Java中的While和DoWhile 循环
作者：互联网
While循环
- while是最基本的循环,它的结构为:
while (布尔表达式){
//循环内容
}
- 只要布尔表达式为true,循环就会一直执行下去。
- 我们大多数情况是会让循环停止下来的,我们需要一个让表达式失效的方式来结束循环。
- 少部分情况需要循环一直执行,比如服务器的请求响应监听等。
- 循环条件一直为true就会造成无限循环【死循环】 ,我们正常的业务编程中应该尽量避免死循环。会影响程序性能或者造成程序卡死奔溃!
while代码一:
package com.kuang.struct;
public class WhileDemon01 {
public static void main(String[] args) {
//输出1~5
int i = 0;
while (i<5){
i++;
System.out.println(i);
}
}
}
运行结果一:
D:\environment\java\jdk1.8\bin\java.exe "-javaagent:D:\IntelliJ IDEA 2020.3.2\lib\idea_rt.jar=64102:D:\IntelliJ IDEA 2020.3.2\bin" -Dfile.encoding=UTF-8 -classpath D:\environment\java\jdk1.8\jre\lib\charsets.jar;D:\environment\java\jdk1.8\jre\lib\deploy.jar;D:\environment\java\jdk1.8\jre\lib\ext\access-bridge-64.jar;D:\environment\java\jdk1.8\jre\lib\ext\cldrdata.jar;D:\environment\java\jdk1.8\jre\lib\ext\dnsns.jar;D:\environment\java\jdk1.8\jre\lib\ext\jaccess.jar;D:\environment\java\jdk1.8\jre\lib\ext\jfxrt.jar;D:\environment\java\jdk1.8\jre\lib\ext\localedata.jar;D:\environment\java\jdk1.8\jre\lib\ext\nashorn.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunec.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunjce_provider.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunmscapi.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunpkcs11.jar;D:\environment\java\jdk1.8\jre\lib\ext\zipfs.jar;D:\environment\java\jdk1.8\jre\lib\javaws.jar;D:\environment\java\jdk1.8\jre\lib\jce.jar;D:\environment\java\jdk1.8\jre\lib\jfr.jar;D:\environment\java\jdk1.8\jre\lib\jfxswt.jar;D:\environment\java\jdk1.8\jre\lib\jsse.jar;D:\environment\java\jdk1.8\jre\lib\management-agent.jar;D:\environment\java\jdk1.8\jre\lib\plugin.jar;D:\environment\java\jdk1.8\jre\lib\resources.jar;D:\environment\java\jdk1.8\jre\lib\rt.jar;E:\桌面\java学习\production\基础语法 com.kuang.struct.WhileDemon01
1
2
3
4
5
Process finished with exit code 0
while的死循环代码二:
package com.kuang.struct;
public class WhileDemon02 {
public static void main(String[] args) {
//死循环 避免死循环
while(true){
//等待客户端链接
//定时检查
//.......
}
}
}
while代码三:
package com.kuang.struct;
public class WhileDemon03 {
public static void main(String[] args) {
//计算1+2+3+.....+100=?
int i = 0; //初始值
int sum=0; //和
while (i<101){
sum = sum +i;
i++;
}
System.out.println("1+2+....+100="+sum);
}
}
while运行结果三:
D:\environment\java\jdk1.8\bin\java.exe "-javaagent:D:\IntelliJ IDEA 2020.3.2\lib\idea_rt.jar=64176:D:\IntelliJ IDEA 2020.3.2\bin" -Dfile.encoding=UTF-8 -classpath D:\environment\java\jdk1.8\jre\lib\charsets.jar;D:\environment\java\jdk1.8\jre\lib\deploy.jar;D:\environment\java\jdk1.8\jre\lib\ext\access-bridge-64.jar;D:\environment\java\jdk1.8\jre\lib\ext\cldrdata.jar;D:\environment\java\jdk1.8\jre\lib\ext\dnsns.jar;D:\environment\java\jdk1.8\jre\lib\ext\jaccess.jar;D:\environment\java\jdk1.8\jre\lib\ext\jfxrt.jar;D:\environment\java\jdk1.8\jre\lib\ext\localedata.jar;D:\environment\java\jdk1.8\jre\lib\ext\nashorn.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunec.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunjce_provider.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunmscapi.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunpkcs11.jar;D:\environment\java\jdk1.8\jre\lib\ext\zipfs.jar;D:\environment\java\jdk1.8\jre\lib\javaws.jar;D:\environment\java\jdk1.8\jre\lib\jce.jar;D:\environment\java\jdk1.8\jre\lib\jfr.jar;D:\environment\java\jdk1.8\jre\lib\jfxswt.jar;D:\environment\java\jdk1.8\jre\lib\jsse.jar;D:\environment\java\jdk1.8\jre\lib\management-agent.jar;D:\environment\java\jdk1.8\jre\lib\plugin.jar;D:\environment\java\jdk1.8\jre\lib\resources.jar;D:\environment\java\jdk1.8\jre\lib\rt.jar;E:\桌面\java学习\production\基础语法 com.kuang.struct.WhileDemon03
1+2+....+100=5050
Process finished with exit code 0
do…while循环
- 对于while语句而言,如果不满足条件,则不能进入循环。但有时候我们需要即使不满足条件,也至少执行一次。
- do…while循环和while循环相似,不同的是, do…while循环至少会执行一次。
- 语法
do {
//代码语句
}while(布尔表达式);
While和do-While的区别:
- while先判断后执行。dowhile是先执行后判断!
