema.loop;
public class test {
public static void main(String[] args) {
for (int i = 0; i < 3; i++) {
System.out.println("hello");
}
// 不能识别i
}
}
if branch
package com.ithema.loop;
public class test {
public static void main(String[] args) {
double t = 38.9;
if (t > 37){
System.out.println("大于37");
}
double money = 90;
if (money > 99){
System.out.println("够了");
}
else{
System.out.println("不够");
}
int score = 40;
if (score >= 90){
System.out.println("优秀");
}
else if (score >= 80){
System.out.println("良好");
}
else if (score >= 60){
System.out.println("及格");
}
else{
System.out.println("不及格");
}
// 一种情况
int a = 17;
if (a < 30) System.out.println("haha");
}
}
output
大于37
不够
不及格
haha
switch
package com.ithema.loop;
public class demo241 {
public static void main(String[] args) {
String week = "周三";
switch (week) {
case "周一":
System.out.println("周一啊");
break;
case "周二":
System.out.println("周二啊");
break;
default:
System.out.println("咋回事儿？");
}
}
}
output
咋回事儿？
Switch Notes
package com.ithema.loop;
public class demo241 {
public static void main(String[] args) {
// 支持：byte、short、int、char、string等
// 不支持double、float、long
int a = 10;
switch (a) {
case 10:
System.out.println(10);
}
// case 给出的值不允许重复，只能是字面量，不能是变量
// 不要忘记写break，否则会出现穿透
}
}
package com.ithema.loop;
public class demo241 {
public static void main(String[] args) {
// 周一打游戏
// 周二打游戏
// 周三打游戏
// 周四做饭
// 周五做饭
// 周六什么
// 周七啥
String week = "周三";
switch (week){
case "周一":
case "周二":
case "周三":
System.out.println("打游戏");
break;
case "周四":
case "周五":
System.out.println("做饭");
break;
case "周六":
System.out.println("什么");
break;
case "周天":
System.out.println("啥");
break;
default:
System.out.println("none");
}
}
}
for loop
hot key:fori + tab
package com.ithema.loop;
public class demo241 {
public static void main(String[] args) {
for (int i = 0; i < 5; i++) {
System.out.println("hello world"+i);
}
System.out.println("-------------------------");
for (int i = 2; i < 5; i++) {
System.out.println("hello world"+i);
}
System.out.println("-------------------------");
for (int i = 1; i < 15; i+=2) {
System.out.println("hello world"+i);
}
System.out.println("-------------------------");
for (int i = 1; i < 10; i+=2) {
System.out.println("hello world"+i);
i-=1;
}
}
}
output
hello world0
hello world1
hello world2
hello world3
hello world4
-------------------------
hello world2
hello world3
hello world4
-------------------------
hello world1
hello world3
hello world5
hello world7
hello world9
hello world11
hello world13
-------------------------
hello world1
hello world2
hello world3
hello world4
hello world5
hello world6
hello world7
hello world8
hello world9
Sum of the first five integers
package com.ithema.loop;
public class demo241 {
public static void main(String[] args) {
int count = 0;
for (int i = 1; i <= 5 ; i++) {
count += i;
}
System.out.println(count);
}
}