- Do…while总是保证循环体会被至少执行一次!这是他们的主要差别。
DoWhile代码一:
package com.kuang.struct;
public class DoWhileDemon01 {
public static void main(String[] args) {
int i = 0;
int sum = 0;
do {
sum = sum + i;
i++;
}while (i<=100);
System.out.println(sum);
}
}
DoWhile运行结果一:
D:\environment\java\jdk1.8\bin\java.exe "-javaagent:D:\IntelliJ IDEA 2020.3.2\lib\idea_rt.jar=64355:D:\IntelliJ IDEA 2020.3.2\bin" -Dfile.encoding=UTF-8 -classpath D:\environment\java\jdk1.8\jre\lib\charsets.jar;D:\environment\java\jdk1.8\jre\lib\deploy.jar;D:\environment\java\jdk1.8\jre\lib\ext\access-bridge-64.jar;D:\environment\java\jdk1.8\jre\lib\ext\cldrdata.jar;D:\environment\java\jdk1.8\jre\lib\ext\dnsns.jar;D:\environment\java\jdk1.8\jre\lib\ext\jaccess.jar;D:\environment\java\jdk1.8\jre\lib\ext\jfxrt.jar;D:\environment\java\jdk1.8\jre\lib\ext\localedata.jar;D:\environment\java\jdk1.8\jre\lib\ext\nashorn.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunec.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunjce_provider.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunmscapi.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunpkcs11.jar;D:\environment\java\jdk1.8\jre\lib\ext\zipfs.jar;D:\environment\java\jdk1.8\jre\lib\javaws.jar;D:\environment\java\jdk1.8\jre\lib\jce.jar;D:\environment\java\jdk1.8\jre\lib\jfr.jar;D:\environment\java\jdk1.8\jre\lib\jfxswt.jar;D:\environment\java\jdk1.8\jre\lib\jsse.jar;D:\environment\java\jdk1.8\jre\lib\management-agent.jar;D:\environment\java\jdk1.8\jre\lib\plugin.jar;D:\environment\java\jdk1.8\jre\lib\resources.jar;D:\environment\java\jdk1.8\jre\lib\rt.jar;E:\桌面\java学习\production\基础语法 com.kuang.struct.DoWhileDemon01
5050
Process finished with exit code 0
DoWhile代码二:
package com.kuang.struct;
public class DoWhileDemon02 {
public static void main(String[] args) {
int a = 0;
while (a<0){
System.out.println(a);
a++;
}
System.out.println("=============================");
do {
System.out.println(a);
a++;
}while (a<0);
}
}
DoWhile运行结果二:
D:\environment\java\jdk1.8\bin\java.exe "-javaagent:D:\IntelliJ IDEA 2020.3.2\lib\idea_rt.jar=64377:D:\IntelliJ IDEA 2020.3.2\bin" -Dfile.encoding=UTF-8 -classpath D:\environment\java\jdk1.8\jre\lib\charsets.jar;D:\environment\java\jdk1.8\jre\lib\deploy.jar;D:\environment\java\jdk1.8\jre\lib\ext\access-bridge-64.jar;D:\environment\java\jdk1.8\jre\lib\ext\cldrdata.jar;D:\environment\java\jdk1.8\jre\lib\ext\dnsns.jar;D:\environment\java\jdk1.8\jre\lib\ext\jaccess.jar;D:\environment\java\jdk1.8\jre\lib\ext\jfxrt.jar;D:\environment\java\jdk1.8\jre\lib\ext\localedata.jar;D:\environment\java\jdk1.8\jre\lib\ext\nashorn.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunec.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunjce_provider.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunmscapi.jar;D:\environment\java\jdk1.8\jre\lib\ext\sunpkcs11.jar;D:\environment\java\jdk1.8\jre\lib\ext\zipfs.jar;D:\environment\java\jdk1.8\jre\lib\javaws.jar;D:\environment\java\jdk1.8\jre\lib\jce.jar;D:\environment\java\jdk1.8\jre\lib\jfr.jar;D:\environment\java\jdk1.8\jre\lib\jfxswt.jar;D:\environment\java\jdk1.8\jre\lib\jsse.jar;D:\environment\java\jdk1.8\jre\lib\management-agent.jar;D:\environment\java\jdk1.8\jre\lib\plugin.jar;D:\environment\java\jdk1.8\jre\lib\resources.jar;D:\environment\java\jdk1.8\jre\lib\rt.jar;E:\桌面\java学习\production\基础语法 com.kuang.struct.DoWhileDemon02
=============================
0
Process finished with exit code 0
标签：jdk1.8,Java,lib,jar,jre,environment,DoWhile,While,java 来源： https://blog.csdn.net/hello_sunny123/article/details/114272351